1.0.0[−][src]Trait core::convert::AsRef
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.
AsRef
has the same signature as Borrow
, but Borrow
is different in few aspects:
- Unlike
AsRef
,Borrow
has a blanket impl for anyT
, and can be used to accept either a reference or a value. Borrow
also requires thatHash
,Eq
andOrd
for 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 implementAsRef
, but notBorrow
.
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 iffoo
has type&mut Foo
or&&mut Foo
)
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);Run
Required methods
fn as_ref(&self) -> &T
Performs the conversion.
Implementors
impl AsRef<[u8]> for str
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impl AsRef<str> for str
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impl<'_, T> AsRef<[T]> for Iter<'_, T>
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impl<'_, T: ?Sized, U: ?Sized> AsRef<U> for &'_ T where
T: AsRef<U>,
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T: AsRef<U>,
impl<'_, T: ?Sized, U: ?Sized> AsRef<U> for &'_ mut T where
T: AsRef<U>,
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T: AsRef<U>,
impl<T> AsRef<[T]> for [T]
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impl<T, const N: usize> AsRef<[T]> for [T; N] where
[T; N]: LengthAtMost32,
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[T; N]: LengthAtMost32,