Trait core::ops::Deref

#[lang = "deref"]
pub trait Deref {
    type Target: ?Sized;
#[must_use]
    fn deref(&self) -> &Self::Target;
}

Used for immutable dereferencing operations, like *v.

In addition to being used for explicit dereferencing operations with the (unary) * operator in immutable contexts, Deref is also used implicitly by the compiler in many circumstances. This mechanism is called 'Deref coercion'. In mutable contexts, DerefMut is used.

Implementing Deref for smart pointers makes accessing the data behind them convenient, which is why they implement Deref. On the other hand, the rules regarding Deref and DerefMut were designed specifically to accommodate smart pointers. Because of this, Deref should only be implemented for smart pointers to avoid confusion.

For similar reasons, this trait should never fail. Failure during dereferencing can be extremely confusing when Deref is invoked implicitly.

More on Deref coercion

If T implements Deref<Target = U>, and x is a value of type T, then:

• In immutable contexts, *x on non-pointer types is equivalent to *Deref::deref(&x).
• Values of type &T are coerced to values of type &U
• T implicitly implements all the (immutable) methods of the type U.

For more details, visit [the chapter in The Rust Programming Language] book as well as the reference sections on [the dereference operator] ref-deref-op, method resolution and type coercions.

Examples

A struct with a single field which is accessible by dereferencing the struct.

use std::ops::Deref;

struct DerefExample<T> {
    value: T
}

impl<T> Deref for DerefExample<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.value
    }
}

let x = DerefExample { value: 'a' };
assert_eq!('a', *x);

Associated Types

type Target: ?Sized

The resulting type after dereferencing.

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Required methods

#[must_use]

fn deref(&self) -> &Self::Target

Dereferences the value.

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Implementors

impl<P: Deref> Deref for Pin<P>

type Target = P::Target

fn deref(&self) -> &P::Target

impl<T: ?Sized> Deref for ManuallyDrop<T>

type Target = T

fn deref(&self) -> &T

impl<T: ?Sized, '_> Deref for &'_ T

type Target = T

fn deref(&self) -> &T

impl<T: ?Sized, '_> Deref for &'_ mut T

type Target = T

fn deref(&self) -> &T

impl<T: ?Sized, '_> Deref for Ref<'_, T>

type Target = T

fn deref(&self) -> &T

impl<T: ?Sized, '_> Deref for RefMut<'_, T>

type Target = T

fn deref(&self) -> &T

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