pub struct String { /* private fields */ }
Expand description
A UTF-8–encoded, growable string.
String
is the most common string type. It has ownership over the contents
of the string, stored in a heap-allocated buffer (see Representation).
It is closely related to its borrowed counterpart, the primitive str
.
§Examples
You can create a String
from a literal string with String::from
:
let hello = String::from("Hello, world!");
You can append a char
to a String
with the push
method, and
append a &str
with the push_str
method:
let mut hello = String::from("Hello, ");
hello.push('w');
hello.push_str("orld!");
If you have a vector of UTF-8 bytes, you can create a String
from it with
the from_utf8
method:
// some bytes, in a vector
let sparkle_heart = vec![240, 159, 146, 150];
// We know these bytes are valid, so we'll use `unwrap()`.
let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
assert_eq!("💖", sparkle_heart);
§UTF-8
String
s are always valid UTF-8. If you need a non-UTF-8 string, consider
OsString
. It is similar, but without the UTF-8 constraint. Because UTF-8
is a variable width encoding, String
s are typically smaller than an array of
the same chars
:
use std::mem;
// `s` is ASCII which represents each `char` as one byte
let s = "hello";
assert_eq!(s.len(), 5);
// A `char` array with the same contents would be longer because
// every `char` is four bytes
let s = ['h', 'e', 'l', 'l', 'o'];
let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
assert_eq!(size, 20);
// However, for non-ASCII strings, the difference will be smaller
// and sometimes they are the same
let s = "💖💖💖💖💖";
assert_eq!(s.len(), 20);
let s = ['💖', '💖', '💖', '💖', '💖'];
let size: usize = s.into_iter().map(|c| mem::size_of_val(&c)).sum();
assert_eq!(size, 20);
This raises interesting questions as to how s[i]
should work.
What should i
be here? Several options include byte indices and
char
indices but, because of UTF-8 encoding, only byte indices
would provide constant time indexing. Getting the i
th char
, for
example, is available using chars
:
let s = "hello";
let third_character = s.chars().nth(2);
assert_eq!(third_character, Some('l'));
let s = "💖💖💖💖💖";
let third_character = s.chars().nth(2);
assert_eq!(third_character, Some('💖'));
Next, what should s[i]
return? Because indexing returns a reference
to underlying data it could be &u8
, &[u8]
, or something else similar.
Since we’re only providing one index, &u8
makes the most sense but that
might not be what the user expects and can be explicitly achieved with
as_bytes()
:
// The first byte is 104 - the byte value of `'h'`
let s = "hello";
assert_eq!(s.as_bytes()[0], 104);
// or
assert_eq!(s.as_bytes()[0], b'h');
// The first byte is 240 which isn't obviously useful
let s = "💖💖💖💖💖";
assert_eq!(s.as_bytes()[0], 240);
Due to these ambiguities/restrictions, indexing with a usize
is simply
forbidden:
let s = "hello";
// The following will not compile!
println!("The first letter of s is {}", s[0]);
It is more clear, however, how &s[i..j]
should work (that is,
indexing with a range). It should accept byte indices (to be constant-time)
and return a &str
which is UTF-8 encoded. This is also called “string slicing”.
Note this will panic if the byte indices provided are not character
boundaries - see is_char_boundary
for more details. See the implementations
for SliceIndex<str>
for more details on string slicing. For a non-panicking
version of string slicing, see get
.
The bytes
and chars
methods return iterators over the bytes and
codepoints of the string, respectively. To iterate over codepoints along
with byte indices, use char_indices
.
§Deref
String
implements Deref<Target = str>
, and so inherits all of str
’s
methods. In addition, this means that you can pass a String
to a
function which takes a &str
by using an ampersand (&
):
fn takes_str(s: &str) { }
let s = String::from("Hello");
takes_str(&s);
This will create a &str
from the String
and pass it in. This
conversion is very inexpensive, and so generally, functions will accept
&str
s as arguments unless they need a String
for some specific
reason.
In certain cases Rust doesn’t have enough information to make this
conversion, known as Deref
coercion. In the following example a string
slice &'a str
implements the trait TraitExample
, and the function
example_func
takes anything that implements the trait. In this case Rust
would need to make two implicit conversions, which Rust doesn’t have the
means to do. For that reason, the following example will not compile.
trait TraitExample {}
impl<'a> TraitExample for &'a str {}
fn example_func<A: TraitExample>(example_arg: A) {}
let example_string = String::from("example_string");
example_func(&example_string);
There are two options that would work instead. The first would be to
change the line example_func(&example_string);
to
example_func(example_string.as_str());
, using the method as_str()
to explicitly extract the string slice containing the string. The second
way changes example_func(&example_string);
to
example_func(&*example_string);
. In this case we are dereferencing a
String
to a str
, then referencing the str
back to
&str
. The second way is more idiomatic, however both work to do the
conversion explicitly rather than relying on the implicit conversion.
§Representation
A String
is made up of three components: a pointer to some bytes, a
length, and a capacity. The pointer points to the internal buffer which String
uses to store its data. The length is the number of bytes currently stored
in the buffer, and the capacity is the size of the buffer in bytes. As such,
the length will always be less than or equal to the capacity.
This buffer is always stored on the heap.
You can look at these with the as_ptr
, len
, and capacity
methods:
use std::mem;
let story = String::from("Once upon a time...");
// Prevent automatically dropping the String's data
let mut story = mem::ManuallyDrop::new(story);
let ptr = story.as_mut_ptr();
let len = story.len();
let capacity = story.capacity();
// story has nineteen bytes
assert_eq!(19, len);
// We can re-build a String out of ptr, len, and capacity. This is all
// unsafe because we are responsible for making sure the components are
// valid:
let s = unsafe { String::from_raw_parts(ptr, len, capacity) } ;
assert_eq!(String::from("Once upon a time..."), s);
If a String
has enough capacity, adding elements to it will not
re-allocate. For example, consider this program:
let mut s = String::new();
println!("{}", s.capacity());
for _ in 0..5 {
s.push_str("hello");
println!("{}", s.capacity());
}
This will output the following:
0
8
16
16
32
32
At first, we have no memory allocated at all, but as we append to the
string, it increases its capacity appropriately. If we instead use the
with_capacity
method to allocate the correct capacity initially:
let mut s = String::with_capacity(25);
println!("{}", s.capacity());
for _ in 0..5 {
s.push_str("hello");
println!("{}", s.capacity());
}
We end up with a different output:
25
25
25
25
25
25
Here, there’s no need to allocate more memory inside the loop.
Implementations§
source§impl String
impl String
1.0.0 (const: 1.39.0) · sourcepub const fn new() -> String
pub const fn new() -> String
Creates a new empty String
.
Given that the String
is empty, this will not allocate any initial
buffer. While that means that this initial operation is very
inexpensive, it may cause excessive allocation later when you add
data. If you have an idea of how much data the String
will hold,
consider the with_capacity
method to prevent excessive
re-allocation.
§Examples
let s = String::new();
1.0.0 · sourcepub fn with_capacity(capacity: usize) -> String
pub fn with_capacity(capacity: usize) -> String
Creates a new empty String
with at least the specified capacity.
String
s have an internal buffer to hold their data. The capacity is
the length of that buffer, and can be queried with the capacity
method. This method creates an empty String
, but one with an initial
buffer that can hold at least capacity
bytes. This is useful when you
may be appending a bunch of data to the String
, reducing the number of
reallocations it needs to do.
If the given capacity is 0
, no allocation will occur, and this method
is identical to the new
method.
§Examples
let mut s = String::with_capacity(10);
// The String contains no chars, even though it has capacity for more
assert_eq!(s.len(), 0);
// These are all done without reallocating...
let cap = s.capacity();
for _ in 0..10 {
s.push('a');
}
assert_eq!(s.capacity(), cap);
// ...but this may make the string reallocate
s.push('a');
sourcepub fn try_with_capacity(capacity: usize) -> Result<String, TryReserveError>
🔬This is a nightly-only experimental API. (try_with_capacity
)
pub fn try_with_capacity(capacity: usize) -> Result<String, TryReserveError>
try_with_capacity
)1.0.0 · sourcepub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error>
pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error>
Converts a vector of bytes to a String
.
A string (String
) is made of bytes (u8
), and a vector of bytes
(Vec<u8>
) is made of bytes, so this function converts between the
two. Not all byte slices are valid String
s, however: String
requires that it is valid UTF-8. from_utf8()
checks to ensure that
the bytes are valid UTF-8, and then does the conversion.
If you are sure that the byte slice is valid UTF-8, and you don’t want
to incur the overhead of the validity check, there is an unsafe version
of this function, from_utf8_unchecked
, which has the same behavior
but skips the check.
This method will take care to not copy the vector, for efficiency’s sake.
If you need a &str
instead of a String
, consider
str::from_utf8
.
The inverse of this method is into_bytes
.
§Errors
Returns Err
if the slice is not UTF-8 with a description as to why the
provided bytes are not UTF-8. The vector you moved in is also included.
§Examples
Basic usage:
// some bytes, in a vector
let sparkle_heart = vec![240, 159, 146, 150];
// We know these bytes are valid, so we'll use `unwrap()`.
let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
assert_eq!("💖", sparkle_heart);
Incorrect bytes:
// some invalid bytes, in a vector
let sparkle_heart = vec![0, 159, 146, 150];
assert!(String::from_utf8(sparkle_heart).is_err());
See the docs for FromUtf8Error
for more details on what you can do
with this error.
1.0.0 · sourcepub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str>
pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str>
Converts a slice of bytes to a string, including invalid characters.
Strings are made of bytes (u8
), and a slice of bytes
(&[u8]
) is made of bytes, so this function converts
between the two. Not all byte slices are valid strings, however: strings
are required to be valid UTF-8. During this conversion,
from_utf8_lossy()
will replace any invalid UTF-8 sequences with
U+FFFD REPLACEMENT CHARACTER
, which looks like this: �
If you are sure that the byte slice is valid UTF-8, and you don’t want
to incur the overhead of the conversion, there is an unsafe version
of this function, from_utf8_unchecked
, which has the same behavior
but skips the checks.
This function returns a Cow<'a, str>
. If our byte slice is invalid
UTF-8, then we need to insert the replacement characters, which will
change the size of the string, and hence, require a String
. But if
it’s already valid UTF-8, we don’t need a new allocation. This return
type allows us to handle both cases.
§Examples
Basic usage:
// some bytes, in a vector
let sparkle_heart = vec![240, 159, 146, 150];
let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
assert_eq!("💖", sparkle_heart);
Incorrect bytes:
// some invalid bytes
let input = b"Hello \xF0\x90\x80World";
let output = String::from_utf8_lossy(input);
assert_eq!("Hello �World", output);
1.0.0 · sourcepub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error>
pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error>
Decode a UTF-16–encoded vector v
into a String
, returning Err
if v
contains any invalid data.
§Examples
// 𝄞music
let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
0x0073, 0x0069, 0x0063];
assert_eq!(String::from("𝄞music"),
String::from_utf16(v).unwrap());
// 𝄞mu<invalid>ic
let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
0xD800, 0x0069, 0x0063];
assert!(String::from_utf16(v).is_err());
1.0.0 · sourcepub fn from_utf16_lossy(v: &[u16]) -> String
pub fn from_utf16_lossy(v: &[u16]) -> String
Decode a UTF-16–encoded slice v
into a String
, replacing
invalid data with the replacement character (U+FFFD
).
Unlike from_utf8_lossy
which returns a Cow<'a, str>
,
from_utf16_lossy
returns a String
since the UTF-16 to UTF-8
conversion requires a memory allocation.
§Examples
// 𝄞mus<invalid>ic<invalid>
let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
0x0073, 0xDD1E, 0x0069, 0x0063,
0xD834];
assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
String::from_utf16_lossy(v));
sourcepub fn from_utf16le(v: &[u8]) -> Result<String, FromUtf16Error>
🔬This is a nightly-only experimental API. (str_from_utf16_endian
)
pub fn from_utf16le(v: &[u8]) -> Result<String, FromUtf16Error>
str_from_utf16_endian
)Decode a UTF-16LE–encoded vector v
into a String
, returning Err
if v
contains any invalid data.
§Examples
Basic usage:
#![feature(str_from_utf16_endian)]
// 𝄞music
let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
0x73, 0x00, 0x69, 0x00, 0x63, 0x00];
assert_eq!(String::from("𝄞music"),
String::from_utf16le(v).unwrap());
// 𝄞mu<invalid>ic
let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
0x00, 0xD8, 0x69, 0x00, 0x63, 0x00];
assert!(String::from_utf16le(v).is_err());
sourcepub fn from_utf16le_lossy(v: &[u8]) -> String
🔬This is a nightly-only experimental API. (str_from_utf16_endian
)
pub fn from_utf16le_lossy(v: &[u8]) -> String
str_from_utf16_endian
)Decode a UTF-16LE–encoded slice v
into a String
, replacing
invalid data with the replacement character (U+FFFD
).
Unlike from_utf8_lossy
which returns a Cow<'a, str>
,
from_utf16le_lossy
returns a String
since the UTF-16 to UTF-8
conversion requires a memory allocation.
§Examples
Basic usage:
#![feature(str_from_utf16_endian)]
// 𝄞mus<invalid>ic<invalid>
let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
0x73, 0x00, 0x1E, 0xDD, 0x69, 0x00, 0x63, 0x00,
0x34, 0xD8];
assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
String::from_utf16le_lossy(v));
sourcepub fn from_utf16be(v: &[u8]) -> Result<String, FromUtf16Error>
🔬This is a nightly-only experimental API. (str_from_utf16_endian
)
pub fn from_utf16be(v: &[u8]) -> Result<String, FromUtf16Error>
str_from_utf16_endian
)Decode a UTF-16BE–encoded vector v
into a String
, returning Err
if v
contains any invalid data.
§Examples
Basic usage:
#![feature(str_from_utf16_endian)]
// 𝄞music
let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
0x00, 0x73, 0x00, 0x69, 0x00, 0x63];
assert_eq!(String::from("𝄞music"),
String::from_utf16be(v).unwrap());
// 𝄞mu<invalid>ic
let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
0xD8, 0x00, 0x00, 0x69, 0x00, 0x63];
assert!(String::from_utf16be(v).is_err());
sourcepub fn from_utf16be_lossy(v: &[u8]) -> String
🔬This is a nightly-only experimental API. (str_from_utf16_endian
)
pub fn from_utf16be_lossy(v: &[u8]) -> String
str_from_utf16_endian
)Decode a UTF-16BE–encoded slice v
into a String
, replacing
invalid data with the replacement character (U+FFFD
).
Unlike from_utf8_lossy
which returns a Cow<'a, str>
,
from_utf16le_lossy
returns a String
since the UTF-16 to UTF-8
conversion requires a memory allocation.
§Examples
Basic usage:
#![feature(str_from_utf16_endian)]
// 𝄞mus<invalid>ic<invalid>
let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
0x00, 0x73, 0xDD, 0x1E, 0x00, 0x69, 0x00, 0x63,
0xD8, 0x34];
assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
String::from_utf16be_lossy(v));
sourcepub fn into_raw_parts(self) -> (*mut u8, usize, usize)
🔬This is a nightly-only experimental API. (vec_into_raw_parts
)
pub fn into_raw_parts(self) -> (*mut u8, usize, usize)
vec_into_raw_parts
)Decomposes a String
into its raw components: (pointer, length, capacity)
.
Returns the raw pointer to the underlying data, the length of
the string (in bytes), and the allocated capacity of the data
(in bytes). These are the same arguments in the same order as
the arguments to from_raw_parts
.
After calling this function, the caller is responsible for the
memory previously managed by the String
. The only way to do
this is to convert the raw pointer, length, and capacity back
into a String
with the from_raw_parts
function, allowing
the destructor to perform the cleanup.
§Examples
#![feature(vec_into_raw_parts)]
let s = String::from("hello");
let (ptr, len, cap) = s.into_raw_parts();
let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
assert_eq!(rebuilt, "hello");
1.0.0 · sourcepub unsafe fn from_raw_parts(
buf: *mut u8,
length: usize,
capacity: usize,
) -> String
pub unsafe fn from_raw_parts( buf: *mut u8, length: usize, capacity: usize, ) -> String
Creates a new String
from a pointer, a length and a capacity.
§Safety
This is highly unsafe, due to the number of invariants that aren’t checked:
- The memory at
buf
needs to have been previously allocated by the same allocator the standard library uses, with a required alignment of exactly 1. length
needs to be less than or equal tocapacity
.capacity
needs to be the correct value.- The first
length
bytes atbuf
need to be valid UTF-8.
Violating these may cause problems like corrupting the allocator’s
internal data structures. For example, it is normally not safe to
build a String
from a pointer to a C char
array containing UTF-8
unless you are certain that array was originally allocated by the
Rust standard library’s allocator.
The ownership of buf
is effectively transferred to the
String
which may then deallocate, reallocate or change the
contents of memory pointed to by the pointer at will. Ensure
that nothing else uses the pointer after calling this
function.
§Examples
use std::mem;
unsafe {
let s = String::from("hello");
// Prevent automatically dropping the String's data
let mut s = mem::ManuallyDrop::new(s);
let ptr = s.as_mut_ptr();
let len = s.len();
let capacity = s.capacity();
let s = String::from_raw_parts(ptr, len, capacity);
assert_eq!(String::from("hello"), s);
}
1.0.0 · sourcepub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String
pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String
Converts a vector of bytes to a String
without checking that the
string contains valid UTF-8.
See the safe version, from_utf8
, for more details.
§Safety
This function is unsafe because it does not check that the bytes passed
to it are valid UTF-8. If this constraint is violated, it may cause
memory unsafety issues with future users of the String
, as the rest of
the standard library assumes that String
s are valid UTF-8.
§Examples
// some bytes, in a vector
let sparkle_heart = vec![240, 159, 146, 150];
let sparkle_heart = unsafe {
String::from_utf8_unchecked(sparkle_heart)
};
assert_eq!("💖", sparkle_heart);
1.0.0 · sourcepub fn into_bytes(self) -> Vec<u8> ⓘ
pub fn into_bytes(self) -> Vec<u8> ⓘ
Converts a String
into a byte vector.
This consumes the String
, so we do not need to copy its contents.
§Examples
let s = String::from("hello");
let bytes = s.into_bytes();
assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
1.7.0 · sourcepub fn as_str(&self) -> &str
pub fn as_str(&self) -> &str
Extracts a string slice containing the entire String
.
§Examples
let s = String::from("foo");
assert_eq!("foo", s.as_str());
1.7.0 · sourcepub fn as_mut_str(&mut self) -> &mut str
pub fn as_mut_str(&mut self) -> &mut str
Converts a String
into a mutable string slice.
§Examples
let mut s = String::from("foobar");
let s_mut_str = s.as_mut_str();
s_mut_str.make_ascii_uppercase();
assert_eq!("FOOBAR", s_mut_str);
1.0.0 · sourcepub fn push_str(&mut self, string: &str)
pub fn push_str(&mut self, string: &str)
Appends a given string slice onto the end of this String
.
§Examples
let mut s = String::from("foo");
s.push_str("bar");
assert_eq!("foobar", s);
sourcepub fn extend_from_within<R>(&mut self, src: R)where
R: RangeBounds<usize>,
🔬This is a nightly-only experimental API. (string_extend_from_within
)
pub fn extend_from_within<R>(&mut self, src: R)where
R: RangeBounds<usize>,
string_extend_from_within
)Copies elements from src
range to the end of the string.
§Panics
Panics if the starting point or end point do not lie on a char
boundary, or if they’re out of bounds.
§Examples
#![feature(string_extend_from_within)]
let mut string = String::from("abcde");
string.extend_from_within(2..);
assert_eq!(string, "abcdecde");
string.extend_from_within(..2);
assert_eq!(string, "abcdecdeab");
string.extend_from_within(4..8);
assert_eq!(string, "abcdecdeabecde");
1.0.0 · sourcepub fn capacity(&self) -> usize
pub fn capacity(&self) -> usize
Returns this String
’s capacity, in bytes.
§Examples
let s = String::with_capacity(10);
assert!(s.capacity() >= 10);
1.0.0 · sourcepub fn reserve(&mut self, additional: usize)
pub fn reserve(&mut self, additional: usize)
Reserves capacity for at least additional
bytes more than the
current length. The allocator may reserve more space to speculatively
avoid frequent allocations. After calling reserve
,
capacity will be greater than or equal to self.len() + additional
.
Does nothing if capacity is already sufficient.
§Panics
Panics if the new capacity overflows usize
.
§Examples
Basic usage:
let mut s = String::new();
s.reserve(10);
assert!(s.capacity() >= 10);
This might not actually increase the capacity:
let mut s = String::with_capacity(10);
s.push('a');
s.push('b');
// s now has a length of 2 and a capacity of at least 10
let capacity = s.capacity();
assert_eq!(2, s.len());
assert!(capacity >= 10);
// Since we already have at least an extra 8 capacity, calling this...
s.reserve(8);
// ... doesn't actually increase.
assert_eq!(capacity, s.capacity());
1.0.0 · sourcepub fn reserve_exact(&mut self, additional: usize)
pub fn reserve_exact(&mut self, additional: usize)
Reserves the minimum capacity for at least additional
bytes more than
the current length. Unlike reserve
, this will not
deliberately over-allocate to speculatively avoid frequent allocations.
After calling reserve_exact
, capacity will be greater than or equal to
self.len() + additional
. Does nothing if the capacity is already
sufficient.
§Panics
Panics if the new capacity overflows usize
.
§Examples
Basic usage:
let mut s = String::new();
s.reserve_exact(10);
assert!(s.capacity() >= 10);
This might not actually increase the capacity:
let mut s = String::with_capacity(10);
s.push('a');
s.push('b');
// s now has a length of 2 and a capacity of at least 10
let capacity = s.capacity();
assert_eq!(2, s.len());
assert!(capacity >= 10);
// Since we already have at least an extra 8 capacity, calling this...
s.reserve_exact(8);
// ... doesn't actually increase.
assert_eq!(capacity, s.capacity());
1.57.0 · sourcepub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>
pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>
Tries to reserve capacity for at least additional
bytes more than the
current length. The allocator may reserve more space to speculatively
avoid frequent allocations. After calling try_reserve
, capacity will be
greater than or equal to self.len() + additional
if it returns
Ok(())
. Does nothing if capacity is already sufficient. This method
preserves the contents even if an error occurs.
§Errors
If the capacity overflows, or the allocator reports a failure, then an error is returned.
§Examples
use std::collections::TryReserveError;
fn process_data(data: &str) -> Result<String, TryReserveError> {
let mut output = String::new();
// Pre-reserve the memory, exiting if we can't
output.try_reserve(data.len())?;
// Now we know this can't OOM in the middle of our complex work
output.push_str(data);
Ok(output)
}
1.57.0 · sourcepub fn try_reserve_exact(
&mut self,
additional: usize,
) -> Result<(), TryReserveError>
pub fn try_reserve_exact( &mut self, additional: usize, ) -> Result<(), TryReserveError>
Tries to reserve the minimum capacity for at least additional
bytes
more than the current length. Unlike try_reserve
, this will not
deliberately over-allocate to speculatively avoid frequent allocations.
After calling try_reserve_exact
, capacity will be greater than or
equal to self.len() + additional
if it returns Ok(())
.
Does nothing if the capacity is already sufficient.
Note that the allocator may give the collection more space than it
requests. Therefore, capacity can not be relied upon to be precisely
minimal. Prefer try_reserve
if future insertions are expected.
§Errors
If the capacity overflows, or the allocator reports a failure, then an error is returned.
§Examples
use std::collections::TryReserveError;
fn process_data(data: &str) -> Result<String, TryReserveError> {
let mut output = String::new();
// Pre-reserve the memory, exiting if we can't
output.try_reserve_exact(data.len())?;
// Now we know this can't OOM in the middle of our complex work
output.push_str(data);
Ok(output)
}
1.0.0 · sourcepub fn shrink_to_fit(&mut self)
pub fn shrink_to_fit(&mut self)
Shrinks the capacity of this String
to match its length.
§Examples
let mut s = String::from("foo");
s.reserve(100);
assert!(s.capacity() >= 100);
s.shrink_to_fit();
assert_eq!(3, s.capacity());
1.56.0 · sourcepub fn shrink_to(&mut self, min_capacity: usize)
pub fn shrink_to(&mut self, min_capacity: usize)
Shrinks the capacity of this String
with a lower bound.
The capacity will remain at least as large as both the length and the supplied value.
If the current capacity is less than the lower limit, this is a no-op.
§Examples
let mut s = String::from("foo");
s.reserve(100);
assert!(s.capacity() >= 100);
s.shrink_to(10);
assert!(s.capacity() >= 10);
s.shrink_to(0);
assert!(s.capacity() >= 3);
1.0.0 · sourcepub fn truncate(&mut self, new_len: usize)
pub fn truncate(&mut self, new_len: usize)
Shortens this String
to the specified length.
If new_len
is greater than or equal to the string’s current length, this has no
effect.
Note that this method has no effect on the allocated capacity of the string
§Panics
Panics if new_len
does not lie on a char
boundary.
§Examples
let mut s = String::from("hello");
s.truncate(2);
assert_eq!("he", s);
1.0.0 · sourcepub fn remove(&mut self, idx: usize) -> char
pub fn remove(&mut self, idx: usize) -> char
Removes a char
from this String
at a byte position and returns it.
This is an O(n) operation, as it requires copying every element in the buffer.
§Panics
Panics if idx
is larger than or equal to the String
’s length,
or if it does not lie on a char
boundary.
§Examples
let mut s = String::from("abç");
assert_eq!(s.remove(0), 'a');
assert_eq!(s.remove(1), 'ç');
assert_eq!(s.remove(0), 'b');
sourcepub fn remove_matches<P>(&mut self, pat: P)where
P: Pattern,
🔬This is a nightly-only experimental API. (string_remove_matches
)
pub fn remove_matches<P>(&mut self, pat: P)where
P: Pattern,
string_remove_matches
)Remove all matches of pattern pat
in the String
.
§Examples
#![feature(string_remove_matches)]
let mut s = String::from("Trees are not green, the sky is not blue.");
s.remove_matches("not ");
assert_eq!("Trees are green, the sky is blue.", s);
Matches will be detected and removed iteratively, so in cases where patterns overlap, only the first pattern will be removed:
#![feature(string_remove_matches)]
let mut s = String::from("banana");
s.remove_matches("ana");
assert_eq!("bna", s);
1.26.0 · sourcepub fn retain<F>(&mut self, f: F)
pub fn retain<F>(&mut self, f: F)
Retains only the characters specified by the predicate.
In other words, remove all characters c
such that f(c)
returns false
.
This method operates in place, visiting each character exactly once in the
original order, and preserves the order of the retained characters.
§Examples
let mut s = String::from("f_o_ob_ar");
s.retain(|c| c != '_');
assert_eq!(s, "foobar");
Because the elements are visited exactly once in the original order, external state may be used to decide which elements to keep.
let mut s = String::from("abcde");
let keep = [false, true, true, false, true];
let mut iter = keep.iter();
s.retain(|_| *iter.next().unwrap());
assert_eq!(s, "bce");
1.0.0 · sourcepub fn insert(&mut self, idx: usize, ch: char)
pub fn insert(&mut self, idx: usize, ch: char)
Inserts a character into this String
at a byte position.
This is an O(n) operation as it requires copying every element in the buffer.
§Panics
Panics if idx
is larger than the String
’s length, or if it does not
lie on a char
boundary.
§Examples
let mut s = String::with_capacity(3);
s.insert(0, 'f');
s.insert(1, 'o');
s.insert(2, 'o');
assert_eq!("foo", s);
1.16.0 · sourcepub fn insert_str(&mut self, idx: usize, string: &str)
pub fn insert_str(&mut self, idx: usize, string: &str)
Inserts a string slice into this String
at a byte position.
This is an O(n) operation as it requires copying every element in the buffer.
§Panics
Panics if idx
is larger than the String
’s length, or if it does not
lie on a char
boundary.
§Examples
let mut s = String::from("bar");
s.insert_str(0, "foo");
assert_eq!("foobar", s);
1.0.0 · sourcepub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> ⓘ
pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> ⓘ
Returns a mutable reference to the contents of this String
.
§Safety
This function is unsafe because the returned &mut Vec
allows writing
bytes which are not valid UTF-8. If this constraint is violated, using
the original String
after dropping the &mut Vec
may violate memory
safety, as the rest of the standard library assumes that String
s are
valid UTF-8.
§Examples
let mut s = String::from("hello");
unsafe {
let vec = s.as_mut_vec();
assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
vec.reverse();
}
assert_eq!(s, "olleh");
1.0.0 · sourcepub fn len(&self) -> usize
pub fn len(&self) -> usize
Returns the length of this String
, in bytes, not char
s or
graphemes. In other words, it might not be what a human considers the
length of the string.
§Examples
let a = String::from("foo");
assert_eq!(a.len(), 3);
let fancy_f = String::from("ƒoo");
assert_eq!(fancy_f.len(), 4);
assert_eq!(fancy_f.chars().count(), 3);
1.0.0 · sourcepub fn is_empty(&self) -> bool
pub fn is_empty(&self) -> bool
Returns true
if this String
has a length of zero, and false
otherwise.
§Examples
let mut v = String::new();
assert!(v.is_empty());
v.push('a');
assert!(!v.is_empty());
1.16.0 · sourcepub fn split_off(&mut self, at: usize) -> String
pub fn split_off(&mut self, at: usize) -> String
Splits the string into two at the given byte index.
Returns a newly allocated String
. self
contains bytes [0, at)
, and
the returned String
contains bytes [at, len)
. at
must be on the
boundary of a UTF-8 code point.
Note that the capacity of self
does not change.
§Panics
Panics if at
is not on a UTF-8
code point boundary, or if it is beyond the last
code point of the string.
§Examples
let mut hello = String::from("Hello, World!");
let world = hello.split_off(7);
assert_eq!(hello, "Hello, ");
assert_eq!(world, "World!");
1.0.0 · sourcepub fn clear(&mut self)
pub fn clear(&mut self)
Truncates this String
, removing all contents.
While this means the String
will have a length of zero, it does not
touch its capacity.
§Examples
let mut s = String::from("foo");
s.clear();
assert!(s.is_empty());
assert_eq!(0, s.len());
assert_eq!(3, s.capacity());
1.6.0 · sourcepub fn drain<R>(&mut self, range: R) -> Drain<'_> ⓘwhere
R: RangeBounds<usize>,
pub fn drain<R>(&mut self, range: R) -> Drain<'_> ⓘwhere
R: RangeBounds<usize>,
Removes the specified range from the string in bulk, returning all removed characters as an iterator.
The returned iterator keeps a mutable borrow on the string to optimize its implementation.
§Panics
Panics if the starting point or end point do not lie on a char
boundary, or if they’re out of bounds.
§Leaking
If the returned iterator goes out of scope without being dropped (due to
core::mem::forget
, for example), the string may still contain a copy
of any drained characters, or may have lost characters arbitrarily,
including characters outside the range.
§Examples
let mut s = String::from("α is alpha, β is beta");
let beta_offset = s.find('β').unwrap_or(s.len());
// Remove the range up until the β from the string
let t: String = s.drain(..beta_offset).collect();
assert_eq!(t, "α is alpha, ");
assert_eq!(s, "β is beta");
// A full range clears the string, like `clear()` does
s.drain(..);
assert_eq!(s, "");
1.27.0 · sourcepub fn replace_range<R>(&mut self, range: R, replace_with: &str)where
R: RangeBounds<usize>,
pub fn replace_range<R>(&mut self, range: R, replace_with: &str)where
R: RangeBounds<usize>,
Removes the specified range in the string, and replaces it with the given string. The given string doesn’t need to be the same length as the range.
§Panics
Panics if the starting point or end point do not lie on a char
boundary, or if they’re out of bounds.
§Examples
let mut s = String::from("α is alpha, β is beta");
let beta_offset = s.find('β').unwrap_or(s.len());
// Replace the range up until the β from the string
s.replace_range(..beta_offset, "Α is capital alpha; ");
assert_eq!(s, "Α is capital alpha; β is beta");
1.4.0 · sourcepub fn into_boxed_str(self) -> Box<str>
pub fn into_boxed_str(self) -> Box<str>
Converts this String
into a Box<str>
.
Before doing the conversion, this method discards excess capacity like shrink_to_fit
.
Note that this call may reallocate and copy the bytes of the string.
§Examples
let s = String::from("hello");
let b = s.into_boxed_str();
1.72.0 · sourcepub fn leak<'a>(self) -> &'a mut str
pub fn leak<'a>(self) -> &'a mut str
Consumes and leaks the String
, returning a mutable reference to the contents,
&'a mut str
.
The caller has free choice over the returned lifetime, including 'static
. Indeed,
this function is ideally used for data that lives for the remainder of the program’s life,
as dropping the returned reference will cause a memory leak.
It does not reallocate or shrink the String
, so the leaked allocation may include unused
capacity that is not part of the returned slice. If you want to discard excess capacity,
call into_boxed_str
, and then Box::leak
instead. However, keep in mind that
trimming the capacity may result in a reallocation and copy.
§Examples
let x = String::from("bucket");
let static_ref: &'static mut str = x.leak();
assert_eq!(static_ref, "bucket");
Methods from Deref<Target = str>§
1.0.0 · sourcepub fn is_empty(&self) -> bool
pub fn is_empty(&self) -> bool
Returns true
if self
has a length of zero bytes.
§Examples
let s = "";
assert!(s.is_empty());
let s = "not empty";
assert!(!s.is_empty());
1.9.0 · sourcepub fn is_char_boundary(&self, index: usize) -> bool
pub fn is_char_boundary(&self, index: usize) -> bool
Checks that index
-th byte is the first byte in a UTF-8 code point
sequence or the end of the string.
The start and end of the string (when index == self.len()
) are
considered to be boundaries.
Returns false
if index
is greater than self.len()
.
§Examples
let s = "Löwe 老虎 Léopard";
assert!(s.is_char_boundary(0));
// start of `老`
assert!(s.is_char_boundary(6));
assert!(s.is_char_boundary(s.len()));
// second byte of `ö`
assert!(!s.is_char_boundary(2));
// third byte of `老`
assert!(!s.is_char_boundary(8));
sourcepub fn floor_char_boundary(&self, index: usize) -> usize
🔬This is a nightly-only experimental API. (round_char_boundary
)
pub fn floor_char_boundary(&self, index: usize) -> usize
round_char_boundary
)Finds the closest x
not exceeding index
where is_char_boundary(x)
is true
.
This method can help you truncate a string so that it’s still valid UTF-8, but doesn’t exceed a given number of bytes. Note that this is done purely at the character level and can still visually split graphemes, even though the underlying characters aren’t split. For example, the emoji 🧑🔬 (scientist) could be split so that the string only includes 🧑 (person) instead.
§Examples
#![feature(round_char_boundary)]
let s = "❤️🧡💛💚💙💜";
assert_eq!(s.len(), 26);
assert!(!s.is_char_boundary(13));
let closest = s.floor_char_boundary(13);
assert_eq!(closest, 10);
assert_eq!(&s[..closest], "❤️🧡");
sourcepub fn ceil_char_boundary(&self, index: usize) -> usize
🔬This is a nightly-only experimental API. (round_char_boundary
)
pub fn ceil_char_boundary(&self, index: usize) -> usize
round_char_boundary
)Finds the closest x
not below index
where is_char_boundary(x)
is true
.
If index
is greater than the length of the string, this returns the length of the string.
This method is the natural complement to floor_char_boundary
. See that method
for more details.
§Examples
#![feature(round_char_boundary)]
let s = "❤️🧡💛💚💙💜";
assert_eq!(s.len(), 26);
assert!(!s.is_char_boundary(13));
let closest = s.ceil_char_boundary(13);
assert_eq!(closest, 14);
assert_eq!(&s[..closest], "❤️🧡💛");
1.20.0 · sourcepub unsafe fn as_bytes_mut(&mut self) -> &mut [u8] ⓘ
pub unsafe fn as_bytes_mut(&mut self) -> &mut [u8] ⓘ
Converts a mutable string slice to a mutable byte slice.
§Safety
The caller must ensure that the content of the slice is valid UTF-8
before the borrow ends and the underlying str
is used.
Use of a str
whose contents are not valid UTF-8 is undefined behavior.
§Examples
Basic usage:
let mut s = String::from("Hello");
let bytes = unsafe { s.as_bytes_mut() };
assert_eq!(b"Hello", bytes);
Mutability:
let mut s = String::from("🗻∈🌏");
unsafe {
let bytes = s.as_bytes_mut();
bytes[0] = 0xF0;
bytes[1] = 0x9F;
bytes[2] = 0x8D;
bytes[3] = 0x94;
}
assert_eq!("🍔∈🌏", s);
1.0.0 · sourcepub fn as_ptr(&self) -> *const u8
pub fn as_ptr(&self) -> *const u8
Converts a string slice to a raw pointer.
As string slices are a slice of bytes, the raw pointer points to a
u8
. This pointer will be pointing to the first byte of the string
slice.
The caller must ensure that the returned pointer is never written to.
If you need to mutate the contents of the string slice, use as_mut_ptr
.
§Examples
let s = "Hello";
let ptr = s.as_ptr();
1.36.0 · sourcepub fn as_mut_ptr(&mut self) -> *mut u8
pub fn as_mut_ptr(&mut self) -> *mut u8
Converts a mutable string slice to a raw pointer.
As string slices are a slice of bytes, the raw pointer points to a
u8
. This pointer will be pointing to the first byte of the string
slice.
It is your responsibility to make sure that the string slice only gets modified in a way that it remains valid UTF-8.
1.20.0 · sourcepub fn get<I>(&self, i: I) -> Option<&<I as SliceIndex<str>>::Output>where
I: SliceIndex<str>,
pub fn get<I>(&self, i: I) -> Option<&<I as SliceIndex<str>>::Output>where
I: SliceIndex<str>,
Returns a subslice of str
.
This is the non-panicking alternative to indexing the str
. Returns
None
whenever equivalent indexing operation would panic.
§Examples
let v = String::from("🗻∈🌏");
assert_eq!(Some("🗻"), v.get(0..4));
// indices not on UTF-8 sequence boundaries
assert!(v.get(1..).is_none());
assert!(v.get(..8).is_none());
// out of bounds
assert!(v.get(..42).is_none());
1.20.0 · sourcepub fn get_mut<I>(
&mut self,
i: I,
) -> Option<&mut <I as SliceIndex<str>>::Output>where
I: SliceIndex<str>,
pub fn get_mut<I>(
&mut self,
i: I,
) -> Option<&mut <I as SliceIndex<str>>::Output>where
I: SliceIndex<str>,
Returns a mutable subslice of str
.
This is the non-panicking alternative to indexing the str
. Returns
None
whenever equivalent indexing operation would panic.
§Examples
let mut v = String::from("hello");
// correct length
assert!(v.get_mut(0..5).is_some());
// out of bounds
assert!(v.get_mut(..42).is_none());
assert_eq!(Some("he"), v.get_mut(0..2).map(|v| &*v));
assert_eq!("hello", v);
{
let s = v.get_mut(0..2);
let s = s.map(|s| {
s.make_ascii_uppercase();
&*s
});
assert_eq!(Some("HE"), s);
}
assert_eq!("HEllo", v);
1.20.0 · sourcepub unsafe fn get_unchecked<I>(&self, i: I) -> &<I as SliceIndex<str>>::Outputwhere
I: SliceIndex<str>,
pub unsafe fn get_unchecked<I>(&self, i: I) -> &<I as SliceIndex<str>>::Outputwhere
I: SliceIndex<str>,
Returns an unchecked subslice of str
.
This is the unchecked alternative to indexing the str
.
§Safety
Callers of this function are responsible that these preconditions are satisfied:
- The starting index must not exceed the ending index;
- Indexes must be within bounds of the original slice;
- Indexes must lie on UTF-8 sequence boundaries.
Failing that, the returned string slice may reference invalid memory or
violate the invariants communicated by the str
type.
§Examples
let v = "🗻∈🌏";
unsafe {
assert_eq!("🗻", v.get_unchecked(0..4));
assert_eq!("∈", v.get_unchecked(4..7));
assert_eq!("🌏", v.get_unchecked(7..11));
}
1.20.0 · sourcepub unsafe fn get_unchecked_mut<I>(
&mut self,
i: I,
) -> &mut <I as SliceIndex<str>>::Outputwhere
I: SliceIndex<str>,
pub unsafe fn get_unchecked_mut<I>(
&mut self,
i: I,
) -> &mut <I as SliceIndex<str>>::Outputwhere
I: SliceIndex<str>,
Returns a mutable, unchecked subslice of str
.
This is the unchecked alternative to indexing the str
.
§Safety
Callers of this function are responsible that these preconditions are satisfied:
- The starting index must not exceed the ending index;
- Indexes must be within bounds of the original slice;
- Indexes must lie on UTF-8 sequence boundaries.
Failing that, the returned string slice may reference invalid memory or
violate the invariants communicated by the str
type.
§Examples
let mut v = String::from("🗻∈🌏");
unsafe {
assert_eq!("🗻", v.get_unchecked_mut(0..4));
assert_eq!("∈", v.get_unchecked_mut(4..7));
assert_eq!("🌏", v.get_unchecked_mut(7..11));
}
1.0.0 · sourcepub unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str
👎Deprecated since 1.29.0: use get_unchecked(begin..end)
instead
pub unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str
get_unchecked(begin..end)
insteadCreates a string slice from another string slice, bypassing safety checks.
This is generally not recommended, use with caution! For a safe
alternative see str
and Index
.
This new slice goes from begin
to end
, including begin
but
excluding end
.
To get a mutable string slice instead, see the
slice_mut_unchecked
method.
§Safety
Callers of this function are responsible that three preconditions are satisfied:
begin
must not exceedend
.begin
andend
must be byte positions within the string slice.begin
andend
must lie on UTF-8 sequence boundaries.
§Examples
let s = "Löwe 老虎 Léopard";
unsafe {
assert_eq!("Löwe 老虎 Léopard", s.slice_unchecked(0, 21));
}
let s = "Hello, world!";
unsafe {
assert_eq!("world", s.slice_unchecked(7, 12));
}
1.5.0 · sourcepub unsafe fn slice_mut_unchecked(
&mut self,
begin: usize,
end: usize,
) -> &mut str
👎Deprecated since 1.29.0: use get_unchecked_mut(begin..end)
instead
pub unsafe fn slice_mut_unchecked( &mut self, begin: usize, end: usize, ) -> &mut str
get_unchecked_mut(begin..end)
insteadCreates a string slice from another string slice, bypassing safety checks.
This is generally not recommended, use with caution! For a safe
alternative see str
and IndexMut
.
This new slice goes from begin
to end
, including begin
but
excluding end
.
To get an immutable string slice instead, see the
slice_unchecked
method.
§Safety
Callers of this function are responsible that three preconditions are satisfied:
begin
must not exceedend
.begin
andend
must be byte positions within the string slice.begin
andend
must lie on UTF-8 sequence boundaries.
1.4.0 · sourcepub fn split_at(&self, mid: usize) -> (&str, &str)
pub fn split_at(&self, mid: usize) -> (&str, &str)
Divides one string slice into two at an index.
The argument, mid
, should be a byte offset from the start of the
string. It must also be on the boundary of a UTF-8 code point.
The two slices returned go from the start of the string slice to mid
,
and from mid
to the end of the string slice.
To get mutable string slices instead, see the split_at_mut
method.
§Panics
Panics if mid
is not on a UTF-8 code point boundary, or if it is past
the end of the last code point of the string slice. For a non-panicking
alternative see split_at_checked
.
§Examples
let s = "Per Martin-Löf";
let (first, last) = s.split_at(3);
assert_eq!("Per", first);
assert_eq!(" Martin-Löf", last);
1.4.0 · sourcepub fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str)
pub fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str)
Divides one mutable string slice into two at an index.
The argument, mid
, should be a byte offset from the start of the
string. It must also be on the boundary of a UTF-8 code point.
The two slices returned go from the start of the string slice to mid
,
and from mid
to the end of the string slice.
To get immutable string slices instead, see the split_at
method.
§Panics
Panics if mid
is not on a UTF-8 code point boundary, or if it is past
the end of the last code point of the string slice. For a non-panicking
alternative see split_at_mut_checked
.
§Examples
let mut s = "Per Martin-Löf".to_string();
{
let (first, last) = s.split_at_mut(3);
first.make_ascii_uppercase();
assert_eq!("PER", first);
assert_eq!(" Martin-Löf", last);
}
assert_eq!("PER Martin-Löf", s);
1.80.0 · sourcepub fn split_at_checked(&self, mid: usize) -> Option<(&str, &str)>
pub fn split_at_checked(&self, mid: usize) -> Option<(&str, &str)>
Divides one string slice into two at an index.
The argument, mid
, should be a valid byte offset from the start of the
string. It must also be on the boundary of a UTF-8 code point. The
method returns None
if that’s not the case.
The two slices returned go from the start of the string slice to mid
,
and from mid
to the end of the string slice.
To get mutable string slices instead, see the split_at_mut_checked
method.
§Examples
let s = "Per Martin-Löf";
let (first, last) = s.split_at_checked(3).unwrap();
assert_eq!("Per", first);
assert_eq!(" Martin-Löf", last);
assert_eq!(None, s.split_at_checked(13)); // Inside “ö”
assert_eq!(None, s.split_at_checked(16)); // Beyond the string length
1.80.0 · sourcepub fn split_at_mut_checked(
&mut self,
mid: usize,
) -> Option<(&mut str, &mut str)>
pub fn split_at_mut_checked( &mut self, mid: usize, ) -> Option<(&mut str, &mut str)>
Divides one mutable string slice into two at an index.
The argument, mid
, should be a valid byte offset from the start of the
string. It must also be on the boundary of a UTF-8 code point. The
method returns None
if that’s not the case.
The two slices returned go from the start of the string slice to mid
,
and from mid
to the end of the string slice.
To get immutable string slices instead, see the split_at_checked
method.
§Examples
let mut s = "Per Martin-Löf".to_string();
if let Some((first, last)) = s.split_at_mut_checked(3) {
first.make_ascii_uppercase();
assert_eq!("PER", first);
assert_eq!(" Martin-Löf", last);
}
assert_eq!("PER Martin-Löf", s);
assert_eq!(None, s.split_at_mut_checked(13)); // Inside “ö”
assert_eq!(None, s.split_at_mut_checked(16)); // Beyond the string length
1.0.0 · sourcepub fn chars(&self) -> Chars<'_> ⓘ
pub fn chars(&self) -> Chars<'_> ⓘ
Returns an iterator over the char
s of a string slice.
As a string slice consists of valid UTF-8, we can iterate through a
string slice by char
. This method returns such an iterator.
It’s important to remember that char
represents a Unicode Scalar
Value, and might not match your idea of what a ‘character’ is. Iteration
over grapheme clusters may be what you actually want. This functionality
is not provided by Rust’s standard library, check crates.io instead.
§Examples
Basic usage:
let word = "goodbye";
let count = word.chars().count();
assert_eq!(7, count);
let mut chars = word.chars();
assert_eq!(Some('g'), chars.next());
assert_eq!(Some('o'), chars.next());
assert_eq!(Some('o'), chars.next());
assert_eq!(Some('d'), chars.next());
assert_eq!(Some('b'), chars.next());
assert_eq!(Some('y'), chars.next());
assert_eq!(Some('e'), chars.next());
assert_eq!(None, chars.next());
Remember, char
s might not match your intuition about characters:
let y = "y̆";
let mut chars = y.chars();
assert_eq!(Some('y'), chars.next()); // not 'y̆'
assert_eq!(Some('\u{0306}'), chars.next());
assert_eq!(None, chars.next());
1.0.0 · sourcepub fn char_indices(&self) -> CharIndices<'_> ⓘ
pub fn char_indices(&self) -> CharIndices<'_> ⓘ
Returns an iterator over the char
s of a string slice, and their
positions.
As a string slice consists of valid UTF-8, we can iterate through a
string slice by char
. This method returns an iterator of both
these char
s, as well as their byte positions.
The iterator yields tuples. The position is first, the char
is
second.
§Examples
Basic usage:
let word = "goodbye";
let count = word.char_indices().count();
assert_eq!(7, count);
let mut char_indices = word.char_indices();
assert_eq!(Some((0, 'g')), char_indices.next());
assert_eq!(Some((1, 'o')), char_indices.next());
assert_eq!(Some((2, 'o')), char_indices.next());
assert_eq!(Some((3, 'd')), char_indices.next());
assert_eq!(Some((4, 'b')), char_indices.next());
assert_eq!(Some((5, 'y')), char_indices.next());
assert_eq!(Some((6, 'e')), char_indices.next());
assert_eq!(None, char_indices.next());
Remember, char
s might not match your intuition about characters:
let yes = "y̆es";
let mut char_indices = yes.char_indices();
assert_eq!(Some((0, 'y')), char_indices.next()); // not (0, 'y̆')
assert_eq!(Some((1, '\u{0306}')), char_indices.next());
// note the 3 here - the previous character took up two bytes
assert_eq!(Some((3, 'e')), char_indices.next());
assert_eq!(Some((4, 's')), char_indices.next());
assert_eq!(None, char_indices.next());
1.0.0 · sourcepub fn bytes(&self) -> Bytes<'_> ⓘ
pub fn bytes(&self) -> Bytes<'_> ⓘ
Returns an iterator over the bytes of a string slice.
As a string slice consists of a sequence of bytes, we can iterate through a string slice by byte. This method returns such an iterator.
§Examples
let mut bytes = "bors".bytes();
assert_eq!(Some(b'b'), bytes.next());
assert_eq!(Some(b'o'), bytes.next());
assert_eq!(Some(b'r'), bytes.next());
assert_eq!(Some(b's'), bytes.next());
assert_eq!(None, bytes.next());
1.1.0 · sourcepub fn split_whitespace(&self) -> SplitWhitespace<'_> ⓘ
pub fn split_whitespace(&self) -> SplitWhitespace<'_> ⓘ
Splits a string slice by whitespace.
The iterator returned will return string slices that are sub-slices of the original string slice, separated by any amount of whitespace.
‘Whitespace’ is defined according to the terms of the Unicode Derived
Core Property White_Space
. If you only want to split on ASCII whitespace
instead, use split_ascii_whitespace
.
§Examples
Basic usage:
let mut iter = "A few words".split_whitespace();
assert_eq!(Some("A"), iter.next());
assert_eq!(Some("few"), iter.next());
assert_eq!(Some("words"), iter.next());
assert_eq!(None, iter.next());
All kinds of whitespace are considered:
let mut iter = " Mary had\ta\u{2009}little \n\t lamb".split_whitespace();
assert_eq!(Some("Mary"), iter.next());
assert_eq!(Some("had"), iter.next());
assert_eq!(Some("a"), iter.next());
assert_eq!(Some("little"), iter.next());
assert_eq!(Some("lamb"), iter.next());
assert_eq!(None, iter.next());
If the string is empty or all whitespace, the iterator yields no string slices:
assert_eq!("".split_whitespace().next(), None);
assert_eq!(" ".split_whitespace().next(), None);
1.34.0 · sourcepub fn split_ascii_whitespace(&self) -> SplitAsciiWhitespace<'_> ⓘ
pub fn split_ascii_whitespace(&self) -> SplitAsciiWhitespace<'_> ⓘ
Splits a string slice by ASCII whitespace.
The iterator returned will return string slices that are sub-slices of the original string slice, separated by any amount of ASCII whitespace.
To split by Unicode Whitespace
instead, use split_whitespace
.
§Examples
Basic usage:
let mut iter = "A few words".split_ascii_whitespace();
assert_eq!(Some("A"), iter.next());
assert_eq!(Some("few"), iter.next());
assert_eq!(Some("words"), iter.next());
assert_eq!(None, iter.next());
All kinds of ASCII whitespace are considered:
let mut iter = " Mary had\ta little \n\t lamb".split_ascii_whitespace();
assert_eq!(Some("Mary"), iter.next());
assert_eq!(Some("had"), iter.next());
assert_eq!(Some("a"), iter.next());
assert_eq!(Some("little"), iter.next());
assert_eq!(Some("lamb"), iter.next());
assert_eq!(None, iter.next());
If the string is empty or all ASCII whitespace, the iterator yields no string slices:
assert_eq!("".split_ascii_whitespace().next(), None);
assert_eq!(" ".split_ascii_whitespace().next(), None);
1.0.0 · sourcepub fn lines(&self) -> Lines<'_> ⓘ
pub fn lines(&self) -> Lines<'_> ⓘ
Returns an iterator over the lines of a string, as string slices.
Lines are split at line endings that are either newlines (\n
) or
sequences of a carriage return followed by a line feed (\r\n
).
Line terminators are not included in the lines returned by the iterator.
Note that any carriage return (\r
) not immediately followed by a
line feed (\n
) does not split a line. These carriage returns are
thereby included in the produced lines.
The final line ending is optional. A string that ends with a final line ending will return the same lines as an otherwise identical string without a final line ending.
§Examples
Basic usage:
let text = "foo\r\nbar\n\nbaz\r";
let mut lines = text.lines();
assert_eq!(Some("foo"), lines.next());
assert_eq!(Some("bar"), lines.next());
assert_eq!(Some(""), lines.next());
// Trailing carriage return is included in the last line
assert_eq!(Some("baz\r"), lines.next());
assert_eq!(None, lines.next());
The final line does not require any ending:
let text = "foo\nbar\n\r\nbaz";
let mut lines = text.lines();
assert_eq!(Some("foo"), lines.next());
assert_eq!(Some("bar"), lines.next());
assert_eq!(Some(""), lines.next());
assert_eq!(Some("baz"), lines.next());
assert_eq!(None, lines.next());
1.0.0 · sourcepub fn lines_any(&self) -> LinesAny<'_> ⓘ
👎Deprecated since 1.4.0: use lines() instead now
pub fn lines_any(&self) -> LinesAny<'_> ⓘ
Returns an iterator over the lines of a string.
1.8.0 · sourcepub fn encode_utf16(&self) -> EncodeUtf16<'_> ⓘ
pub fn encode_utf16(&self) -> EncodeUtf16<'_> ⓘ
Returns an iterator of u16
over the string encoded as UTF-16.
§Examples
let text = "Zażółć gęślą jaźń";
let utf8_len = text.len();
let utf16_len = text.encode_utf16().count();
assert!(utf16_len <= utf8_len);
1.0.0 · sourcepub fn contains<P>(&self, pat: P) -> boolwhere
P: Pattern,
pub fn contains<P>(&self, pat: P) -> boolwhere
P: Pattern,
Returns true
if the given pattern matches a sub-slice of
this string slice.
Returns false
if it does not.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Examples
let bananas = "bananas";
assert!(bananas.contains("nana"));
assert!(!bananas.contains("apples"));
1.0.0 · sourcepub fn starts_with<P>(&self, pat: P) -> boolwhere
P: Pattern,
pub fn starts_with<P>(&self, pat: P) -> boolwhere
P: Pattern,
Returns true
if the given pattern matches a prefix of this
string slice.
Returns false
if it does not.
The pattern can be a &str
, in which case this function will return true if
the &str
is a prefix of this string slice.
The pattern can also be a char
, a slice of char
s, or a
function or closure that determines if a character matches.
These will only be checked against the first character of this string slice.
Look at the second example below regarding behavior for slices of char
s.
§Examples
let bananas = "bananas";
assert!(bananas.starts_with("bana"));
assert!(!bananas.starts_with("nana"));
let bananas = "bananas";
// Note that both of these assert successfully.
assert!(bananas.starts_with(&['b', 'a', 'n', 'a']));
assert!(bananas.starts_with(&['a', 'b', 'c', 'd']));
1.0.0 · sourcepub fn ends_with<P>(&self, pat: P) -> bool
pub fn ends_with<P>(&self, pat: P) -> bool
Returns true
if the given pattern matches a suffix of this
string slice.
Returns false
if it does not.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Examples
let bananas = "bananas";
assert!(bananas.ends_with("anas"));
assert!(!bananas.ends_with("nana"));
1.0.0 · sourcepub fn find<P>(&self, pat: P) -> Option<usize>where
P: Pattern,
pub fn find<P>(&self, pat: P) -> Option<usize>where
P: Pattern,
Returns the byte index of the first character of this string slice that matches the pattern.
Returns None
if the pattern doesn’t match.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Examples
Simple patterns:
let s = "Löwe 老虎 Léopard Gepardi";
assert_eq!(s.find('L'), Some(0));
assert_eq!(s.find('é'), Some(14));
assert_eq!(s.find("pard"), Some(17));
More complex patterns using point-free style and closures:
let s = "Löwe 老虎 Léopard";
assert_eq!(s.find(char::is_whitespace), Some(5));
assert_eq!(s.find(char::is_lowercase), Some(1));
assert_eq!(s.find(|c: char| c.is_whitespace() || c.is_lowercase()), Some(1));
assert_eq!(s.find(|c: char| (c < 'o') && (c > 'a')), Some(4));
Not finding the pattern:
let s = "Löwe 老虎 Léopard";
let x: &[_] = &['1', '2'];
assert_eq!(s.find(x), None);
1.0.0 · sourcepub fn rfind<P>(&self, pat: P) -> Option<usize>
pub fn rfind<P>(&self, pat: P) -> Option<usize>
Returns the byte index for the first character of the last match of the pattern in this string slice.
Returns None
if the pattern doesn’t match.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Examples
Simple patterns:
let s = "Löwe 老虎 Léopard Gepardi";
assert_eq!(s.rfind('L'), Some(13));
assert_eq!(s.rfind('é'), Some(14));
assert_eq!(s.rfind("pard"), Some(24));
More complex patterns with closures:
let s = "Löwe 老虎 Léopard";
assert_eq!(s.rfind(char::is_whitespace), Some(12));
assert_eq!(s.rfind(char::is_lowercase), Some(20));
Not finding the pattern:
let s = "Löwe 老虎 Léopard";
let x: &[_] = &['1', '2'];
assert_eq!(s.rfind(x), None);
1.0.0 · sourcepub fn split<P>(&self, pat: P) -> Split<'_, P> ⓘwhere
P: Pattern,
pub fn split<P>(&self, pat: P) -> Split<'_, P> ⓘwhere
P: Pattern,
Returns an iterator over substrings of this string slice, separated by characters matched by a pattern.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern
allows a reverse search and forward/reverse search yields the same
elements. This is true for, e.g., char
, but not for &str
.
If the pattern allows a reverse search but its results might differ
from a forward search, the rsplit
method can be used.
§Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lamb".split(' ').collect();
assert_eq!(v, ["Mary", "had", "a", "little", "lamb"]);
let v: Vec<&str> = "".split('X').collect();
assert_eq!(v, [""]);
let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect();
assert_eq!(v, ["lion", "", "tiger", "leopard"]);
let v: Vec<&str> = "lion::tiger::leopard".split("::").collect();
assert_eq!(v, ["lion", "tiger", "leopard"]);
let v: Vec<&str> = "abc1def2ghi".split(char::is_numeric).collect();
assert_eq!(v, ["abc", "def", "ghi"]);
let v: Vec<&str> = "lionXtigerXleopard".split(char::is_uppercase).collect();
assert_eq!(v, ["lion", "tiger", "leopard"]);
If the pattern is a slice of chars, split on each occurrence of any of the characters:
let v: Vec<&str> = "2020-11-03 23:59".split(&['-', ' ', ':', '@'][..]).collect();
assert_eq!(v, ["2020", "11", "03", "23", "59"]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect();
assert_eq!(v, ["abc", "def", "ghi"]);
If a string contains multiple contiguous separators, you will end up with empty strings in the output:
let x = "||||a||b|c".to_string();
let d: Vec<_> = x.split('|').collect();
assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
Contiguous separators are separated by the empty string.
let x = "(///)".to_string();
let d: Vec<_> = x.split('/').collect();
assert_eq!(d, &["(", "", "", ")"]);
Separators at the start or end of a string are neighbored by empty strings.
let d: Vec<_> = "010".split("0").collect();
assert_eq!(d, &["", "1", ""]);
When the empty string is used as a separator, it separates every character in the string, along with the beginning and end of the string.
let f: Vec<_> = "rust".split("").collect();
assert_eq!(f, &["", "r", "u", "s", "t", ""]);
Contiguous separators can lead to possibly surprising behavior when whitespace is used as the separator. This code is correct:
let x = " a b c".to_string();
let d: Vec<_> = x.split(' ').collect();
assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
It does not give you:
assert_eq!(d, &["a", "b", "c"]);
Use split_whitespace
for this behavior.
1.51.0 · sourcepub fn split_inclusive<P>(&self, pat: P) -> SplitInclusive<'_, P> ⓘwhere
P: Pattern,
pub fn split_inclusive<P>(&self, pat: P) -> SplitInclusive<'_, P> ⓘwhere
P: Pattern,
Returns an iterator over substrings of this string slice, separated by characters matched by a pattern.
Differs from the iterator produced by split
in that split_inclusive
leaves the matched part as the terminator of the substring.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Examples
let v: Vec<&str> = "Mary had a little lamb\nlittle lamb\nlittle lamb."
.split_inclusive('\n').collect();
assert_eq!(v, ["Mary had a little lamb\n", "little lamb\n", "little lamb."]);
If the last element of the string is matched, that element will be considered the terminator of the preceding substring. That substring will be the last item returned by the iterator.
let v: Vec<&str> = "Mary had a little lamb\nlittle lamb\nlittle lamb.\n"
.split_inclusive('\n').collect();
assert_eq!(v, ["Mary had a little lamb\n", "little lamb\n", "little lamb.\n"]);
1.0.0 · sourcepub fn rsplit<P>(&self, pat: P) -> RSplit<'_, P> ⓘ
pub fn rsplit<P>(&self, pat: P) -> RSplit<'_, P> ⓘ
Returns an iterator over substrings of the given string slice, separated by characters matched by a pattern and yielded in reverse order.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator requires that the pattern supports a reverse
search, and it will be a DoubleEndedIterator
if a forward/reverse
search yields the same elements.
For iterating from the front, the split
method can be used.
§Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lamb".rsplit(' ').collect();
assert_eq!(v, ["lamb", "little", "a", "had", "Mary"]);
let v: Vec<&str> = "".rsplit('X').collect();
assert_eq!(v, [""]);
let v: Vec<&str> = "lionXXtigerXleopard".rsplit('X').collect();
assert_eq!(v, ["leopard", "tiger", "", "lion"]);
let v: Vec<&str> = "lion::tiger::leopard".rsplit("::").collect();
assert_eq!(v, ["leopard", "tiger", "lion"]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect();
assert_eq!(v, ["ghi", "def", "abc"]);
1.0.0 · sourcepub fn split_terminator<P>(&self, pat: P) -> SplitTerminator<'_, P> ⓘwhere
P: Pattern,
pub fn split_terminator<P>(&self, pat: P) -> SplitTerminator<'_, P> ⓘwhere
P: Pattern,
Returns an iterator over substrings of the given string slice, separated by characters matched by a pattern.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
Equivalent to split
, except that the trailing substring
is skipped if empty.
This method can be used for string data that is terminated, rather than separated by a pattern.
§Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern
allows a reverse search and forward/reverse search yields the same
elements. This is true for, e.g., char
, but not for &str
.
If the pattern allows a reverse search but its results might differ
from a forward search, the rsplit_terminator
method can be used.
§Examples
let v: Vec<&str> = "A.B.".split_terminator('.').collect();
assert_eq!(v, ["A", "B"]);
let v: Vec<&str> = "A..B..".split_terminator(".").collect();
assert_eq!(v, ["A", "", "B", ""]);
let v: Vec<&str> = "A.B:C.D".split_terminator(&['.', ':'][..]).collect();
assert_eq!(v, ["A", "B", "C", "D"]);
1.0.0 · sourcepub fn rsplit_terminator<P>(&self, pat: P) -> RSplitTerminator<'_, P> ⓘ
pub fn rsplit_terminator<P>(&self, pat: P) -> RSplitTerminator<'_, P> ⓘ
Returns an iterator over substrings of self
, separated by characters
matched by a pattern and yielded in reverse order.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
Equivalent to split
, except that the trailing substring is
skipped if empty.
This method can be used for string data that is terminated, rather than separated by a pattern.
§Iterator behavior
The returned iterator requires that the pattern supports a reverse search, and it will be double ended if a forward/reverse search yields the same elements.
For iterating from the front, the split_terminator
method can be
used.
§Examples
let v: Vec<&str> = "A.B.".rsplit_terminator('.').collect();
assert_eq!(v, ["B", "A"]);
let v: Vec<&str> = "A..B..".rsplit_terminator(".").collect();
assert_eq!(v, ["", "B", "", "A"]);
let v: Vec<&str> = "A.B:C.D".rsplit_terminator(&['.', ':'][..]).collect();
assert_eq!(v, ["D", "C", "B", "A"]);
1.0.0 · sourcepub fn splitn<P>(&self, n: usize, pat: P) -> SplitN<'_, P> ⓘwhere
P: Pattern,
pub fn splitn<P>(&self, n: usize, pat: P) -> SplitN<'_, P> ⓘwhere
P: Pattern,
Returns an iterator over substrings of the given string slice, separated
by a pattern, restricted to returning at most n
items.
If n
substrings are returned, the last substring (the n
th substring)
will contain the remainder of the string.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator will not be double ended, because it is not efficient to support.
If the pattern allows a reverse search, the rsplitn
method can be
used.
§Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lambda".splitn(3, ' ').collect();
assert_eq!(v, ["Mary", "had", "a little lambda"]);
let v: Vec<&str> = "lionXXtigerXleopard".splitn(3, "X").collect();
assert_eq!(v, ["lion", "", "tigerXleopard"]);
let v: Vec<&str> = "abcXdef".splitn(1, 'X').collect();
assert_eq!(v, ["abcXdef"]);
let v: Vec<&str> = "".splitn(1, 'X').collect();
assert_eq!(v, [""]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect();
assert_eq!(v, ["abc", "defXghi"]);
1.0.0 · sourcepub fn rsplitn<P>(&self, n: usize, pat: P) -> RSplitN<'_, P> ⓘ
pub fn rsplitn<P>(&self, n: usize, pat: P) -> RSplitN<'_, P> ⓘ
Returns an iterator over substrings of this string slice, separated by a
pattern, starting from the end of the string, restricted to returning at
most n
items.
If n
substrings are returned, the last substring (the n
th substring)
will contain the remainder of the string.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator will not be double ended, because it is not efficient to support.
For splitting from the front, the splitn
method can be used.
§Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lamb".rsplitn(3, ' ').collect();
assert_eq!(v, ["lamb", "little", "Mary had a"]);
let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(3, 'X').collect();
assert_eq!(v, ["leopard", "tiger", "lionX"]);
let v: Vec<&str> = "lion::tiger::leopard".rsplitn(2, "::").collect();
assert_eq!(v, ["leopard", "lion::tiger"]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect();
assert_eq!(v, ["ghi", "abc1def"]);
1.52.0 · sourcepub fn split_once<P>(&self, delimiter: P) -> Option<(&str, &str)>where
P: Pattern,
pub fn split_once<P>(&self, delimiter: P) -> Option<(&str, &str)>where
P: Pattern,
Splits the string on the first occurrence of the specified delimiter and returns prefix before delimiter and suffix after delimiter.
§Examples
assert_eq!("cfg".split_once('='), None);
assert_eq!("cfg=".split_once('='), Some(("cfg", "")));
assert_eq!("cfg=foo".split_once('='), Some(("cfg", "foo")));
assert_eq!("cfg=foo=bar".split_once('='), Some(("cfg", "foo=bar")));
1.52.0 · sourcepub fn rsplit_once<P>(&self, delimiter: P) -> Option<(&str, &str)>
pub fn rsplit_once<P>(&self, delimiter: P) -> Option<(&str, &str)>
Splits the string on the last occurrence of the specified delimiter and returns prefix before delimiter and suffix after delimiter.
§Examples
assert_eq!("cfg".rsplit_once('='), None);
assert_eq!("cfg=foo".rsplit_once('='), Some(("cfg", "foo")));
assert_eq!("cfg=foo=bar".rsplit_once('='), Some(("cfg=foo", "bar")));
1.2.0 · sourcepub fn matches<P>(&self, pat: P) -> Matches<'_, P> ⓘwhere
P: Pattern,
pub fn matches<P>(&self, pat: P) -> Matches<'_, P> ⓘwhere
P: Pattern,
Returns an iterator over the disjoint matches of a pattern within the given string slice.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern
allows a reverse search and forward/reverse search yields the same
elements. This is true for, e.g., char
, but not for &str
.
If the pattern allows a reverse search but its results might differ
from a forward search, the rmatches
method can be used.
§Examples
let v: Vec<&str> = "abcXXXabcYYYabc".matches("abc").collect();
assert_eq!(v, ["abc", "abc", "abc"]);
let v: Vec<&str> = "1abc2abc3".matches(char::is_numeric).collect();
assert_eq!(v, ["1", "2", "3"]);
1.2.0 · sourcepub fn rmatches<P>(&self, pat: P) -> RMatches<'_, P> ⓘ
pub fn rmatches<P>(&self, pat: P) -> RMatches<'_, P> ⓘ
Returns an iterator over the disjoint matches of a pattern within this string slice, yielded in reverse order.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator requires that the pattern supports a reverse
search, and it will be a DoubleEndedIterator
if a forward/reverse
search yields the same elements.
For iterating from the front, the matches
method can be used.
§Examples
let v: Vec<&str> = "abcXXXabcYYYabc".rmatches("abc").collect();
assert_eq!(v, ["abc", "abc", "abc"]);
let v: Vec<&str> = "1abc2abc3".rmatches(char::is_numeric).collect();
assert_eq!(v, ["3", "2", "1"]);
1.5.0 · sourcepub fn match_indices<P>(&self, pat: P) -> MatchIndices<'_, P> ⓘwhere
P: Pattern,
pub fn match_indices<P>(&self, pat: P) -> MatchIndices<'_, P> ⓘwhere
P: Pattern,
Returns an iterator over the disjoint matches of a pattern within this string slice as well as the index that the match starts at.
For matches of pat
within self
that overlap, only the indices
corresponding to the first match are returned.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern
allows a reverse search and forward/reverse search yields the same
elements. This is true for, e.g., char
, but not for &str
.
If the pattern allows a reverse search but its results might differ
from a forward search, the rmatch_indices
method can be used.
§Examples
let v: Vec<_> = "abcXXXabcYYYabc".match_indices("abc").collect();
assert_eq!(v, [(0, "abc"), (6, "abc"), (12, "abc")]);
let v: Vec<_> = "1abcabc2".match_indices("abc").collect();
assert_eq!(v, [(1, "abc"), (4, "abc")]);
let v: Vec<_> = "ababa".match_indices("aba").collect();
assert_eq!(v, [(0, "aba")]); // only the first `aba`
1.5.0 · sourcepub fn rmatch_indices<P>(&self, pat: P) -> RMatchIndices<'_, P> ⓘ
pub fn rmatch_indices<P>(&self, pat: P) -> RMatchIndices<'_, P> ⓘ
Returns an iterator over the disjoint matches of a pattern within self
,
yielded in reverse order along with the index of the match.
For matches of pat
within self
that overlap, only the indices
corresponding to the last match are returned.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Iterator behavior
The returned iterator requires that the pattern supports a reverse
search, and it will be a DoubleEndedIterator
if a forward/reverse
search yields the same elements.
For iterating from the front, the match_indices
method can be used.
§Examples
let v: Vec<_> = "abcXXXabcYYYabc".rmatch_indices("abc").collect();
assert_eq!(v, [(12, "abc"), (6, "abc"), (0, "abc")]);
let v: Vec<_> = "1abcabc2".rmatch_indices("abc").collect();
assert_eq!(v, [(4, "abc"), (1, "abc")]);
let v: Vec<_> = "ababa".rmatch_indices("aba").collect();
assert_eq!(v, [(2, "aba")]); // only the last `aba`
1.0.0 · sourcepub fn trim(&self) -> &str
pub fn trim(&self) -> &str
Returns a string slice with leading and trailing whitespace removed.
‘Whitespace’ is defined according to the terms of the Unicode Derived
Core Property White_Space
, which includes newlines.
§Examples
let s = "\n Hello\tworld\t\n";
assert_eq!("Hello\tworld", s.trim());
1.30.0 · sourcepub fn trim_start(&self) -> &str
pub fn trim_start(&self) -> &str
Returns a string slice with leading whitespace removed.
‘Whitespace’ is defined according to the terms of the Unicode Derived
Core Property White_Space
, which includes newlines.
§Text directionality
A string is a sequence of bytes. start
in this context means the first
position of that byte string; for a left-to-right language like English or
Russian, this will be left side, and for right-to-left languages like
Arabic or Hebrew, this will be the right side.
§Examples
Basic usage:
let s = "\n Hello\tworld\t\n";
assert_eq!("Hello\tworld\t\n", s.trim_start());
Directionality:
let s = " English ";
assert!(Some('E') == s.trim_start().chars().next());
let s = " עברית ";
assert!(Some('ע') == s.trim_start().chars().next());
1.30.0 · sourcepub fn trim_end(&self) -> &str
pub fn trim_end(&self) -> &str
Returns a string slice with trailing whitespace removed.
‘Whitespace’ is defined according to the terms of the Unicode Derived
Core Property White_Space
, which includes newlines.
§Text directionality
A string is a sequence of bytes. end
in this context means the last
position of that byte string; for a left-to-right language like English or
Russian, this will be right side, and for right-to-left languages like
Arabic or Hebrew, this will be the left side.
§Examples
Basic usage:
let s = "\n Hello\tworld\t\n";
assert_eq!("\n Hello\tworld", s.trim_end());
Directionality:
let s = " English ";
assert!(Some('h') == s.trim_end().chars().rev().next());
let s = " עברית ";
assert!(Some('ת') == s.trim_end().chars().rev().next());
1.0.0 · sourcepub fn trim_left(&self) -> &str
👎Deprecated since 1.33.0: superseded by trim_start
pub fn trim_left(&self) -> &str
trim_start
Returns a string slice with leading whitespace removed.
‘Whitespace’ is defined according to the terms of the Unicode Derived
Core Property White_Space
.
§Text directionality
A string is a sequence of bytes. ‘Left’ in this context means the first position of that byte string; for a language like Arabic or Hebrew which are ‘right to left’ rather than ‘left to right’, this will be the right side, not the left.
§Examples
Basic usage:
let s = " Hello\tworld\t";
assert_eq!("Hello\tworld\t", s.trim_left());
Directionality:
let s = " English";
assert!(Some('E') == s.trim_left().chars().next());
let s = " עברית";
assert!(Some('ע') == s.trim_left().chars().next());
1.0.0 · sourcepub fn trim_right(&self) -> &str
👎Deprecated since 1.33.0: superseded by trim_end
pub fn trim_right(&self) -> &str
trim_end
Returns a string slice with trailing whitespace removed.
‘Whitespace’ is defined according to the terms of the Unicode Derived
Core Property White_Space
.
§Text directionality
A string is a sequence of bytes. ‘Right’ in this context means the last position of that byte string; for a language like Arabic or Hebrew which are ‘right to left’ rather than ‘left to right’, this will be the left side, not the right.
§Examples
Basic usage:
let s = " Hello\tworld\t";
assert_eq!(" Hello\tworld", s.trim_right());
Directionality:
let s = "English ";
assert!(Some('h') == s.trim_right().chars().rev().next());
let s = "עברית ";
assert!(Some('ת') == s.trim_right().chars().rev().next());
1.0.0 · sourcepub fn trim_matches<P>(&self, pat: P) -> &str
pub fn trim_matches<P>(&self, pat: P) -> &str
Returns a string slice with all prefixes and suffixes that match a pattern repeatedly removed.
The pattern can be a char
, a slice of char
s, or a function
or closure that determines if a character matches.
§Examples
Simple patterns:
assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar");
assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar");
let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_matches(x), "foo1bar");
A more complex pattern, using a closure:
assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar");
1.30.0 · sourcepub fn trim_start_matches<P>(&self, pat: P) -> &strwhere
P: Pattern,
pub fn trim_start_matches<P>(&self, pat: P) -> &strwhere
P: Pattern,
Returns a string slice with all prefixes that match a pattern repeatedly removed.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Text directionality
A string is a sequence of bytes. start
in this context means the first
position of that byte string; for a left-to-right language like English or
Russian, this will be left side, and for right-to-left languages like
Arabic or Hebrew, this will be the right side.
§Examples
assert_eq!("11foo1bar11".trim_start_matches('1'), "foo1bar11");
assert_eq!("123foo1bar123".trim_start_matches(char::is_numeric), "foo1bar123");
let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_start_matches(x), "foo1bar12");
1.45.0 · sourcepub fn strip_prefix<P>(&self, prefix: P) -> Option<&str>where
P: Pattern,
pub fn strip_prefix<P>(&self, prefix: P) -> Option<&str>where
P: Pattern,
Returns a string slice with the prefix removed.
If the string starts with the pattern prefix
, returns the substring after the prefix,
wrapped in Some
. Unlike trim_start_matches
, this method removes the prefix exactly once.
If the string does not start with prefix
, returns None
.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Examples
assert_eq!("foo:bar".strip_prefix("foo:"), Some("bar"));
assert_eq!("foo:bar".strip_prefix("bar"), None);
assert_eq!("foofoo".strip_prefix("foo"), Some("foo"));
1.45.0 · sourcepub fn strip_suffix<P>(&self, suffix: P) -> Option<&str>
pub fn strip_suffix<P>(&self, suffix: P) -> Option<&str>
Returns a string slice with the suffix removed.
If the string ends with the pattern suffix
, returns the substring before the suffix,
wrapped in Some
. Unlike trim_end_matches
, this method removes the suffix exactly once.
If the string does not end with suffix
, returns None
.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Examples
assert_eq!("bar:foo".strip_suffix(":foo"), Some("bar"));
assert_eq!("bar:foo".strip_suffix("bar"), None);
assert_eq!("foofoo".strip_suffix("foo"), Some("foo"));
1.30.0 · sourcepub fn trim_end_matches<P>(&self, pat: P) -> &str
pub fn trim_end_matches<P>(&self, pat: P) -> &str
Returns a string slice with all suffixes that match a pattern repeatedly removed.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Text directionality
A string is a sequence of bytes. end
in this context means the last
position of that byte string; for a left-to-right language like English or
Russian, this will be right side, and for right-to-left languages like
Arabic or Hebrew, this will be the left side.
§Examples
Simple patterns:
assert_eq!("11foo1bar11".trim_end_matches('1'), "11foo1bar");
assert_eq!("123foo1bar123".trim_end_matches(char::is_numeric), "123foo1bar");
let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_end_matches(x), "12foo1bar");
A more complex pattern, using a closure:
assert_eq!("1fooX".trim_end_matches(|c| c == '1' || c == 'X'), "1foo");
1.0.0 · sourcepub fn trim_left_matches<P>(&self, pat: P) -> &strwhere
P: Pattern,
👎Deprecated since 1.33.0: superseded by trim_start_matches
pub fn trim_left_matches<P>(&self, pat: P) -> &strwhere
P: Pattern,
trim_start_matches
Returns a string slice with all prefixes that match a pattern repeatedly removed.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Text directionality
A string is a sequence of bytes. ‘Left’ in this context means the first position of that byte string; for a language like Arabic or Hebrew which are ‘right to left’ rather than ‘left to right’, this will be the right side, not the left.
§Examples
assert_eq!("11foo1bar11".trim_left_matches('1'), "foo1bar11");
assert_eq!("123foo1bar123".trim_left_matches(char::is_numeric), "foo1bar123");
let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_left_matches(x), "foo1bar12");
1.0.0 · sourcepub fn trim_right_matches<P>(&self, pat: P) -> &str
👎Deprecated since 1.33.0: superseded by trim_end_matches
pub fn trim_right_matches<P>(&self, pat: P) -> &str
trim_end_matches
Returns a string slice with all suffixes that match a pattern repeatedly removed.
The pattern can be a &str
, char
, a slice of char
s, or a
function or closure that determines if a character matches.
§Text directionality
A string is a sequence of bytes. ‘Right’ in this context means the last position of that byte string; for a language like Arabic or Hebrew which are ‘right to left’ rather than ‘left to right’, this will be the left side, not the right.
§Examples
Simple patterns:
assert_eq!("11foo1bar11".trim_right_matches('1'), "11foo1bar");
assert_eq!("123foo1bar123".trim_right_matches(char::is_numeric), "123foo1bar");
let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_right_matches(x), "12foo1bar");
A more complex pattern, using a closure:
assert_eq!("1fooX".trim_right_matches(|c| c == '1' || c == 'X'), "1foo");
1.0.0 · sourcepub fn parse<F>(&self) -> Result<F, <F as FromStr>::Err>where
F: FromStr,
pub fn parse<F>(&self) -> Result<F, <F as FromStr>::Err>where
F: FromStr,
Parses this string slice into another type.
Because parse
is so general, it can cause problems with type
inference. As such, parse
is one of the few times you’ll see
the syntax affectionately known as the ‘turbofish’: ::<>
. This
helps the inference algorithm understand specifically which type
you’re trying to parse into.
parse
can parse into any type that implements the FromStr
trait.
§Errors
Will return Err
if it’s not possible to parse this string slice into
the desired type.
§Examples
Basic usage
let four: u32 = "4".parse().unwrap();
assert_eq!(4, four);
Using the ‘turbofish’ instead of annotating four
:
let four = "4".parse::<u32>();
assert_eq!(Ok(4), four);
Failing to parse:
let nope = "j".parse::<u32>();
assert!(nope.is_err());
1.23.0 · sourcepub fn is_ascii(&self) -> bool
pub fn is_ascii(&self) -> bool
Checks if all characters in this string are within the ASCII range.
§Examples
let ascii = "hello!\n";
let non_ascii = "Grüße, Jürgen ❤";
assert!(ascii.is_ascii());
assert!(!non_ascii.is_ascii());
sourcepub fn as_ascii(&self) -> Option<&[AsciiChar]>
🔬This is a nightly-only experimental API. (ascii_char
)
pub fn as_ascii(&self) -> Option<&[AsciiChar]>
ascii_char
)If this string slice is_ascii
, returns it as a slice
of ASCII characters, otherwise returns None
.
1.23.0 · sourcepub fn eq_ignore_ascii_case(&self, other: &str) -> bool
pub fn eq_ignore_ascii_case(&self, other: &str) -> bool
Checks that two strings are an ASCII case-insensitive match.
Same as to_ascii_lowercase(a) == to_ascii_lowercase(b)
,
but without allocating and copying temporaries.
§Examples
assert!("Ferris".eq_ignore_ascii_case("FERRIS"));
assert!("Ferrös".eq_ignore_ascii_case("FERRöS"));
assert!(!"Ferrös".eq_ignore_ascii_case("FERRÖS"));
1.23.0 · sourcepub fn make_ascii_uppercase(&mut self)
pub fn make_ascii_uppercase(&mut self)
Converts this string to its ASCII upper case equivalent in-place.
ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.
To return a new uppercased value without modifying the existing one, use
to_ascii_uppercase()
.
§Examples
let mut s = String::from("Grüße, Jürgen ❤");
s.make_ascii_uppercase();
assert_eq!("GRüßE, JüRGEN ❤", s);
1.23.0 · sourcepub fn make_ascii_lowercase(&mut self)
pub fn make_ascii_lowercase(&mut self)
Converts this string to its ASCII lower case equivalent in-place.
ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.
To return a new lowercased value without modifying the existing one, use
to_ascii_lowercase()
.
§Examples
let mut s = String::from("GRÜßE, JÜRGEN ❤");
s.make_ascii_lowercase();
assert_eq!("grÜße, jÜrgen ❤", s);
1.80.0 · sourcepub fn trim_ascii_start(&self) -> &str
pub fn trim_ascii_start(&self) -> &str
Returns a string slice with leading ASCII whitespace removed.
‘Whitespace’ refers to the definition used by
u8::is_ascii_whitespace
.
§Examples
assert_eq!(" \t \u{3000}hello world\n".trim_ascii_start(), "\u{3000}hello world\n");
assert_eq!(" ".trim_ascii_start(), "");
assert_eq!("".trim_ascii_start(), "");
1.80.0 · sourcepub fn trim_ascii_end(&self) -> &str
pub fn trim_ascii_end(&self) -> &str
Returns a string slice with trailing ASCII whitespace removed.
‘Whitespace’ refers to the definition used by
u8::is_ascii_whitespace
.
§Examples
assert_eq!("\r hello world\u{3000}\n ".trim_ascii_end(), "\r hello world\u{3000}");
assert_eq!(" ".trim_ascii_end(), "");
assert_eq!("".trim_ascii_end(), "");
1.80.0 · sourcepub fn trim_ascii(&self) -> &str
pub fn trim_ascii(&self) -> &str
Returns a string slice with leading and trailing ASCII whitespace removed.
‘Whitespace’ refers to the definition used by
u8::is_ascii_whitespace
.
§Examples
assert_eq!("\r hello world\n ".trim_ascii(), "hello world");
assert_eq!(" ".trim_ascii(), "");
assert_eq!("".trim_ascii(), "");
1.34.0 · sourcepub fn escape_debug(&self) -> EscapeDebug<'_> ⓘ
pub fn escape_debug(&self) -> EscapeDebug<'_> ⓘ
Returns an iterator that escapes each char in self
with char::escape_debug
.
Note: only extended grapheme codepoints that begin the string will be escaped.
§Examples
As an iterator:
for c in "❤\n!".escape_debug() {
print!("{c}");
}
println!();
Using println!
directly:
println!("{}", "❤\n!".escape_debug());
Both are equivalent to:
println!("❤\\n!");
Using to_string
:
assert_eq!("❤\n!".escape_debug().to_string(), "❤\\n!");
1.34.0 · sourcepub fn escape_default(&self) -> EscapeDefault<'_> ⓘ
pub fn escape_default(&self) -> EscapeDefault<'_> ⓘ
Returns an iterator that escapes each char in self
with char::escape_default
.
§Examples
As an iterator:
for c in "❤\n!".escape_default() {
print!("{c}");
}
println!();
Using println!
directly:
println!("{}", "❤\n!".escape_default());
Both are equivalent to:
println!("\\u{{2764}}\\n!");
Using to_string
:
assert_eq!("❤\n!".escape_default().to_string(), "\\u{2764}\\n!");
1.34.0 · sourcepub fn escape_unicode(&self) -> EscapeUnicode<'_> ⓘ
pub fn escape_unicode(&self) -> EscapeUnicode<'_> ⓘ
Returns an iterator that escapes each char in self
with char::escape_unicode
.
§Examples
As an iterator:
for c in "❤\n!".escape_unicode() {
print!("{c}");
}
println!();
Using println!
directly:
println!("{}", "❤\n!".escape_unicode());
Both are equivalent to:
println!("\\u{{2764}}\\u{{a}}\\u{{21}}");
Using to_string
:
assert_eq!("❤\n!".escape_unicode().to_string(), "\\u{2764}\\u{a}\\u{21}");
sourcepub fn substr_range(&self, substr: &str) -> Option<Range<usize>>
🔬This is a nightly-only experimental API. (substr_range
)
pub fn substr_range(&self, substr: &str) -> Option<Range<usize>>
substr_range
)Returns the range that a substring points to.
Returns None
if substr
does not point within self
.
Unlike str::find
, this does not search through the string.
Instead, it uses pointer arithmetic to find where in the string
substr
is derived from.
This is useful for extending str::split
and similar methods.
Note that this method may return false positives (typically either
Some(0..0)
or Some(self.len()..self.len())
) if substr
is a
zero-length str
that points at the beginning or end of another,
independent, str
.
§Examples
#![feature(substr_range)]
let data = "a, b, b, a";
let mut iter = data.split(", ").map(|s| data.substr_range(s).unwrap());
assert_eq!(iter.next(), Some(0..1));
assert_eq!(iter.next(), Some(3..4));
assert_eq!(iter.next(), Some(6..7));
assert_eq!(iter.next(), Some(9..10));
1.0.0 · sourcepub fn replace<P>(&self, from: P, to: &str) -> Stringwhere
P: Pattern,
pub fn replace<P>(&self, from: P, to: &str) -> Stringwhere
P: Pattern,
Replaces all matches of a pattern with another string.
replace
creates a new String
, and copies the data from this string slice into it.
While doing so, it attempts to find matches of a pattern. If it finds any, it
replaces them with the replacement string slice.
§Examples
Basic usage:
let s = "this is old";
assert_eq!("this is new", s.replace("old", "new"));
assert_eq!("than an old", s.replace("is", "an"));
When the pattern doesn’t match, it returns this string slice as String
:
let s = "this is old";
assert_eq!(s, s.replace("cookie monster", "little lamb"));
1.16.0 · sourcepub fn replacen<P>(&self, pat: P, to: &str, count: usize) -> Stringwhere
P: Pattern,
pub fn replacen<P>(&self, pat: P, to: &str, count: usize) -> Stringwhere
P: Pattern,
Replaces first N matches of a pattern with another string.
replacen
creates a new String
, and copies the data from this string slice into it.
While doing so, it attempts to find matches of a pattern. If it finds any, it
replaces them with the replacement string slice at most count
times.
§Examples
Basic usage:
let s = "foo foo 123 foo";
assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
When the pattern doesn’t match, it returns this string slice as String
:
let s = "this is old";
assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
1.2.0 · sourcepub fn to_lowercase(&self) -> String
pub fn to_lowercase(&self) -> String
Returns the lowercase equivalent of this string slice, as a new String
.
‘Lowercase’ is defined according to the terms of the Unicode Derived Core Property
Lowercase
.
Since some characters can expand into multiple characters when changing
the case, this function returns a String
instead of modifying the
parameter in-place.
§Examples
Basic usage:
let s = "HELLO";
assert_eq!("hello", s.to_lowercase());
A tricky example, with sigma:
let sigma = "Σ";
assert_eq!("σ", sigma.to_lowercase());
// but at the end of a word, it's ς, not σ:
let odysseus = "ὈΔΥΣΣΕΎΣ";
assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
Languages without case are not changed:
let new_year = "农历新年";
assert_eq!(new_year, new_year.to_lowercase());
1.2.0 · sourcepub fn to_uppercase(&self) -> String
pub fn to_uppercase(&self) -> String
Returns the uppercase equivalent of this string slice, as a new String
.
‘Uppercase’ is defined according to the terms of the Unicode Derived Core Property
Uppercase
.
Since some characters can expand into multiple characters when changing
the case, this function returns a String
instead of modifying the
parameter in-place.
§Examples
Basic usage:
let s = "hello";
assert_eq!("HELLO", s.to_uppercase());
Scripts without case are not changed:
let new_year = "农历新年";
assert_eq!(new_year, new_year.to_uppercase());
One character can become multiple:
let s = "tschüß";
assert_eq!("TSCHÜSS", s.to_uppercase());
1.16.0 · sourcepub fn repeat(&self, n: usize) -> String
pub fn repeat(&self, n: usize) -> String
Creates a new String
by repeating a string n
times.
§Panics
This function will panic if the capacity would overflow.
§Examples
Basic usage:
assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
A panic upon overflow:
// this will panic at runtime
let huge = "0123456789abcdef".repeat(usize::MAX);
1.23.0 · sourcepub fn to_ascii_uppercase(&self) -> String
pub fn to_ascii_uppercase(&self) -> String
Returns a copy of this string where each character is mapped to its ASCII upper case equivalent.
ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.
To uppercase the value in-place, use make_ascii_uppercase
.
To uppercase ASCII characters in addition to non-ASCII characters, use
to_uppercase
.
§Examples
let s = "Grüße, Jürgen ❤";
assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
1.23.0 · sourcepub fn to_ascii_lowercase(&self) -> String
pub fn to_ascii_lowercase(&self) -> String
Returns a copy of this string where each character is mapped to its ASCII lower case equivalent.
ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.
To lowercase the value in-place, use make_ascii_lowercase
.
To lowercase ASCII characters in addition to non-ASCII characters, use
to_lowercase
.
§Examples
let s = "Grüße, Jürgen ❤";
assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
Trait Implementations§
1.0.0 · source§impl Add<&str> for String
impl Add<&str> for String
Implements the +
operator for concatenating two strings.
This consumes the String
on the left-hand side and re-uses its buffer (growing it if
necessary). This is done to avoid allocating a new String
and copying the entire contents on
every operation, which would lead to O(n^2) running time when building an n-byte string by
repeated concatenation.
The string on the right-hand side is only borrowed; its contents are copied into the returned
String
.
§Examples
Concatenating two String
s takes the first by value and borrows the second:
let a = String::from("hello");
let b = String::from(" world");
let c = a + &b;
// `a` is moved and can no longer be used here.
If you want to keep using the first String
, you can clone it and append to the clone instead:
let a = String::from("hello");
let b = String::from(" world");
let c = a.clone() + &b;
// `a` is still valid here.
Concatenating &str
slices can be done by converting the first to a String
:
let a = "hello";
let b = " world";
let c = a.to_string() + b;
1.12.0 · source§impl AddAssign<&str> for String
impl AddAssign<&str> for String
Implements the +=
operator for appending to a String
.
This has the same behavior as the push_str
method.
source§fn add_assign(&mut self, other: &str)
fn add_assign(&mut self, other: &str)
+=
operation. Read more§impl Arg for &String
impl Arg for &String
§fn to_string_lossy(&self) -> Cow<'_, str>
fn to_string_lossy(&self) -> Cow<'_, str>
Cow<'_, str>
.§fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
CStr
.§impl Arg for &String
impl Arg for &String
§fn to_string_lossy(&self) -> Cow<'_, str>
fn to_string_lossy(&self) -> Cow<'_, str>
Cow<'_, str>
.§fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
CStr
.§impl Arg for String
impl Arg for String
§fn to_string_lossy(&self) -> Cow<'_, str>
fn to_string_lossy(&self) -> Cow<'_, str>
Cow<'_, str>
.§fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
CStr
.§impl Arg for String
impl Arg for String
§fn to_string_lossy(&self) -> Cow<'_, str>
fn to_string_lossy(&self) -> Cow<'_, str>
Cow<'_, str>
.§fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
fn as_cow_c_str(&self) -> Result<Cow<'_, CStr>, Errno>
CStr
.source§impl Body for String
impl Body for String
§type Error = Infallible
type Error = Infallible
Body
might generate.source§fn poll_data(
self: Pin<&mut String>,
_cx: &mut Context<'_>,
) -> Poll<Option<Result<<String as Body>::Data, <String as Body>::Error>>>
fn poll_data( self: Pin<&mut String>, _cx: &mut Context<'_>, ) -> Poll<Option<Result<<String as Body>::Data, <String as Body>::Error>>>
source§fn poll_trailers(
self: Pin<&mut String>,
_cx: &mut Context<'_>,
) -> Poll<Result<Option<HeaderMap>, <String as Body>::Error>>
fn poll_trailers( self: Pin<&mut String>, _cx: &mut Context<'_>, ) -> Poll<Result<Option<HeaderMap>, <String as Body>::Error>>
HeaderMap
of trailers. Read moresource§fn is_end_stream(&self) -> bool
fn is_end_stream(&self) -> bool
true
when the end of stream has been reached. Read moresource§fn size_hint(&self) -> SizeHint
fn size_hint(&self) -> SizeHint
source§fn trailers(&mut self) -> Trailers<'_, Self>
fn trailers(&mut self) -> Trailers<'_, Self>
source§fn map_data<F, B>(self, f: F) -> MapData<Self, F>
fn map_data<F, B>(self, f: F) -> MapData<Self, F>
source§fn map_err<F, E>(self, f: F) -> MapErr<Self, F>
fn map_err<F, E>(self, f: F) -> MapErr<Self, F>
source§fn boxed_unsync(self) -> UnsyncBoxBody<Self::Data, Self::Error>
fn boxed_unsync(self) -> UnsyncBoxBody<Self::Data, Self::Error>
1.36.0 · source§impl BorrowMut<str> for String
impl BorrowMut<str> for String
source§fn borrow_mut(&mut self) -> &mut str
fn borrow_mut(&mut self) -> &mut str
source§impl DebugSecret for String
impl DebugSecret for String
§impl Decode for String
impl Decode for String
§fn decode<I>(input: &mut I) -> Result<String, Error>where
I: Input,
fn decode<I>(input: &mut I) -> Result<String, Error>where
I: Input,
§fn decode_into<I>(
input: &mut I,
dst: &mut MaybeUninit<Self>,
) -> Result<DecodeFinished, Error>where
I: Input,
fn decode_into<I>(
input: &mut I,
dst: &mut MaybeUninit<Self>,
) -> Result<DecodeFinished, Error>where
I: Input,
§fn skip<I>(input: &mut I) -> Result<(), Error>where
I: Input,
fn skip<I>(input: &mut I) -> Result<(), Error>where
I: Input,
§fn encoded_fixed_size() -> Option<usize>
fn encoded_fixed_size() -> Option<usize>
source§impl<'de> Deserialize<'de> for String
impl<'de> Deserialize<'de> for String
source§fn deserialize<D>(
deserializer: D,
) -> Result<String, <D as Deserializer<'de>>::Error>where
D: Deserializer<'de>,
fn deserialize<D>(
deserializer: D,
) -> Result<String, <D as Deserializer<'de>>::Error>where
D: Deserializer<'de>,
§impl EncodeAsType for String
impl EncodeAsType for String
§fn encode_as_type_to<R>(
&self,
type_id: <R as TypeResolver>::TypeId,
types: &R,
out: &mut Vec<u8>,
) -> Result<(), Error>where
R: TypeResolver,
fn encode_as_type_to<R>(
&self,
type_id: <R as TypeResolver>::TypeId,
types: &R,
out: &mut Vec<u8>,
) -> Result<(), Error>where
R: TypeResolver,
type_id
, types
, a context
and some output target for the SCALE encoded bytes,
attempt to SCALE encode the current value into the type given by type_id
.§impl EncodeTarget for String
impl EncodeTarget for String
§fn encode_with(
&mut self,
max_len: usize,
f: impl for<'a> FnOnce(&'a mut [u8]) -> Result<usize, Error>,
) -> Result<usize, Error>
fn encode_with( &mut self, max_len: usize, f: impl for<'a> FnOnce(&'a mut [u8]) -> Result<usize, Error>, ) -> Result<usize, Error>
1.2.0 · source§impl<'a> Extend<&'a char> for String
impl<'a> Extend<&'a char> for String
source§fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = &'a char>,
fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = &'a char>,
source§fn extend_one(&mut self, _: &'a char)
fn extend_one(&mut self, _: &'a char)
extend_one
)source§fn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)1.0.0 · source§impl<'a> Extend<&'a str> for String
impl<'a> Extend<&'a str> for String
source§fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = &'a str>,
fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = &'a str>,
source§fn extend_one(&mut self, s: &'a str)
fn extend_one(&mut self, s: &'a str)
extend_one
)source§fn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)1.45.0 · source§impl<A> Extend<Box<str, A>> for Stringwhere
A: Allocator,
impl<A> Extend<Box<str, A>> for Stringwhere
A: Allocator,
source§fn extend<I>(&mut self, iter: I)
fn extend<I>(&mut self, iter: I)
source§fn extend_one(&mut self, item: A)
fn extend_one(&mut self, item: A)
extend_one
)source§fn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)§impl<A> Extend<Box<str, A>> for Stringwhere
A: Allocator,
impl<A> Extend<Box<str, A>> for Stringwhere
A: Allocator,
§fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = Box<str, A>>,
fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = Box<str, A>>,
source§fn extend_one(&mut self, item: A)
fn extend_one(&mut self, item: A)
extend_one
)source§fn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)1.19.0 · source§impl<'a> Extend<Cow<'a, str>> for String
impl<'a> Extend<Cow<'a, str>> for String
source§fn extend<I>(&mut self, iter: I)
fn extend<I>(&mut self, iter: I)
source§fn extend_one(&mut self, s: Cow<'a, str>)
fn extend_one(&mut self, s: Cow<'a, str>)
extend_one
)source§fn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)1.4.0 · source§impl Extend<String> for String
impl Extend<String> for String
source§fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = String>,
fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = String>,
source§fn extend_one(&mut self, s: String)
fn extend_one(&mut self, s: String)
extend_one
)source§fn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)1.0.0 · source§impl Extend<char> for String
impl Extend<char> for String
source§fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = char>,
fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = char>,
source§fn extend_one(&mut self, c: char)
fn extend_one(&mut self, c: char)
extend_one
)source§fn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)1.14.0 · source§impl<'a> From<Cow<'a, str>> for String
impl<'a> From<Cow<'a, str>> for String
source§fn from(s: Cow<'a, str>) -> String
fn from(s: Cow<'a, str>) -> String
Converts a clone-on-write string to an owned
instance of String
.
This extracts the owned string, clones the string if it is not already owned.
§Example
// If the string is not owned...
let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
// It will allocate on the heap and copy the string.
let owned: String = String::from(cow);
assert_eq!(&owned[..], "eggplant");
§impl From<RuntimeString> for String
impl From<RuntimeString> for String
§fn from(string: RuntimeString) -> String
fn from(string: RuntimeString) -> String
§impl From<Ss58AddressFormat> for String
impl From<Ss58AddressFormat> for String
§fn from(x: Ss58AddressFormat) -> String
fn from(x: Ss58AddressFormat) -> String
1.6.0 · source§impl<'a> From<String> for Box<dyn Error + 'a>
impl<'a> From<String> for Box<dyn Error + 'a>
1.0.0 · source§impl<'a> From<String> for Box<dyn Error + Send + Sync + 'a>
impl<'a> From<String> for Box<dyn Error + Send + Sync + 'a>
source§fn from(err: String) -> Box<dyn Error + Send + Sync + 'a>
fn from(err: String) -> Box<dyn Error + Send + Sync + 'a>
Converts a String
into a box of dyn Error
+ Send
+ Sync
.
§Examples
use std::error::Error;
use std::mem;
let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
assert!(
mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
source§impl<'a> From<String> for LimitedStr<'a>
impl<'a> From<String> for LimitedStr<'a>
source§fn from(s: String) -> LimitedStr<'a>
fn from(s: String) -> LimitedStr<'a>
1.17.0 · source§impl<'a> FromIterator<&'a char> for String
impl<'a> FromIterator<&'a char> for String
1.0.0 · source§impl<'a> FromIterator<&'a str> for String
impl<'a> FromIterator<&'a str> for String
1.4.0 · source§impl FromIterator<String> for String
impl FromIterator<String> for String
1.0.0 · source§impl FromIterator<char> for String
impl FromIterator<char> for String
source§impl<'de, E> IntoDeserializer<'de, E> for Stringwhere
E: Error,
impl<'de, E> IntoDeserializer<'de, E> for Stringwhere
E: Error,
§type Deserializer = StringDeserializer<E>
type Deserializer = StringDeserializer<E>
source§fn into_deserializer(self) -> StringDeserializer<E>
fn into_deserializer(self) -> StringDeserializer<E>
§impl IntoVisitor for String
impl IntoVisitor for String
§type AnyVisitor<R: TypeResolver> = BasicVisitor<String, R>
type AnyVisitor<R: TypeResolver> = BasicVisitor<String, R>
Self
.§fn into_visitor<R>() -> <String as IntoVisitor>::AnyVisitor<R>where
R: TypeResolver,
fn into_visitor<R>() -> <String as IntoVisitor>::AnyVisitor<R>where
R: TypeResolver,
1.0.0 · source§impl Ord for String
impl Ord for String
source§impl PartialEq<HeaderValue> for String
impl PartialEq<HeaderValue> for String
source§impl PartialEq<PathAndQuery> for String
impl PartialEq<PathAndQuery> for String
source§impl PartialEq<String> for HeaderValue
impl PartialEq<String> for HeaderValue
source§impl PartialEq<String> for PathAndQuery
impl PartialEq<String> for PathAndQuery
§impl<'a, 'b> PartialOrd<&'a BStr> for String
impl<'a, 'b> PartialOrd<&'a BStr> for String
source§impl PartialOrd<Authority> for String
impl PartialOrd<Authority> for String
§impl<'a, 'b> PartialOrd<BStr> for String
impl<'a, 'b> PartialOrd<BStr> for String
§impl<'a, 'b> PartialOrd<BString> for String
impl<'a, 'b> PartialOrd<BString> for String
§impl PartialOrd<Bytes> for String
impl PartialOrd<Bytes> for String
§impl PartialOrd<BytesMut> for String
impl PartialOrd<BytesMut> for String
source§impl PartialOrd<HeaderValue> for String
impl PartialOrd<HeaderValue> for String
source§impl PartialOrd<PathAndQuery> for String
impl PartialOrd<PathAndQuery> for String
§impl<'a, 'b> PartialOrd<String> for &'a BStr
impl<'a, 'b> PartialOrd<String> for &'a BStr
source§impl PartialOrd<String> for Authority
impl PartialOrd<String> for Authority
§impl<'a, 'b> PartialOrd<String> for BStr
impl<'a, 'b> PartialOrd<String> for BStr
§impl<'a, 'b> PartialOrd<String> for BString
impl<'a, 'b> PartialOrd<String> for BString
§impl PartialOrd<String> for Bytes
impl PartialOrd<String> for Bytes
§impl PartialOrd<String> for BytesMut
impl PartialOrd<String> for BytesMut
source§impl PartialOrd<String> for HeaderValue
impl PartialOrd<String> for HeaderValue
source§impl PartialOrd<String> for PathAndQuery
impl PartialOrd<String> for PathAndQuery
1.0.0 · source§impl PartialOrd for String
impl PartialOrd for String
source§impl<'b> Pattern for &'b String
impl<'b> Pattern for &'b String
A convenience impl that delegates to the impl for &str
.
§Examples
assert_eq!(String::from("Hello world").find("world"), Some(6));
§type Searcher<'a> = <&'b str as Pattern>::Searcher<'a>
type Searcher<'a> = <&'b str as Pattern>::Searcher<'a>
pattern
)source§fn into_searcher(self, haystack: &str) -> <&'b str as Pattern>::Searcher<'_>
fn into_searcher(self, haystack: &str) -> <&'b str as Pattern>::Searcher<'_>
pattern
)self
and the haystack
to search in.source§fn is_contained_in(self, haystack: &str) -> bool
fn is_contained_in(self, haystack: &str) -> bool
pattern
)source§fn is_prefix_of(self, haystack: &str) -> bool
fn is_prefix_of(self, haystack: &str) -> bool
pattern
)source§fn strip_prefix_of(self, haystack: &str) -> Option<&str>
fn strip_prefix_of(self, haystack: &str) -> Option<&str>
pattern
)source§fn is_suffix_of<'a>(self, haystack: &'a str) -> bool
fn is_suffix_of<'a>(self, haystack: &'a str) -> bool
pattern
)§impl<'a> Replacer for &'a String
impl<'a> Replacer for &'a String
§fn replace_append(&mut self, caps: &Captures<'_>, dst: &mut String)
fn replace_append(&mut self, caps: &Captures<'_>, dst: &mut String)
dst
to replace the current match. Read more§impl Replacer for String
impl Replacer for String
§fn replace_append(&mut self, caps: &Captures<'_>, dst: &mut String)
fn replace_append(&mut self, caps: &Captures<'_>, dst: &mut String)
dst
to replace the current match. Read moresource§impl Serialize for String
impl Serialize for String
source§fn serialize<S>(
&self,
serializer: S,
) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error>where
S: Serializer,
fn serialize<S>(
&self,
serializer: S,
) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error>where
S: Serializer,
1.16.0 · source§impl ToSocketAddrs for String
impl ToSocketAddrs for String
§type Iter = IntoIter<SocketAddr>
type Iter = IntoIter<SocketAddr>
source§fn to_socket_addrs(&self) -> Result<IntoIter<SocketAddr>, Error>
fn to_socket_addrs(&self) -> Result<IntoIter<SocketAddr>, Error>
SocketAddr
s. Read moresource§impl<'a> TryFrom<&'a String> for HeaderName
impl<'a> TryFrom<&'a String> for HeaderName
§type Error = InvalidHeaderName
type Error = InvalidHeaderName
source§fn try_from(
s: &'a String,
) -> Result<HeaderName, <HeaderName as TryFrom<&'a String>>::Error>
fn try_from( s: &'a String, ) -> Result<HeaderName, <HeaderName as TryFrom<&'a String>>::Error>
source§impl<'a> TryFrom<&'a String> for HeaderValue
impl<'a> TryFrom<&'a String> for HeaderValue
§type Error = InvalidHeaderValue
type Error = InvalidHeaderValue
source§fn try_from(
s: &'a String,
) -> Result<HeaderValue, <HeaderValue as TryFrom<&'a String>>::Error>
fn try_from( s: &'a String, ) -> Result<HeaderValue, <HeaderValue as TryFrom<&'a String>>::Error>
source§impl TryFrom<&String> for PathAndQuery
impl TryFrom<&String> for PathAndQuery
§type Error = InvalidUri
type Error = InvalidUri
source§fn try_from(
s: &String,
) -> Result<PathAndQuery, <PathAndQuery as TryFrom<&String>>::Error>
fn try_from( s: &String, ) -> Result<PathAndQuery, <PathAndQuery as TryFrom<&String>>::Error>
source§impl TryFrom<String> for HeaderName
impl TryFrom<String> for HeaderName
§type Error = InvalidHeaderName
type Error = InvalidHeaderName
source§fn try_from(
s: String,
) -> Result<HeaderName, <HeaderName as TryFrom<String>>::Error>
fn try_from( s: String, ) -> Result<HeaderName, <HeaderName as TryFrom<String>>::Error>
source§impl TryFrom<String> for HeaderValue
impl TryFrom<String> for HeaderValue
§type Error = InvalidHeaderValue
type Error = InvalidHeaderValue
source§fn try_from(
t: String,
) -> Result<HeaderValue, <HeaderValue as TryFrom<String>>::Error>
fn try_from( t: String, ) -> Result<HeaderValue, <HeaderValue as TryFrom<String>>::Error>
source§impl TryFrom<String> for PathAndQuery
impl TryFrom<String> for PathAndQuery
§type Error = InvalidUri
type Error = InvalidUri
source§fn try_from(
s: String,
) -> Result<PathAndQuery, <PathAndQuery as TryFrom<String>>::Error>
fn try_from( s: String, ) -> Result<PathAndQuery, <PathAndQuery as TryFrom<String>>::Error>
source§impl WasmEntryPoint for String
impl WasmEntryPoint for String
source§fn try_from_entry(entry: &str) -> Option<String>
fn try_from_entry(entry: &str) -> Option<String>
source§fn try_into_kind(&self) -> Option<DispatchKind>
fn try_into_kind(&self) -> Option<DispatchKind>
DispatchKind
.1.0.0 · source§impl Write for String
impl Write for String
source§impl<'a> WriteFormatted for &'a mut String
impl<'a> WriteFormatted for &'a mut String
source§fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> Result<usize, Error>where
F: Format,
N: ToFormattedString,
fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> Result<usize, Error>where
F: Format,
N: ToFormattedString,
io::Write
’s write_all
method or
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’s write_str
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impl WriteFormatted for String
source§fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> Result<usize, Error>where
F: Format,
N: ToFormattedString,
fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> Result<usize, Error>where
F: Format,
N: ToFormattedString,
io::Write
’s write_all
method or
fmt::Write
’s write_str
method. On success, returns the number of bytes written. Read moreimpl<'a> AsHeaderName for &'a String
impl AsHeaderName for String
impl CloneableSecret for String
impl DerefPure for String
impl EncodeLike<&str> for String
impl EncodeLike<String> for &str
impl EncodeLike for String
impl Eq for String
impl<T> FromStream<T> for String
impl Index for String
impl StableDeref for String
impl StructuralPartialEq for String
impl ToSocketAddrs for String
impl WrapperTypeEncode for String
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impl Freeze for String
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impl Send for String
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§impl<A, T> AsBits<T> for A
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§impl<T, U> AsByteSlice<T> for U
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fn as_byte_slice(&self) -> &[u8] ⓘ
§impl<U> AsSliceOf for U
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