Enum gstd::prelude::Option

1.0.0 · source ·

pub enum Option<T> {
    None,
    Some(T),
}

Expand description

The Option type. See the module level documentation for more.

Variants§

§1.0.0

None

No value.

§1.0.0

Some(T)

Some value of type T.

Implementations§

source §

let x: Option<u32> = Some(2);
assert_eq!(x.is_none(), false);

let x: Option<u32> = None;
assert_eq!(x.is_none(), true);

source

pub fn is_none_or(self, f: impl FnOnce(T) -> bool) -> bool

🔬This is a nightly-only experimental API. (is_none_or)

Returns true if the option is a None or the value inside of it matches a predicate.

§Examples

#![feature(is_none_or)]

let x: Option<u32> = Some(2);
assert_eq!(x.is_none_or(|x| x > 1), true);

let x: Option<u32> = Some(0);
assert_eq!(x.is_none_or(|x| x > 1), false);

let x: Option<u32> = None;
assert_eq!(x.is_none_or(|x| x > 1), true);

1.0.0 (const: 1.48.0) · source

pub const fn as_ref(&self) -> Option<&T>

Converts from &Option<T> to Option<&T>.

§Examples

Calculates the length of an Option<String> as an Option<usize> without moving the String. The map method takes the self argument by value, consuming the original, so this technique uses as_ref to first take an Option to a reference to the value inside the original.

let text: Option<String> = Some("Hello, world!".to_string());
// First, cast `Option<String>` to `Option<&String>` with `as_ref`,
// then consume *that* with `map`, leaving `text` on the stack.
let text_length: Option<usize> = text.as_ref().map(|s| s.len());
println!("still can print text: {text:?}");

1.0.0 (const: unstable) · source

pub fn as_mut(&mut self) -> Option<&mut T>

Converts from &mut Option<T> to Option<&mut T>.

§Examples

let mut x = Some(2);
match x.as_mut() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));

1.33.0 (const: unstable) · source

pub fn as_pin_ref(self: Pin<&Option<T>>) -> Option<Pin<&T>>

Converts from Pin<&Option<T>> to Option<Pin<&T>>.

1.33.0 (const: unstable) · source

pub fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&mut T>>

Converts from Pin<&mut Option<T>> to Option<Pin<&mut T>>.

1.75.0 (const: unstable) · source

pub fn as_slice(&self) -> &[T]

Returns a slice of the contained value, if any. If this is None, an empty slice is returned. This can be useful to have a single type of iterator over an Option or slice.

Note: Should you have an Option<&T> and wish to get a slice of T, you can unpack it via opt.map_or(&[], std::slice::from_ref).

§Examples

assert_eq!(
    [Some(1234).as_slice(), None.as_slice()],
    [&[1234][..], &[][..]],
);

The inverse of this function is (discounting borrowing) [_]::first:

for i in [Some(1234_u16), None] {
    assert_eq!(i.as_ref(), i.as_slice().first());
}

1.75.0 (const: unstable) · source

pub fn as_mut_slice(&mut self) -> &mut [T]

Returns a mutable slice of the contained value, if any. If this is None, an empty slice is returned. This can be useful to have a single type of iterator over an Option or slice.

Note: Should you have an Option<&mut T> instead of a &mut Option<T>, which this method takes, you can obtain a mutable slice via opt.map_or(&mut [], std::slice::from_mut).

§Examples

assert_eq!(
    [Some(1234).as_mut_slice(), None.as_mut_slice()],
    [&mut [1234][..], &mut [][..]],
);

The result is a mutable slice of zero or one items that points into our original Option:

let mut x = Some(1234);
x.as_mut_slice()[0] += 1;
assert_eq!(x, Some(1235));

The inverse of this method (discounting borrowing) is [_]::first_mut:

assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123))

1.0.0 (const: unstable) · source

pub fn expect(self, msg: &str) -> T

Returns the contained Some value, consuming the self value.

§Panics

Panics if the value is a None with a custom panic message provided by msg.

§Examples

let x = Some("value");
assert_eq!(x.expect("fruits are healthy"), "value");

let x: Option<&str> = None;
x.expect("fruits are healthy"); // panics with `fruits are healthy`

§Recommended Message Style

We recommend that expect messages are used to describe the reason you expect the Option should be Some.

let item = slice.get(0)
    .expect("slice should not be empty");

Hint: If you’re having trouble remembering how to phrase expect error messages remember to focus on the word “should” as in “env variable should be set by blah” or “the given binary should be available and executable by the current user”.

For more detail on expect message styles and the reasoning behind our recommendation please refer to the section on “Common Message Styles” in the std::error module docs.

1.0.0 (const: unstable) · source

pub fn unwrap(self) -> T

Returns the contained Some value, consuming the self value.

Because this function may panic, its use is generally discouraged. Instead, prefer to use pattern matching and handle the None case explicitly, or call unwrap_or, unwrap_or_else, or unwrap_or_default.

§Panics

Panics if the self value equals None.

§Examples

let x = Some("air");
assert_eq!(x.unwrap(), "air");

let x: Option<&str> = None;
assert_eq!(x.unwrap(), "air"); // fails

1.0.0 · source

pub fn unwrap_or(self, default: T) -> T

Returns the contained Some value or a provided default.

Arguments passed to unwrap_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use unwrap_or_else, which is lazily evaluated.

§Examples

assert_eq!(Some("car").unwrap_or("bike"), "car");
assert_eq!(None.unwrap_or("bike"), "bike");

1.0.0 · source

pub fn unwrap_or_else<F>(self, f: F) -> T
where F: FnOnce() -> T,

Returns the contained Some value or computes it from a closure.

§Examples

let k = 10;
assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4);
assert_eq!(None.unwrap_or_else(|| 2 * k), 20);

1.0.0 · source

pub fn unwrap_or_default(self) -> T
where T: Default,

Returns the contained Some value or a default.

Consumes the self argument then, if Some, returns the contained value, otherwise if None, returns the default value for that type.

§Examples

let x: Option<u32> = None;
let y: Option<u32> = Some(12);

assert_eq!(x.unwrap_or_default(), 0);
assert_eq!(y.unwrap_or_default(), 12);

1.58.0 (const: unstable) · source

pub unsafe fn unwrap_unchecked(self) -> T

Returns the contained Some value, consuming the self value, without checking that the value is not None.

§Safety

Calling this method on None is undefined behavior.

§Examples

let x = Some("air");
assert_eq!(unsafe { x.unwrap_unchecked() }, "air");

let x: Option<&str> = None;
assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior!

1.0.0 · source

pub fn map<U, F>(self, f: F) -> Option
where F: FnOnce(T) -> U,

Maps an Option<T> to Option by applying a function to a contained value (if Some) or returns None (if None).

§Examples

Calculates the length of an Option<String> as an Option<usize>, consuming the original:

let maybe_some_string = Some(String::from("Hello, World!"));
// `Option::map` takes self *by value*, consuming `maybe_some_string`
let maybe_some_len = maybe_some_string.map(|s| s.len());
assert_eq!(maybe_some_len, Some(13));

let x: Option<&str> = None;
assert_eq!(x.map(|s| s.len()), None);

1.76.0 · source

pub fn inspect<F>(self, f: F) -> Option<T>
where F: FnOnce(&T),

Calls a function with a reference to the contained value if Some.

Returns the original option.

§Examples

let list = vec![1, 2, 3];

// prints "got: 2"
let x = list
    .get(1)
    .inspect(|x| println!("got: {x}"))
    .expect("list should be long enough");

// prints nothing
list.get(5).inspect(|x| println!("got: {x}"));

1.0.0 · source

pub fn map_or<U, F>(self, default: U, f: F) -> U
where F: FnOnce(T) -> U,

Returns the provided default result (if none), or applies a function to the contained value (if any).

Arguments passed to map_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use map_or_else, which is lazily evaluated.

§Examples

let x = Some("foo");
assert_eq!(x.map_or(42, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or(42, |v| v.len()), 42);

1.0.0 · source

pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U
where D: FnOnce() -> U, F: FnOnce(T) -> U,

Computes a default function result (if none), or applies a different function to the contained value (if any).

§Basic examples

let k = 21;

let x = Some("foo");
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42);

§Handling a Result-based fallback

A somewhat common occurrence when dealing with optional values in combination with Result<T, E> is the case where one wants to invoke a fallible fallback if the option is not present. This example parses a command line argument (if present), or the contents of a file to an integer. However, unlike accessing the command line argument, reading the file is fallible, so it must be wrapped with Ok.

let v: u64 = std::env::args()
   .nth(1)
   .map_or_else(|| std::fs::read_to_string("/etc/someconfig.conf"), Ok)?
   .parse()?;

1.0.0 · source

pub fn ok_or<E>(self, err: E) -> Result<T, E>

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err).

Arguments passed to ok_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use ok_or_else, which is lazily evaluated.

§Examples

let x = Some("foo");
assert_eq!(x.ok_or(0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or(0), Err(0));

1.0.0 · source

pub fn ok_or_else<E, F>(self, err: F) -> Result<T, E>
where F: FnOnce() -> E,

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err()).

§Examples

let x = Some("foo");
assert_eq!(x.ok_or_else(|| 0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or_else(|| 0), Err(0));

1.40.0 · source

pub fn as_deref(&self) -> Option<&<T as Deref>::Target>
where T: Deref,

Converts from Option<T> (or &Option<T>) to Option<&T::Target>.

Leaves the original Option in-place, creating a new one with a reference to the original one, additionally coercing the contents via Deref.

§Examples

let x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref(), Some("hey"));

let x: Option<String> = None;
assert_eq!(x.as_deref(), None);

1.40.0 · source

pub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::Target>
where T: DerefMut,

Converts from Option<T> (or &mut Option<T>) to Option<&mut T::Target>.

Leaves the original Option in-place, creating a new one containing a mutable reference to the inner type’s Deref::Target type.

§Examples

let mut x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref_mut().map(|x| {
    x.make_ascii_uppercase();
    x
}), Some("HEY".to_owned().as_mut_str()));

1.0.0 (const: unstable) · source

pub fn iter(&self) -> Iter<'_, T> ⓘ

Returns an iterator over the possibly contained value.

§Examples

let x = Some(4);
assert_eq!(x.iter().next(), Some(&4));

let x: Option<u32> = None;
assert_eq!(x.iter().next(), None);

1.0.0 · source

pub fn iter_mut(&mut self) -> IterMut<'_, T> ⓘ

Returns a mutable iterator over the possibly contained value.

§Examples

let mut x = Some(4);
match x.iter_mut().next() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));

let mut x: Option<u32> = None;
assert_eq!(x.iter_mut().next(), None);

1.0.0 · source

pub fn and(self, optb: Option) -> Option

Returns None if the option is None, otherwise returns optb.

Arguments passed to and are eagerly evaluated; if you are passing the result of a function call, it is recommended to use and_then, which is lazily evaluated.

§Examples

let x = Some(2);
let y: Option<&str> = None;
assert_eq!(x.and(y), None);

let x: Option<u32> = None;
let y = Some("foo");
assert_eq!(x.and(y), None);

let x = Some(2);
let y = Some("foo");
assert_eq!(x.and(y), Some("foo"));

let x: Option<u32> = None;
let y: Option<&str> = None;
assert_eq!(x.and(y), None);

1.0.0 · source

pub fn and_then<U, F>(self, f: F) -> Option
where F: FnOnce(T) -> Option,

Returns None if the option is None, otherwise calls f with the wrapped value and returns the result.

Some languages call this operation flatmap.

§Examples

fn sq_then_to_string(x: u32) -> Option<String> {
    x.checked_mul(x).map(|sq| sq.to_string())
}

assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string()));
assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None); // overflowed!
assert_eq!(None.and_then(sq_then_to_string), None);

Often used to chain fallible operations that may return None.

let arr_2d = [["A0", "A1"], ["B0", "B1"]];

let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1));
assert_eq!(item_0_1, Some(&"A1"));

let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0));
assert_eq!(item_2_0, None);

1.27.0 · source

pub fn filter(self, predicate: P) -> Option<T>
where P: FnOnce(&T) -> bool,

Returns None if the option is None, otherwise calls predicate with the wrapped value and returns:

Some(t) if predicate returns true (where t is the wrapped value), and
None if predicate returns false.

This function works similar to Iterator::filter(). You can imagine the Option<T> being an iterator over one or zero elements. filter() lets you decide which elements to keep.

§Examples

fn is_even(n: &i32) -> bool {
    n % 2 == 0
}

assert_eq!(None.filter(is_even), None);
assert_eq!(Some(3).filter(is_even), None);
assert_eq!(Some(4).filter(is_even), Some(4));

1.0.0 · source

pub fn or(self, optb: Option<T>) -> Option<T>

Returns the option if it contains a value, otherwise returns optb.

Arguments passed to or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use or_else, which is lazily evaluated.

§Examples

let x = Some(2);
let y = None;
assert_eq!(x.or(y), Some(2));

let x = None;
let y = Some(100);
assert_eq!(x.or(y), Some(100));

let x = Some(2);
let y = Some(100);
assert_eq!(x.or(y), Some(2));

let x: Option<u32> = None;
let y = None;
assert_eq!(x.or(y), None);

1.0.0 · source

pub fn or_else<F>(self, f: F) -> Option<T>
where F: FnOnce() -> Option<T>,

Returns the option if it contains a value, otherwise calls f and returns the result.

§Examples

fn nobody() -> Option<&'static str> { None }
fn vikings() -> Option<&'static str> { Some("vikings") }

assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians"));
assert_eq!(None.or_else(vikings), Some("vikings"));
assert_eq!(None.or_else(nobody), None);

1.37.0 · source

pub fn xor(self, optb: Option<T>) -> Option<T>

Returns Some if exactly one of self, optb is Some, otherwise returns None.

§Examples

let x = Some(2);
let y: Option<u32> = None;
assert_eq!(x.xor(y), Some(2));

let x: Option<u32> = None;
let y = Some(2);
assert_eq!(x.xor(y), Some(2));

let x = Some(2);
let y = Some(2);
assert_eq!(x.xor(y), None);

let x: Option<u32> = None;
let y: Option<u32> = None;
assert_eq!(x.xor(y), None);

1.53.0 · source

pub fn insert(&mut self, value: T) -> &mut T

Inserts value into the option, then returns a mutable reference to it.

If the option already contains a value, the old value is dropped.

See also Option::get_or_insert, which doesn’t update the value if the option already contains Some.

§Example

let mut opt = None;
let val = opt.insert(1);
assert_eq!(*val, 1);
assert_eq!(opt.unwrap(), 1);
let val = opt.insert(2);
assert_eq!(*val, 2);
*val = 3;
assert_eq!(opt.unwrap(), 3);

1.20.0 · source

pub fn get_or_insert(&mut self, value: T) -> &mut T

Inserts value into the option if it is None, then returns a mutable reference to the contained value.

See also Option::insert, which updates the value even if the option already contains Some.

§Examples

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert(5);
    assert_eq!(y, &5);

    *y = 7;
}

assert_eq!(x, Some(7));

source

pub fn get_or_insert_default(&mut self) -> &mut T
where T: Default,

🔬This is a nightly-only experimental API. (option_get_or_insert_default)

Inserts the default value into the option if it is None, then returns a mutable reference to the contained value.

§Examples

#![feature(option_get_or_insert_default)]

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_default();
    assert_eq!(y, &0);

    *y = 7;
}

assert_eq!(x, Some(7));

1.20.0 · source

pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T
where F: FnOnce() -> T,

Inserts a value computed from f into the option if it is None, then returns a mutable reference to the contained value.

§Examples

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_with(|| 5);
    assert_eq!(y, &5);

    *y = 7;
}

assert_eq!(x, Some(7));

1.0.0 (const: unstable) · source

pub fn take(&mut self) -> Option<T>

Takes the value out of the option, leaving a None in its place.

§Examples

let mut x = Some(2);
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, Some(2));

let mut x: Option<u32> = None;
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, None);

1.80.0 · source

pub fn take_if(&mut self, predicate: P) -> Option<T>
where P: FnOnce(&mut T) -> bool,

Takes the value out of the option, but only if the predicate evaluates to true on a mutable reference to the value.

In other words, replaces self with None if the predicate returns true. This method operates similar to Option::take but conditional.

§Examples

let mut x = Some(42);

let prev = x.take_if(|v| if *v == 42 {
    *v += 1;
    false
} else {
    false
});
assert_eq!(x, Some(43));
assert_eq!(prev, None);

let prev = x.take_if(|v| *v == 43);
assert_eq!(x, None);
assert_eq!(prev, Some(43));

1.31.0 (const: unstable) · source

pub fn replace(&mut self, value: T) -> Option<T>

Replaces the actual value in the option by the value given in parameter, returning the old value if present, leaving a Some in its place without deinitializing either one.

§Examples

let mut x = Some(2);
let old = x.replace(5);
assert_eq!(x, Some(5));
assert_eq!(old, Some(2));

let mut x = None;
let old = x.replace(3);
assert_eq!(x, Some(3));
assert_eq!(old, None);

1.46.0 · source

pub fn zip(self, other: Option) -> Option<(T, U)>

Zips self with another Option.

If self is Some(s) and other is Some(o), this method returns Some((s, o)). Otherwise, None is returned.

§Examples

let x = Some(1);
let y = Some("hi");
let z = None::<u8>;

assert_eq!(x.zip(y), Some((1, "hi")));
assert_eq!(x.zip(z), None);

source

pub fn zip_with<U, F, R>(self, other: Option, f: F) -> Option<R>
where F: FnOnce(T, U) -> R,

🔬This is a nightly-only experimental API. (option_zip)

Zips self and another Option with function f.

If self is Some(s) and other is Some(o), this method returns Some(f(s, o)). Otherwise, None is returned.

§Examples

#![feature(option_zip)]

#[derive(Debug, PartialEq)]
struct Point {
    x: f64,
    y: f64,
}

impl Point {
    fn new(x: f64, y: f64) -> Self {
        Self { x, y }
    }
}

let x = Some(17.5);
let y = Some(42.7);

assert_eq!(x.zip_with(y, Point::new), Some(Point { x: 17.5, y: 42.7 }));
assert_eq!(x.zip_with(None, Point::new), None);

source §

impl<T, U> Option<(T, U)>

1.66.0 · source

pub fn unzip(self) -> (Option<T>, Option)

Unzips an option containing a tuple of two options.

If self is Some((a, b)) this method returns (Some(a), Some(b)). Otherwise, (None, None) is returned.

§Examples

let x = Some((1, "hi"));
let y = None::<(u8, u32)>;

assert_eq!(x.unzip(), (Some(1), Some("hi")));
assert_eq!(y.unzip(), (None, None));

source §

impl<T> Option<&T>

1.35.0 (const: unstable) · source

pub fn copied(self) -> Option<T>
where T: Copy,

Maps an Option<&T> to an Option<T> by copying the contents of the option.

§Examples

let x = 12;
let opt_x = Some(&x);
assert_eq!(opt_x, Some(&12));
let copied = opt_x.copied();
assert_eq!(copied, Some(12));

1.0.0 · source

pub fn cloned(self) -> Option<T>
where T: Clone,

Maps an Option<&T> to an Option<T> by cloning the contents of the option.

§Examples

let x = 12;
let opt_x = Some(&x);
assert_eq!(opt_x, Some(&12));
let cloned = opt_x.cloned();
assert_eq!(cloned, Some(12));

source §

impl<T> Option<&mut T>

1.35.0 (const: unstable) · source

pub fn copied(self) -> Option<T>
where T: Copy,

Maps an Option<&mut T> to an Option<T> by copying the contents of the option.

§Examples

let mut x = 12;
let opt_x = Some(&mut x);
assert_eq!(opt_x, Some(&mut 12));
let copied = opt_x.copied();
assert_eq!(copied, Some(12));

1.26.0 · source

pub fn cloned(self) -> Option<T>
where T: Clone,

Maps an Option<&mut T> to an Option<T> by cloning the contents of the option.

§Examples

let mut x = 12;
let opt_x = Some(&mut x);
assert_eq!(opt_x, Some(&mut 12));
let cloned = opt_x.cloned();
assert_eq!(cloned, Some(12));

source §

impl<T, E> Option<Result<T, E>>

1.33.0 (const: unstable) · source

pub fn transpose(self) -> Result<Option<T>, E>

Transposes an Option of a Result into a Result of an Option.

None will be mapped to Ok(None). Some(Ok(_)) and Some(Err(_)) will be mapped to Ok(Some(_)) and Err(_).

§Examples

#[derive(Debug, Eq, PartialEq)]
struct SomeErr;

let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
assert_eq!(x, y.transpose());

source §

impl<T> Option<Option<T>>

1.40.0 (const: unstable) · source

pub fn flatten(self) -> Option<T>

Converts from Option<Option<T>> to Option<T>.

§Examples

Basic usage:

let x: Option<Option<u32>> = Some(Some(6));
assert_eq!(Some(6), x.flatten());

let x: Option<Option<u32>> = Some(None);
assert_eq!(None, x.flatten());

let x: Option<Option<u32>> = None;
assert_eq!(None, x.flatten());

Flattening only removes one level of nesting at a time:

let x: Option<Option<Option<u32>>> = Some(Some(Some(6)));
assert_eq!(Some(Some(6)), x.flatten());
assert_eq!(Some(6), x.flatten().flatten());

Trait Implementations§

§

Gets the bytes of this value. Read more

§

fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,

Gets the bytes of this value mutably. Read more

§

fn write_to(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to bytes. Read more

§

fn write_to_prefix(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to the prefix of bytes. Read more

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fn write_to_suffix(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to the suffix of bytes. Read more

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Gets the bytes of this value. Read more

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fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,

Gets the bytes of this value mutably. Read more

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fn write_to(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to bytes. Read more

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fn write_to_prefix(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to the prefix of bytes. Read more

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fn write_to_suffix(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to the suffix of bytes. Read more

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Gets the bytes of this value. Read more

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fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,

Gets the bytes of this value mutably. Read more

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fn write_to(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to bytes. Read more

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fn write_to_prefix(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to the prefix of bytes. Read more

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fn write_to_suffix(&self, bytes: &mut [u8]) -> Option<()>

Writes a copy of self to the suffix of bytes. Read more

1.0.0 · source§

impl<T> Clone for Option<T>
where T: Clone,

source §

fn clone(&self) -> Option<T>

Returns a copy of the value. Read more

Attempt to deserialize the value from input into a pre-allocated piece of memory. Read more

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fn skip(input: &mut I) -> Result<(), Error>
where I: Input,

Attempt to skip the encoded value from input. Read more

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fn encoded_fixed_size() -> Option<usize>

Returns the fixed encoded size of the type. Read more

1.0.0 · source§

impl<T> Default for Option<T>

source §

fn default() -> Option<T>

Returns None.

§Examples

let opt: Option<u32> = Option::default();
assert!(opt.is_none());

§

source §

fn from(o: &'a Option<T>) -> Option<&'a T>

Converts from &Option<T> to Option<&T>.

§Examples

Converts an Option<String> into an Option<usize>, preserving the original. The map method takes the self argument by value, consuming the original, so this technique uses from to first take an Option to a reference to the value inside the original.

let s: Option<String> = Some(String::from("Hello, Rustaceans!"));
let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len());

println!("Can still print s: {s:?}");

assert_eq!(o, Some(18));

1.30.0 · source§

impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>

source §

fn from(o: &'a mut Option<T>) -> Option<&'a mut T>

Converts from &mut Option<T> to Option<&mut T>

§Examples

let mut s = Some(String::from("Hello"));
let o: Option<&mut String> = Option::from(&mut s);

match o {
    Some(t) => *t = String::from("Hello, Rustaceans!"),
    None => (),
}

assert_eq!(s, Some(String::from("Hello, Rustaceans!")));

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impl<T> From<CtOption<T>> for Option<T>

source §

fn from(source: CtOption<T>) -> Option<T>

Convert the CtOption<T> wrapper into an Option<T>, depending on whether the underlying is_some Choice was a 0 or a 1 once unwrapped.

§Note

This function exists to avoid ending up with ugly, verbose and/or bad handled conversions from the CtOption<T> wraps to an Option<T> or Result<T, E>. This implementation doesn’t intend to be constant-time nor try to protect the leakage of the T since the Option<T> will do it anyways.

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impl<T> From<Option<T>> for OptionFuture<T>

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fn from(option: Option<T>) -> OptionFuture<T> ⓘ

Converts to this type from the input type.

1.12.0 · source§

impl<T> From<T> for Option<T>

source §

fn from(val: T) -> Option<T>

Moves val into a new Some.

§Examples

let o: Option<u8> = Option::from(67);

assert_eq!(Some(67), o);

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Reads a copy of Self from the suffix of bytes. Read more

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Reads a copy of Self from the suffix of bytes. Read more

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Reads a copy of Self from the suffix of bytes. Read more

1.0.0 · source§

impl<A, V> FromIterator<Option<A>> for Option<V>
where V: FromIterator<A>,

source §

fn from_iter(iter: I) -> Option<V>
where I: IntoIterator<Item = Option<A>>,

Takes each element in the Iterator: if it is None, no further elements are taken, and the None is returned. Should no None occur, a container of type V containing the values of each Option is returned.

§Examples

Here is an example which increments every integer in a vector. We use the checked variant of add that returns None when the calculation would result in an overflow.

let items = vec![0_u16, 1, 2];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_add(1))
    .collect();

assert_eq!(res, Some(vec![1, 2, 3]));

As you can see, this will return the expected, valid items.

Here is another example that tries to subtract one from another list of integers, this time checking for underflow:

let items = vec![2_u16, 1, 0];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_sub(1))
    .collect();

assert_eq!(res, None);

Since the last element is zero, it would underflow. Thus, the resulting value is None.

Here is a variation on the previous example, showing that no further elements are taken from iter after the first None.

let items = vec![3_u16, 2, 1, 10];

let mut shared = 0;

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| { shared += x; x.checked_sub(2) })
    .collect();

assert_eq!(res, None);
assert_eq!(shared, 6);

Since the third element caused an underflow, no further elements were taken, so the final value of shared is 6 (= 3 + 2 + 1), not 16.

impl<'a, T> IntoIterator for &'a mut Option<T>

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type Item = &'a mut T

The type of the elements being iterated over.

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type IntoIter = IterMut<'a, T>

Which kind of iterator are we turning this into?

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fn into_iter(self) -> IterMut<'a, T> ⓘ

Creates an iterator from a value. Read more

1.0.0 · source§

impl<T> IntoIterator for Option<T>

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fn into_iter(self) -> IntoIter<T> ⓘ

Returns a consuming iterator over the possibly contained value.

§Examples

let x = Some("string");
let v: Vec<&str> = x.into_iter().collect();
assert_eq!(v, ["string"]);

let x = None;
let v: Vec<&str> = x.into_iter().collect();
assert!(v.is_empty());

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type Item = T

The type of the elements being iterated over.

Compares and returns the maximum of two values. Read more

1.21.0 · source§

fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more

1.50.0 · source§

fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more

1.0.0 · source§

impl<T> PartialEq for Option<T>
where T: PartialEq,

source §

fn eq(&self, other: &Option<T>) -> bool

Tests for self and other values to be equal, and is used by ==.

1.0.0 · source§

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

1.0.0 · source§

source §

fn product(iter: I) -> Option<T>
where I: Iterator<Item = Option>,

Takes each element in the Iterator: if it is a None, no further elements are taken, and the None is returned. Should no None occur, the product of all elements is returned.

§Examples

This multiplies each number in a vector of strings, if a string could not be parsed the operation returns None:

let nums = vec!["5", "10", "1", "2"];
let total: Option<usize> = nums.iter().map(|w| w.parse::<usize>().ok()).product();
assert_eq!(total, Some(100));
let nums = vec!["5", "10", "one", "2"];
let total: Option<usize> = nums.iter().map(|w| w.parse::<usize>().ok()).product();
assert_eq!(total, None);

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impl<T> Residual<T> for Option<Infallible>

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type TryType = Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2_residual)

The “return” type of this meta-function.

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fn sum(iter: I) -> Option<T>
where I: Iterator<Item = Option>,

Takes each element in the Iterator: if it is a None, no further elements are taken, and the None is returned. Should no None occur, the sum of all elements is returned.

§Examples

This sums up the position of the character ‘a’ in a vector of strings, if a word did not have the character ‘a’ the operation returns None:

let words = vec!["have", "a", "great", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, Some(5));
let words = vec!["have", "a", "good", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, None);

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impl<T> Try for Option<T>

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type Output = T

🔬This is a nightly-only experimental API. (try_trait_v2)

The type of the value produced by ? when not short-circuiting.

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type Residual = Option<Infallible>

🔬This is a nightly-only experimental API. (try_trait_v2)

The type of the value passed to FromResidual::from_residual as part of ? when short-circuiting. Read more

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fn from_output(output: <Option<T> as Try>::Output) -> Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2)

Constructs the type from its Output type. Read more

source §

fn branch( self, ) -> ControlFlow<<Option<T> as Try>::Residual, <Option<T> as Try>::Output>

🔬This is a nightly-only experimental API. (try_trait_v2)

Used in ? to decide whether the operator should produce a value (because this returned ControlFlow::Continue) or propagate a value back to the caller (because this returned ControlFlow::Break). Read more

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impl<T> TypeInfo for Option<T>
where T: TypeInfo + 'static,

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type Identity = Option<T>

The type identifying for which type info is provided. Read more

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fn type_info() -> Type

Returns the static type identifier for Self.

Decode Self and consume all of the given input data. Read more

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impl<T> DecodeLimit for T
where T: Decode,

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fn decode_all_with_depth_limit( limit: u32, input: &mut &[u8], ) -> Result<T, Error>

Decode Self and consume all of the given input data. Read more

Variants§

None

Some(T)

Implementations§

impl<T> Option<T>

pub const fn is_some(&self) -> bool

§Examples

pub fn is_some_and(self, f: impl FnOnce(T) -> bool) -> bool

§Examples

pub const fn is_none(&self) -> bool

§Examples

pub fn is_none_or(self, f: impl FnOnce(T) -> bool) -> bool

§Examples

pub const fn as_ref(&self) -> Option<&T>

§Examples

pub fn as_mut(&mut self) -> Option<&mut T>

§Examples

pub fn as_pin_ref(self: Pin<&Option<T>>) -> Option<Pin<&T>>

pub fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&mut T>>

pub fn as_slice(&self) -> &[T]

§Examples

pub fn as_mut_slice(&mut self) -> &mut [T]

§Examples

pub fn expect(self, msg: &str) -> T

§Panics

§Examples

§Recommended Message Style

pub fn unwrap(self) -> T

§Panics

§Examples

pub fn unwrap_or(self, default: T) -> T

§Examples

pub fn unwrap_or_else<F>(self, f: F) -> Twhere F: FnOnce() -> T,

§Examples

pub fn unwrap_or_default(self) -> Twhere T: Default,

§Examples

pub unsafe fn unwrap_unchecked(self) -> T

§Safety

§Examples

pub fn map<U, F>(self, f: F) -> Option<U>where F: FnOnce(T) -> U,

§Examples

pub fn inspect<F>(self, f: F) -> Option<T>where F: FnOnce(&T),

§Examples

pub fn map_or<U, F>(self, default: U, f: F) -> Uwhere F: FnOnce(T) -> U,

§Examples

pub fn map_or_else<U, D, F>(self, default: D, f: F) -> Uwhere D: FnOnce() -> U, F: FnOnce(T) -> U,

§Basic examples

§Handling a Result-based fallback

pub fn ok_or<E>(self, err: E) -> Result<T, E>

§Examples

pub fn ok_or_else<E, F>(self, err: F) -> Result<T, E>where F: FnOnce() -> E,

§Examples

pub fn as_deref(&self) -> Option<&<T as Deref>::Target>where T: Deref,

§Examples

pub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::Target>where T: DerefMut,

§Examples

pub fn iter(&self) -> Iter<'_, T> ⓘ

§Examples

pub fn iter_mut(&mut self) -> IterMut<'_, T> ⓘ

§Examples

pub fn and<U>(self, optb: Option<U>) -> Option<U>

§Examples

pub fn and_then<U, F>(self, f: F) -> Option<U>where F: FnOnce(T) -> Option<U>,

§Examples

pub fn filter<P>(self, predicate: P) -> Option<T>where P: FnOnce(&T) -> bool,

§Examples

pub fn or(self, optb: Option<T>) -> Option<T>

§Examples

pub fn or_else<F>(self, f: F) -> Option<T>where F: FnOnce() -> Option<T>,

§Examples

pub fn xor(self, optb: Option<T>) -> Option<T>

§Examples

pub fn insert(&mut self, value: T) -> &mut T

§Example

pub fn get_or_insert(&mut self, value: T) -> &mut T

§Examples

pub fn get_or_insert_default(&mut self) -> &mut Twhere T: Default,

§Examples

pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut Twhere F: FnOnce() -> T,

Enum gstd::prelude::Option

pub fn unwrap_or_else<F>(self, f: F) -> T
where F: FnOnce() -> T,

pub fn unwrap_or_default(self) -> T
where T: Default,

pub fn map<U, F>(self, f: F) -> Option<U>
where F: FnOnce(T) -> U,

pub fn inspect<F>(self, f: F) -> Option<T>
where F: FnOnce(&T),

pub fn map_or<U, F>(self, default: U, f: F) -> U
where F: FnOnce(T) -> U,

pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U
where D: FnOnce() -> U, F: FnOnce(T) -> U,

pub fn ok_or_else<E, F>(self, err: F) -> Result<T, E>
where F: FnOnce() -> E,

pub fn as_deref(&self) -> Option<&<T as Deref>::Target>
where T: Deref,

pub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::Target>
where T: DerefMut,

pub fn and_then<U, F>(self, f: F) -> Option<U>
where F: FnOnce(T) -> Option<U>,

pub fn filter<P>(self, predicate: P) -> Option<T>
where P: FnOnce(&T) -> bool,

pub fn or_else<F>(self, f: F) -> Option<T>
where F: FnOnce() -> Option<T>,

pub fn get_or_insert_default(&mut self) -> &mut T
where T: Default,

pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T
where F: FnOnce() -> T,

pub fn take_if<P>(&mut self, predicate: P) -> Option<T>
where P: FnOnce(&mut T) -> bool,

pub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>
where F: FnOnce(T, U) -> R,

pub fn copied(self) -> Option<T>
where T: Copy,

pub fn cloned(self) -> Option<T>
where T: Clone,

pub fn copied(self) -> Option<T>
where T: Copy,

pub fn cloned(self) -> Option<T>
where T: Clone,

fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,

fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,

fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,

fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,

fn as_bytes_mut(&mut self) -> &mut [u8]
where Self: FromBytes,