std::convert::AsRef - Rust
Description: API documentation for the Rust `AsRef` trait in crate `std`.
Keywords: rust, rustlang, rust-lang, AsRef

# Trait std::convert::AsRef 1.0.0[−][src]

    pub trait AsRef<T> where
        T: ?Sized, {
        fn as_ref(&self) -> &T;
    }

A cheap reference-to-reference conversion. Used to convert a value to a reference value within generic code.

`AsRef` is very similar to, but serves a slightly different purpose than, `Borrow`.

`AsRef` is to be used when wishing to convert to a reference of another type. `Borrow` is more related to the notion of taking the reference. It is useful when wishing to abstract over the type of reference (`&T`, `&mut T`) or allow both the referenced and owned type to be treated in the same manner.

The key difference between the two traits is the intention:

- Use `AsRef` when the goal is to simply convert into a reference
- Use `Borrow` when the goal is related to writing code that is agnostic to the type of borrow and whether it is a reference or value

See the book for a more detailed comparison.

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`)

# Examples

Both `String` and `&str` implement `AsRef<str>`:

    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);Run

## Required Methods

ⓘImportant traits for &'a mut I

### Important traits for &'a mut I

`impl<'a, I> Iterator for &'a mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`

### `fn as_ref(&self) -> &T`

Performs the conversion.

## Implementors

- `impl<T> AsRef<[T]> for [T; 9]` | [src]

- `impl<T> AsRef<[T]> for [T; 21]` | [src]

- `impl<T> AsRef<[T]> for [T; 25]` | [src]

- `impl<T> AsRef<[T]> for [T; 23]` | [src]

- `impl<'a, T> AsRef<[T]> for std::slice::Iter<'a, T>` | [src]

- `impl<T> AsRef<[T]> for [T; 10]` | [src]

- `impl<T> AsRef<[T]> for [T; 24]` | [src]

- `impl<T> AsRef<[T]> for [T; 1]` | [src]

- `impl<T> AsRef<[T]> for [T; 6]` | [src]

- `impl<T> AsRef<[T]> for [T; 29]` | [src]

- `impl<T> AsRef<[T]> for [T; 11]` | [src]

- `impl<T> AsRef<[T]> for [T; 8]` | [src]

- `impl<T> AsRef<[T]> for [T; 32]` | [src]

- `impl<T> AsRef<[T]> for [T; 18]` | [src]

- `impl<'a, T, U> AsRef<U> for &'a mut T where T: AsRef<U> + ?Sized, U: ?Sized,` | [src]

- `impl<T> AsRef<[T]> for [T; 20]` | [src]

- `impl<T> AsRef<[T]> for [T; 0]` | [src]

- `impl<T> AsRef<[T]> for [T; 27]` | [src]

- `impl<T> AsRef<[T]> for [T; 28]` | [src]

- `impl<T> AsRef<[T]> for [T; 4]` | [src]

- `impl<T> AsRef<[T]> for [T]` | [src]

- `impl<T> AsRef<[T]> for [T; 2]` | [src]

- `impl<T> AsRef<[T]> for [T; 30]` | [src]

- `impl<T> AsRef<[T]> for [T; 17]` | [src]

- `impl<T> AsRef<[T]> for [T; 26]` | [src]

- `impl<T> AsRef<[T]> for [T; 7]` | [src]

- `impl AsRef<[u8]> for str` | [src]

- `impl<T> AsRef<[T]> for [T; 13]` | [src]

- `impl<T> AsRef<[T]> for [T; 15]` | [src]

- `impl<T> AsRef<[T]> for [T; 5]` | [src]

- `impl<T> AsRef<[T]> for [T; 22]` | [src]

- `impl<T> AsRef<[T]> for [T; 14]` | [src]

- `impl<T> AsRef<[T]> for [T; 12]` | [src]

- `impl<'a, T, U> AsRef<U> for &'a T where T: AsRef<U> + ?Sized, U: ?Sized,` | [src]

- `impl<T> AsRef<[T]> for [T; 19]` | [src]

- `impl AsRef<str> for str` | [src]

- `impl<T> AsRef<[T]> for [T; 16]` | [src]

- `impl<T> AsRef<[T]> for [T; 31]` | [src]

- `impl<T> AsRef<[T]> for [T; 3]` | [src]

- `impl<T> AsRef<T> for Box<T> where T: ?Sized,` | [src]

- `impl<T> AsRef<Vec<T>> for Vec<T>` | [src]

- `impl<'a, T> AsRef<T> for Cow<'a, T> where T: ToOwned + ?Sized,` | [src]

- `impl<T> AsRef<T> for Arc<T> where T: ?Sized,` | [src]

- `impl AsRef<[u8]> for String` | [src]

- `impl<T> AsRef<T> for Rc<T> where T: ?Sized,` | [src]

- `impl<T> AsRef<[T]> for Vec<T>` | [src]

- `impl AsRef<str> for String` | [src]

- `impl AsRef<CStr> for CStr` | [src]

- `impl AsRef<CStr> for CString` | [src]

- `impl AsRef<OsStr> for OsStr` | [src]

- `impl AsRef<OsStr> for OsString` | [src]

- `impl AsRef<OsStr> for str` | [src]

- `impl AsRef<OsStr> for String` | [src]

- `impl<'a> AsRef<OsStr> for Component<'a>` | [src]

- `impl<'a> AsRef<Path> for Component<'a>` | [src]

- `impl<'a> AsRef<Path> for Components<'a>` | [src]

- `impl<'a> AsRef<OsStr> for Components<'a>` | [src]

- `impl<'a> AsRef<Path> for std::path::Iter<'a>` | [src]

- `impl<'a> AsRef<OsStr> for std::path::Iter<'a>` | [src]

- `impl AsRef<OsStr> for PathBuf` | [src]

- `impl AsRef<OsStr> for Path` | [src]

- `impl AsRef<Path> for Path` | [src]

- `impl AsRef<Path> for OsStr` | [src]

- `impl<'a> AsRef<Path> for Cow<'a, OsStr>` | [src]

- `impl AsRef<Path> for OsString` | [src]

- `impl AsRef<Path> for str` | [src]

- `impl AsRef<Path> for String` | [src]

- `impl AsRef<Path> for PathBuf` | [src]

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