Trait core::ops::Deref

1.0.0 · source · 
pub trait Deref {
    type Target: ?Sized;

    fn deref(&self) -> &Self::Target;
}
Expand description

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 (where T is neither a reference nor a raw pointer) 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, 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);
Run

Required Associated Types

The resulting type after dereferencing.

Required Methods

Dereferences the value.

Implementors

impl<T: ?Sized> Deref for ThinBox<T>

impl<T: ?Sized, A: Allocator> Deref for Box<T, A>

impl<B: ?Sized + ToOwned> Deref for Cow<'_, B>where
    B::Owned: Borrow<B>,

impl<T: Ord> Deref for PeekMut<'_, T>

impl Deref for CString

impl<T: ?Sized> Deref for Rc<T>

impl Deref for String

impl<T: ?Sized> Deref for Arc<T>

impl<T, A: Allocator> Deref for Vec<T, A>

impl Deref for OsString

impl<'a> Deref for IoSliceMut<'a>

impl<'a> Deref for IoSlice<'a>

impl Deref for PathBuf

impl<T, F: FnOnce() -> T> Deref for LazyLock<T, F>

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

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

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