Trait gstd::prelude::AsRef

1.0.0 · source ·
pub trait AsRef<T>
where T: ?Sized,
{ // Required method fn as_ref(&self) -> &T; }
Expand description

Used to do a cheap reference-to-reference conversion.

This trait is similar to AsMut which is used for converting between mutable references. If you need to do a costly conversion it is better to implement From with type &T or write a custom function.

§Relation to Borrow

AsRef has the same signature as Borrow, but Borrow is different in a few aspects:

  • Unlike AsRef, Borrow has a blanket impl for any T, and can be used to accept either a reference or a value. (See also note on AsRef’s reflexibility below.)
  • Borrow also requires that Hash, Eq and Ord for a borrowed value are equivalent to those of the owned value. For this reason, if you want to borrow only a single field of a struct you can implement AsRef, but not Borrow.

Note: This trait must not fail. If the conversion can fail, use a dedicated method which returns an Option<T> or a Result<T, E>.

§Generic Implementations

AsRef auto-dereferences if the inner type is a reference or a mutable reference (e.g.: foo.as_ref() will work the same if foo has type &mut Foo or &&mut Foo).

Note that due to historic reasons, the above currently does not hold generally for all dereferenceable types, e.g. foo.as_ref() will not work the same as Box::new(foo).as_ref(). Instead, many smart pointers provide an as_ref implementation which simply returns a reference to the pointed-to value (but do not perform a cheap reference-to-reference conversion for that value). However, AsRef::as_ref should not be used for the sole purpose of dereferencing; instead Deref coercion’ can be used:

let x = Box::new(5i32);
// Avoid this:
// let y: &i32 = x.as_ref();
// Better just write:
let y: &i32 = &x;

Types which implement Deref should consider implementing AsRef<T> as follows:

impl<T> AsRef<T> for SomeType
where
    T: ?Sized,
    <SomeType as Deref>::Target: AsRef<T>,
{
    fn as_ref(&self) -> &T {
        self.deref().as_ref()
    }
}

§Reflexivity

Ideally, AsRef would be reflexive, i.e. there would be an impl<T: ?Sized> AsRef<T> for T with as_ref simply returning its argument unchanged. Such a blanket implementation is currently not provided due to technical restrictions of Rust’s type system (it would be overlapping with another existing blanket implementation for &T where T: AsRef<U> which allows AsRef to auto-dereference, see “Generic Implementations” above).

A trivial implementation of AsRef<T> for T must be added explicitly for a particular type T where needed or desired. Note, however, that not all types from std contain such an implementation, and those cannot be added by external code due to orphan rules.

§Examples

By using trait bounds we can accept arguments of different types as long as they can be converted to the specified type T.

For example: By creating a generic function that takes an AsRef<str> we express that we want to accept all references that can be converted to &str as an argument. Since both String and &str implement AsRef<str> we can accept both as input argument.

fn is_hello<T: AsRef<str>>(s: T) {
   assert_eq!("hello", s.as_ref());
}

let s = "hello";
is_hello(s);

let s = "hello".to_string();
is_hello(s);

Required Methods§

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fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.

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impl AsRef<str> for str

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impl AsRef<str> for String

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impl AsRef<MessageHandle> for MessageHandle

1.7.0 · source§

impl AsRef<CStr> for CStr

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impl AsRef<CStr> for CString

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impl AsRef<OsStr> for Component<'_>

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impl AsRef<OsStr> for str

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impl AsRef<OsStr> for OsStr

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impl AsRef<OsStr> for OsString

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impl AsRef<OsStr> for Components<'_>

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impl AsRef<OsStr> for std::path::Iter<'_>

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impl AsRef<OsStr> for Path

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impl AsRef<OsStr> for PathBuf

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impl AsRef<OsStr> for String

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impl AsRef<Path> for Cow<'_, OsStr>

1.25.0 · source§

impl AsRef<Path> for Component<'_>

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impl AsRef<Path> for str

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impl AsRef<Path> for OsStr

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impl AsRef<Path> for OsString

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impl AsRef<Path> for Components<'_>

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impl AsRef<Path> for std::path::Iter<'_>

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impl AsRef<Path> for Path

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impl AsRef<Path> for PathBuf

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impl AsRef<Path> for String

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impl AsRef<[u8]> for str

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impl AsRef<[u8]> for ActorId

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impl AsRef<[u8]> for CodeId

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impl AsRef<[u8]> for MessageId

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impl AsRef<[u8]> for ReservationId

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impl AsRef<[u8]> for String

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impl AsRef<[u8]> for Bytes

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impl AsRef<[u8]> for BytesMut

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impl AsRef<[u8]> for H128

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impl AsRef<[u8]> for H160

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impl AsRef<[u8]> for H256

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impl AsRef<[u8]> for H384

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impl AsRef<[u8]> for H512

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impl AsRef<[u8]> for H768

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impl AsRef<[u64]> for U128

Get a reference to the underlying little-endian words.

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impl AsRef<[u64]> for U256

Get a reference to the underlying little-endian words.

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impl AsRef<[u64]> for U512

Get a reference to the underlying little-endian words.

1.55.0 · source§

impl<'a> AsRef<str> for gstd::prelude::string::Drain<'a>

1.55.0 · source§

impl<'a> AsRef<[u8]> for gstd::prelude::string::Drain<'a>

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impl<'a, T> AsRef<T> for MutexGuard<'a, T>

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impl<'a, T> AsRef<T> for RwLockReadGuard<'a, T>

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impl<'a, T> AsRef<T> for RwLockWriteGuard<'a, T>

1.46.0 · source§

impl<'a, T, A> AsRef<[T]> for gstd::prelude::vec::Drain<'a, T, A>
where A: Allocator,

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impl<'a, T, A> AsRef<[T]> for Drain<'a, T, A>
where A: Allocator,

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impl<A, O> AsRef<BitSlice<<A as BitView>::Store, O>> for BitArray<A, O>
where A: BitViewSized, O: BitOrder,

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impl<M, T, O> AsRef<bool> for BitRef<'_, M, T, O>
where M: Mutability, T: BitStore, O: BitOrder,

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impl<T> AsRef<[T]> for [T]

1.13.0 · source§

impl<T> AsRef<[T]> for gstd::prelude::slice::Iter<'_, T>

1.53.0 · source§

impl<T> AsRef<[T]> for gstd::prelude::slice::IterMut<'_, T>

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impl<T> AsRef<T> for Cow<'_, T>
where T: ToOwned + ?Sized,

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impl<T> AsRef<T> for FmtBinary<T>
where T: Binary,

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impl<T> AsRef<T> for FmtDisplay<T>
where T: Display,

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impl<T> AsRef<T> for FmtList<T>
where &'a T: for<'a> IntoIterator,

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impl<T> AsRef<T> for FmtLowerExp<T>
where T: LowerExp,

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impl<T> AsRef<T> for FmtLowerHex<T>
where T: LowerHex,

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impl<T> AsRef<T> for FmtOctal<T>
where T: Octal,

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impl<T> AsRef<T> for FmtPointer<T>
where T: Pointer,

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impl<T> AsRef<T> for FmtUpperExp<T>
where T: UpperExp,

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impl<T> AsRef<T> for FmtUpperHex<T>
where T: UpperHex,

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impl<T> AsRef<[u8]> for Window<T>
where T: AsRef<[u8]>,

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impl<T, A> AsRef<[T]> for gstd::prelude::Vec<T, A>
where A: Allocator,

1.46.0 · source§

impl<T, A> AsRef<[T]> for gstd::prelude::vec::IntoIter<T, A>
where A: Allocator,

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impl<T, A> AsRef<[T]> for IntoIter<T, A>
where A: Allocator,

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impl<T, A> AsRef<[T]> for Vec<T, A>
where A: Allocator,

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impl<T, A> AsRef<Vec<T, A>> for gstd::prelude::Vec<T, A>
where A: Allocator,

1.5.0 · source§

impl<T, A> AsRef<T> for Arc<T, A>
where A: Allocator, T: ?Sized,

1.5.0 · source§

impl<T, A> AsRef<T> for Rc<T, A>
where A: Allocator, T: ?Sized,

1.5.0 · source§

impl<T, A> AsRef<T> for gstd::prelude::Box<T, A>
where A: Allocator, T: ?Sized,

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impl<T, A> AsRef<T> for Box<T, A>
where A: Allocator, T: ?Sized,

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impl<T, A> AsRef<Vec<T, A>> for Vec<T, A>
where A: Allocator,

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impl<T, O> AsRef<BitSlice<<T as BitStore>::Alias, O>> for IterMut<'_, T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> AsRef<BitSlice<T, O>> for BitBox<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> AsRef<BitSlice<T, O>> for BitSlice<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> AsRef<BitSlice<T, O>> for BitVec<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> AsRef<BitSlice<T, O>> for Drain<'_, T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> AsRef<BitSlice<T, O>> for IntoIter<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> AsRef<BitSlice<T, O>> for Iter<'_, T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> AsRef<BitVec<T, O>> for BitVec<T, O>
where T: BitStore, O: BitOrder,

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impl<T, U> AsRef<U> for &T
where T: AsRef<U> + ?Sized, U: ?Sized,

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impl<T, U> AsRef<U> for &mut T
where T: AsRef<U> + ?Sized, U: ?Sized,

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impl<T, const CAP: usize> AsRef<[T]> for ArrayVec<T, CAP>

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impl<T, const N: usize> AsRef<[T; N]> for Simd<T, N>

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impl<T, const N: usize> AsRef<[T]> for [T; N]

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impl<T, const N: usize> AsRef<[T]> for Simd<T, N>

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impl<const CAP: usize> AsRef<str> for ArrayString<CAP>