1.0.0[−][src]Trait alloc::prelude::v1::AsRef

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);

Required methods

ⓘImportant traits for &'_ mut I

fn as_ref(&self) -> &T

Performs the conversion.

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Implementations on Foreign Types

impl<'a> AsRef<OsStr> for Component<'a>
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impl AsRef<Path> for OsStr
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impl AsRef<OsStr> for OsString
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impl<'a> AsRef<OsStr> for Components<'a>
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impl AsRef<Path> for OsString
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impl AsRef<CStr> for CStr
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impl AsRef<OsStr> for OsStr
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impl AsRef<Path> for str
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impl<'a> AsRef<Path> for Components<'a>
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impl<'a> AsRef<Path> for Component<'a>
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impl AsRef<OsStr> for String
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impl<'a> AsRef<Path> for Cow<'a, OsStr>
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impl AsRef<OsStr> for str
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impl AsRef<OsStr> for Path
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impl AsRef<CStr> for CString
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impl<'a> AsRef<OsStr> for Iter<'a>
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impl AsRef<OsStr> for PathBuf
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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<'a> AsRef<Path> for Iter<'a>
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impl<T> AsRef<[T]> for [T; 10]
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impl<T> AsRef<[T]> for [T; 24]
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impl<T> AsRef<[T]> for [T; 5]
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impl<T> AsRef<[T]> for [T; 28]
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impl<T> AsRef<[T]> for [T; 16]
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impl<T> AsRef<[T]> for [T; 23]
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impl<T> AsRef<[T]> for [T; 30]
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impl<T> AsRef<[T]> for [T; 26]
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impl<T> AsRef<[T]> for [T; 32]
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impl AsRef<str> for str
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impl<T> AsRef<[T]> for [T]
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impl<T> AsRef<[T]> for [T; 25]
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impl<T> AsRef<[T]> for [T; 11]
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impl<T> AsRef<[T]> for [T; 15]
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impl<T> AsRef<[T]> for [T; 13]
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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> AsRef<[T]> for [T; 27]
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impl<T> AsRef<[T]> for [T; 3]
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impl<T> AsRef<[T]> for [T; 8]
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impl<T> AsRef<[T]> for [T; 1]
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impl<T> AsRef<[T]> for [T; 2]
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impl<T> AsRef<[T]> for [T; 22]
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impl<T> AsRef<[T]> for [T; 19]
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impl<'_, T, U> AsRef<U> for &'_ T where
    T: AsRef<U> + ?Sized,
    U: ?Sized, 
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impl<T> AsRef<[T]> for [T; 7]
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impl<T> AsRef<[T]> for [T; 29]
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impl AsRef<[u8]> for str
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impl<T> AsRef<[T]> for [T; 6]
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impl<T> AsRef<[T]> for [T; 4]
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impl<T> AsRef<[T]> for [T; 17]
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impl<T> AsRef<[T]> for [T; 14]
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impl<T> AsRef<[T]> for [T; 18]
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impl<T> AsRef<[T]> for [T; 20]
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impl<T> AsRef<[T]> for [T; 21]
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impl<T> AsRef<[T]> for [T; 9]
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impl<T> AsRef<[T]> for [T; 12]
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impl<T> AsRef<[T]> for [T; 31]
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impl<T> AsRef<[T]> for [T; 0]
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impl<T> AsRef<T> for Arc<T> where
    T: ?Sized, 
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impl<T> AsRef<Vec<T>> for Vec<T>
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impl<T> AsRef<T> for Rc<T> where
    T: ?Sized, 
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impl<'a, T> AsRef<T> for Cow<'a, T> where
    T: ToOwned + ?Sized, 
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impl<T> AsRef<[T]> for Vec<T>
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impl<T> AsRef<T> for Box<T> where
    T: ?Sized, 
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impl AsRef<[u8]> for String
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impl AsRef<str> for String
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Implementors

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