core::ops::Deref - Rust
Description: API documentation for the Rust `Deref` trait in crate `core`.
Keywords: rust, rustlang, rust-lang, Deref

# Trait core::ops::Deref 1.0.0 [−] [src]

    #[lang = "deref"]
    pub trait Deref {
        type Target: ?Sized;
        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 accomodate 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 as well as the reference sections on the dereference operator, the `Deref` trait, 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) -> &T {
            &self.value
        }
    }

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

## Associated Types

### `type Target: ?Sized`

The resulting type after dereferencing.

## Required Methods

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

Dereferences the value.

## Implementors

- [src]
  `impl<T> Deref for ManuallyDrop<T> type Target = T;`
- `impl<'a, T: ?Sized> Deref for &'a T type Target = T;`
- `impl<'a, T: ?Sized> Deref for &'a mut T type Target = T;`
- [src]
  `impl<'b, T: ?Sized> Deref for Ref<'b, T> type Target = T;`
- [src]
  `impl<'b, T: ?Sized> Deref for RefMut<'b, T> type Target = T;`

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