1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199

/// 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'][more]. 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*][book]
/// as well as the reference sections on [the dereference operator][ref-deref-op],
/// [method resolution] and [type coercions].
///
/// [book]: ../../book/ch15-02-deref.html
/// [more]: #more-on-deref-coercion
/// [ref-deref-op]: ../../reference/expressions/operator-expr.html#the-dereference-operator
/// [method resolution]: ../../reference/expressions/method-call-expr.html
/// [type coercions]: ../../reference/type-coercions.html
///
/// # 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);
/// ```
#[lang = "deref"]
#[doc(alias = "*")]
#[doc(alias = "&*")]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "Deref"]
pub trait Deref {
    /// The resulting type after dereferencing.
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_diagnostic_item = "deref_target"]
    #[lang = "deref_target"]
    type Target: ?Sized;

    /// Dereferences the value.
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_diagnostic_item = "deref_method"]
    fn deref(&self) -> &Self::Target;
}

#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
impl<T: ?Sized> const Deref for &T {
    type Target = T;

    #[rustc_diagnostic_item = "noop_method_deref"]
    fn deref(&self) -> &T {
        *self
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> !DerefMut for &T {}

#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
impl<T: ?Sized> const Deref for &mut T {
    type Target = T;

    fn deref(&self) -> &T {
        *self
    }
}

/// Used for mutable dereferencing operations, like in `*v = 1;`.
///
/// In addition to being used for explicit dereferencing operations with the
/// (unary) `*` operator in mutable contexts, `DerefMut` is also used implicitly
/// by the compiler in many circumstances. This mechanism is called
/// ['`Deref` coercion'][more]. In immutable contexts, [`Deref`] is used.
///
/// Implementing `DerefMut` for smart pointers makes mutating the data behind
/// them convenient, which is why they implement `DerefMut`. On the other hand,
/// the rules regarding [`Deref`] and `DerefMut` were designed specifically to
/// accommodate smart pointers. Because of this, **`DerefMut` 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 `DerefMut` is invoked
/// implicitly.
///
/// # More on `Deref` coercion
///
/// If `T` implements `DerefMut<Target = U>`, and `x` is a value of type `T`,
/// then:
///
/// * In mutable contexts, `*x` (where `T` is neither a reference nor a raw pointer)
///   is equivalent to `*DerefMut::deref_mut(&mut x)`.
/// * Values of type `&mut T` are coerced to values of type `&mut U`
/// * `T` implicitly implements all the (mutable) 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].
///
/// [book]: ../../book/ch15-02-deref.html
/// [more]: #more-on-deref-coercion
/// [ref-deref-op]: ../../reference/expressions/operator-expr.html#the-dereference-operator
/// [method resolution]: ../../reference/expressions/method-call-expr.html
/// [type coercions]: ../../reference/type-coercions.html
///
/// # Examples
///
/// A struct with a single field which is modifiable by dereferencing the
/// struct.
///
/// ```
/// use std::ops::{Deref, DerefMut};
///
/// struct DerefMutExample<T> {
///     value: T
/// }
///
/// impl<T> Deref for DerefMutExample<T> {
///     type Target = T;
///
///     fn deref(&self) -> &Self::Target {
///         &self.value
///     }
/// }
///
/// impl<T> DerefMut for DerefMutExample<T> {
///     fn deref_mut(&mut self) -> &mut Self::Target {
///         &mut self.value
///     }
/// }
///
/// let mut x = DerefMutExample { value: 'a' };
/// *x = 'b';
/// assert_eq!('b', x.value);
/// ```
#[lang = "deref_mut"]
#[doc(alias = "*")]
#[stable(feature = "rust1", since = "1.0.0")]
pub trait DerefMut: Deref {
    /// Mutably dereferences the value.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn deref_mut(&mut self) -> &mut Self::Target;
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> DerefMut for &mut T {
    fn deref_mut(&mut self) -> &mut T {
        *self
    }
}

/// Indicates that a struct can be used as a method receiver, without the
/// `arbitrary_self_types` feature. This is implemented by stdlib pointer types like `Box<T>`,
/// `Rc<T>`, `&T`, and `Pin<P>`.
#[lang = "receiver"]
#[unstable(feature = "receiver_trait", issue = "none")]
#[doc(hidden)]
pub trait Receiver {
    // Empty.
}

#[unstable(feature = "receiver_trait", issue = "none")]
impl<T: ?Sized> Receiver for &T {}

#[unstable(feature = "receiver_trait", issue = "none")]
impl<T: ?Sized> Receiver for &mut T {}
This documentation is an old archive. Please see https://rust.docs.kernel.org instead.