1 //! Overloadable operators. 2 //! 3 //! Implementing these traits allows you to overload certain operators. 4 //! 5 //! Some of these traits are imported by the prelude, so they are available in 6 //! every Rust program. Only operators backed by traits can be overloaded. For 7 //! example, the addition operator (`+`) can be overloaded through the [`Add`] 8 //! trait, but since the assignment operator (`=`) has no backing trait, there 9 //! is no way of overloading its semantics. Additionally, this module does not 10 //! provide any mechanism to create new operators. If traitless overloading or 11 //! custom operators are required, you should look toward macros or compiler 12 //! plugins to extend Rust's syntax. 13 //! 14 //! Implementations of operator traits should be unsurprising in their 15 //! respective contexts, keeping in mind their usual meanings and 16 //! [operator precedence]. For example, when implementing [`Mul`], the operation 17 //! should have some resemblance to multiplication (and share expected 18 //! properties like associativity). 19 //! 20 //! Note that the `&&` and `||` operators are currently not supported for 21 //! overloading. Due to their short circuiting nature, they require a different 22 //! design from traits for other operators like [`BitAnd`]. Designs for them are 23 //! under discussion. 24 //! 25 //! Many of the operators take their operands by value. In non-generic 26 //! contexts involving built-in types, this is usually not a problem. 27 //! However, using these operators in generic code, requires some 28 //! attention if values have to be reused as opposed to letting the operators 29 //! consume them. One option is to occasionally use [`clone`]. 30 //! Another option is to rely on the types involved providing additional 31 //! operator implementations for references. For example, for a user-defined 32 //! type `T` which is supposed to support addition, it is probably a good 33 //! idea to have both `T` and `&T` implement the traits [`Add<T>`][`Add`] and 34 //! [`Add<&T>`][`Add`] so that generic code can be written without unnecessary 35 //! cloning. 36 //! 37 //! # Examples 38 //! 39 //! This example creates a `Point` struct that implements [`Add`] and [`Sub`], 40 //! and then demonstrates adding and subtracting two `Point`s. 41 //! 42 //! ```rust 43 //! use std::ops::{Add, Sub}; 44 //! 45 //! #[derive(Debug, Copy, Clone, PartialEq)] 46 //! struct Point { 47 //! x: i32, 48 //! y: i32, 49 //! } 50 //! 51 //! impl Add for Point { 52 //! type Output = Self; 53 //! 54 //! fn add(self, other: Self) -> Self { 55 //! Self {x: self.x + other.x, y: self.y + other.y} 56 //! } 57 //! } 58 //! 59 //! impl Sub for Point { 60 //! type Output = Self; 61 //! 62 //! fn sub(self, other: Self) -> Self { 63 //! Self {x: self.x - other.x, y: self.y - other.y} 64 //! } 65 //! } 66 //! 67 //! assert_eq!(Point {x: 3, y: 3}, Point {x: 1, y: 0} + Point {x: 2, y: 3}); 68 //! assert_eq!(Point {x: -1, y: -3}, Point {x: 1, y: 0} - Point {x: 2, y: 3}); 69 //! ``` 70 //! 71 //! See the documentation for each trait for an example implementation. 72 //! 73 //! The [`Fn`], [`FnMut`], and [`FnOnce`] traits are implemented by types that can be 74 //! invoked like functions. Note that [`Fn`] takes `&self`, [`FnMut`] takes `&mut 75 //! self` and [`FnOnce`] takes `self`. These correspond to the three kinds of 76 //! methods that can be invoked on an instance: call-by-reference, 77 //! call-by-mutable-reference, and call-by-value. The most common use of these 78 //! traits is to act as bounds to higher-level functions that take functions or 79 //! closures as arguments. 80 //! 81 //! Taking a [`Fn`] as a parameter: 82 //! 83 //! ```rust 84 //! fn call_with_one<F>(func: F) -> usize 85 //! where F: Fn(usize) -> usize 86 //! { 87 //! func(1) 88 //! } 89 //! 90 //! let double = |x| x * 2; 91 //! assert_eq!(call_with_one(double), 2); 92 //! ``` 93 //! 94 //! Taking a [`FnMut`] as a parameter: 95 //! 96 //! ```rust 97 //! fn do_twice<F>(mut func: F) 98 //! where F: FnMut() 99 //! { 100 //! func(); 101 //! func(); 102 //! } 103 //! 104 //! let mut x: usize = 1; 105 //! { 106 //! let add_two_to_x = || x += 2; 107 //! do_twice(add_two_to_x); 108 //! } 109 //! 110 //! assert_eq!(x, 5); 111 //! ``` 112 //! 113 //! Taking a [`FnOnce`] as a parameter: 114 //! 115 //! ```rust 116 //! fn consume_with_relish<F>(func: F) 117 //! where F: FnOnce() -> String 118 //! { 119 //! // `func` consumes its captured variables, so it cannot be run more 120 //! // than once 121 //! println!("Consumed: {}", func()); 122 //! 123 //! println!("Delicious!"); 124 //! 125 //! // Attempting to invoke `func()` again will throw a `use of moved 126 //! // value` error for `func` 127 //! } 128 //! 129 //! let x = String::from("x"); 130 //! let consume_and_return_x = move || x; 131 //! consume_with_relish(consume_and_return_x); 132 //! 133 //! // `consume_and_return_x` can no longer be invoked at this point 134 //! ``` 135 //! 136 //! [`clone`]: Clone::clone 137 //! [operator precedence]: ../../reference/expressions.html#expression-precedence 138 139 #![stable(feature = "rust1", since = "1.0.0")] 140 141 mod arith; 142 mod bit; 143 mod control_flow; 144 mod deref; 145 mod drop; 146 mod function; 147 mod generator; 148 mod index; 149 mod index_range; 150 mod range; 151 mod try_trait; 152 mod unsize; 153 154 #[stable(feature = "rust1", since = "1.0.0")] 155 pub use self::arith::{Add, Div, Mul, Neg, Rem, Sub}; 156 #[stable(feature = "op_assign_traits", since = "1.8.0")] 157 pub use self::arith::{AddAssign, DivAssign, MulAssign, RemAssign, SubAssign}; 158 159 #[stable(feature = "rust1", since = "1.0.0")] 160 pub use self::bit::{BitAnd, BitOr, BitXor, Not, Shl, Shr}; 161 #[stable(feature = "op_assign_traits", since = "1.8.0")] 162 pub use self::bit::{BitAndAssign, BitOrAssign, BitXorAssign, ShlAssign, ShrAssign}; 163 164 #[stable(feature = "rust1", since = "1.0.0")] 165 pub use self::deref::{Deref, DerefMut}; 166 167 #[unstable(feature = "receiver_trait", issue = "none")] 168 pub use self::deref::Receiver; 169 170 #[stable(feature = "rust1", since = "1.0.0")] 171 pub use self::drop::Drop; 172 173 #[stable(feature = "rust1", since = "1.0.0")] 174 pub use self::function::{Fn, FnMut, FnOnce}; 175 176 #[stable(feature = "rust1", since = "1.0.0")] 177 pub use self::index::{Index, IndexMut}; 178 179 #[stable(feature = "rust1", since = "1.0.0")] 180 pub use self::range::{Range, RangeFrom, RangeFull, RangeTo}; 181 182 pub(crate) use self::index_range::IndexRange; 183 184 #[stable(feature = "inclusive_range", since = "1.26.0")] 185 pub use self::range::{Bound, RangeBounds, RangeInclusive, RangeToInclusive}; 186 187 #[unstable(feature = "one_sided_range", issue = "69780")] 188 pub use self::range::OneSidedRange; 189 190 #[unstable(feature = "try_trait_v2", issue = "84277")] 191 pub use self::try_trait::{FromResidual, Try}; 192 193 #[unstable(feature = "try_trait_v2_yeet", issue = "96374")] 194 pub use self::try_trait::Yeet; 195 196 #[unstable(feature = "try_trait_v2_residual", issue = "91285")] 197 pub use self::try_trait::Residual; 198 199 pub(crate) use self::try_trait::{ChangeOutputType, NeverShortCircuit}; 200 201 #[unstable(feature = "generator_trait", issue = "43122")] 202 pub use self::generator::{Generator, GeneratorState}; 203 204 #[unstable(feature = "coerce_unsized", issue = "18598")] 205 pub use self::unsize::CoerceUnsized; 206 207 #[unstable(feature = "dispatch_from_dyn", issue = "none")] 208 pub use self::unsize::DispatchFromDyn; 209 210 #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")] 211 pub use self::control_flow::ControlFlow; 212