Trait std::ops::Deref

#[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 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 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) -> &T {
        &self.value
    }
}

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

Associated Types

type Target: ?Sized

The resulting type after dereferencing.

Required Methods

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

Dereferences the value.

Implementors

• impl<'a, T> Deref for &'a mut T where
    T: ?Sized,  type Target = T;
• impl<'b, T> Deref for Ref<'b, T> where
    T: ?Sized,  type Target = T;
• impl<'a, T> Deref for &'a T where
    T: ?Sized,  type Target = T;
• impl<'b, T> Deref for RefMut<'b, T> where
    T: ?Sized,  type Target = T;
• impl<T> Deref for ManuallyDrop<T> type Target = T;
• impl Deref for String type Target = str;
• impl<T> Deref for Rc<T> where
    T: ?Sized,  type Target = T;
• impl<'a, B> Deref for Cow<'a, B> where
    B: ToOwned + ?Sized,  type Target = B;
• impl<T> Deref for Vec<T> type Target = [T];
• impl<'a, T> Deref for PeekMut<'a, T> where
    T: Ord,  type Target = T;
• impl<T> Deref for Arc<T> where
    T: ?Sized,  type Target = T;
• impl<T> Deref for Box<T> where
    T: ?Sized,  type Target = T;
• impl Deref for CString type Target = CStr;
• impl Deref for OsString type Target = OsStr;
• impl<T> Deref for AssertUnwindSafe<T> type Target = T;
• impl Deref for PathBuf type Target = Path;
• impl<'mutex, T: ?Sized> Deref for MutexGuard<'mutex, T> type Target = T;
• impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> type Target = T;
• impl<'rwlock, T: ?Sized> Deref for RwLockWriteGuard<'rwlock, T> type Target = T;