# Module core::ops 1.0.0[−][src]

Overloadable operators.

Implementing these traits allows you to overload certain operators.

Some of these traits are imported by the prelude, so they are available in every Rust program. Only operators backed by traits can be overloaded. For example, the addition operator (`+`) can be overloaded through the `Add` trait, but since the assignment operator (`=`) has no backing trait, there is no way of overloading its semantics. Additionally, this module does not provide any mechanism to create new operators. If traitless overloading or custom operators are required, you should look toward macros or compiler plugins to extend Rust’s syntax.

Implementations of operator traits should be unsurprising in their respective contexts, keeping in mind their usual meanings and operator precedence. For example, when implementing `Mul`, the operation should have some resemblance to multiplication (and share expected properties like associativity).

Note that the `&&` and `||` operators short-circuit, i.e., they only evaluate their second operand if it contributes to the result. Since this behavior is not enforceable by traits, `&&` and `||` are not supported as overloadable operators.

Many of the operators take their operands by value. In non-generic contexts involving built-in types, this is usually not a problem. However, using these operators in generic code, requires some attention if values have to be reused as opposed to letting the operators consume them. One option is to occasionally use `clone`. Another option is to rely on the types involved providing additional operator implementations for references. For example, for a user-defined type `T` which is supposed to support addition, it is probably a good idea to have both `T` and `&T` implement the traits `Add<T>` and `Add<&T>` so that generic code can be written without unnecessary cloning.

# Examples

This example creates a `Point` struct that implements `Add` and `Sub`, and then demonstrates adding and subtracting two `Point`s.

    use std::ops::{Add, Sub};

    #[derive(Debug, Copy, Clone, PartialEq)]
    struct Point {
        x: i32,
        y: i32,
    }

    impl Add for Point {
        type Output = Self;

        fn add(self, other: Self) -> Self {
            Self {x: self.x + other.x, y: self.y + other.y}
        }
    }

    impl Sub for Point {
        type Output = Self;

        fn sub(self, other: Self) -> Self {
            Self {x: self.x - other.x, y: self.y - other.y}
        }
    }

    assert_eq!(Point {x: 3, y: 3}, Point {x: 1, y: 0} + Point {x: 2, y: 3});
    assert_eq!(Point {x: -1, y: -3}, Point {x: 1, y: 0} - Point {x: 2, y: 3});

Run

See the documentation for each trait for an example implementation.

The `Fn`, `FnMut`, and `FnOnce` traits are implemented by types that can be invoked like functions. Note that `Fn` takes `&self`, `FnMut` takes `&mut self` and `FnOnce` takes `self`. These correspond to the three kinds of methods that can be invoked on an instance: call-by-reference, call-by-mutable-reference, and call-by-value. The most common use of these traits is to act as bounds to higher-level functions that take functions or closures as arguments.

Taking a `Fn` as a parameter:

    fn call_with_one<F>(func: F) -> usize
        where F: Fn(usize) -> usize
    {
        func(1)
    }

    let double = |x| x * 2;
    assert_eq!(call_with_one(double), 2);

Run

Taking a `FnMut` as a parameter:

    fn do_twice<F>(mut func: F)
        where F: FnMut()
    {
        func();
        func();
    }

    let mut x: usize = 1;
    {
        let add_two_to_x = || x += 2;
        do_twice(add_two_to_x);
    }

    assert_eq!(x, 5);

Run

Taking a `FnOnce` as a parameter:

    fn consume_with_relish<F>(func: F)
        where F: FnOnce() -> String
    {
        // `func` consumes its captured variables, so it cannot be run more
        // than once
        println!("Consumed: {}", func());

        println!("Delicious!");

        // Attempting to invoke `func()` again will throw a `use of moved
        // value` error for `func`
    }

    let x = String::from("x");
    let consume_and_return_x = move || x;
    consume_with_relish(consume_and_return_x);

    // `consume_and_return_x` can no longer be invoked at this point

Run

## Structs

Range | A (half-open) range bounded inclusively below and exclusively above (`start..end`).
RangeFrom | A range only bounded inclusively below (`start..`).
RangeFull | An unbounded range (`..`).
RangeInclusive | A range bounded inclusively below and above (`start..=end`).
RangeTo | A range only bounded exclusively above (`..end`).
RangeToInclusive | A range only bounded inclusively above (`..=end`).

## Enums

ControlFlow | Experimental Used to tell an operation whether it should exit early or go on as usual.
GeneratorState | Experimental The result of a generator resumption.
Bound | An endpoint of a range of keys.

## Traits

CoerceUnsized | Experimental Trait that indicates that this is a pointer or a wrapper for one, where unsizing can be performed on the pointee.
DispatchFromDyn | Experimental This is used for object safety, to check that a method’s receiver type can be dispatched on.
Generator | Experimental The trait implemented by builtin generator types.
Try | Experimental A trait for customizing the behavior of the `?` operator.
Add | The addition operator `+`.
AddAssign | The addition assignment operator `+=`.
BitAnd | The bitwise AND operator `&`.
BitAndAssign | The bitwise AND assignment operator `&=`.
BitOr | The bitwise OR operator `|`.
BitOrAssign | The bitwise OR assignment operator `|=`.
BitXor | The bitwise XOR operator `^`.
BitXorAssign | The bitwise XOR assignment operator `^=`.
Deref | Used for immutable dereferencing operations, like `*v`.
DerefMut | Used for mutable dereferencing operations, like in `*v = 1;`.
Div | The division operator `/`.
DivAssign | The division assignment operator `/=`.
Drop | Custom code within the destructor.
Fn | The version of the call operator that takes an immutable receiver.
FnMut | The version of the call operator that takes a mutable receiver.
FnOnce | The version of the call operator that takes a by-value receiver.
Index | Used for indexing operations (`container[index]`) in immutable contexts.
IndexMut | Used for indexing operations (`container[index]`) in mutable contexts.
Mul | The multiplication operator `*`.
MulAssign | The multiplication assignment operator `*=`.
Neg | The unary negation operator `-`.
Not | The unary logical negation operator `!`.
RangeBounds | `RangeBounds` is implemented by Rust’s built-in range types, produced by range syntax like `..`, `a..`, `..b`, `..=c`, `d..e`, or `f..=g`.
Rem | The remainder operator `%`.
RemAssign | The remainder assignment operator `%=`.
Shl | The left shift operator `<<`. Note that because this trait is implemented for all integer types with multiple right-hand-side types, Rust’s type checker has special handling for `_ << _`, setting the result type for integer operations to the type of the left-hand-side operand. This means that though `a << b` and `a.shl(b)` are one and the same from an evaluation standpoint, they are different when it comes to type inference.
ShlAssign | The left shift assignment operator `<<=`.
Shr | The right shift operator `>>`. Note that because this trait is implemented for all integer types with multiple right-hand-side types, Rust’s type checker has special handling for `_ >> _`, setting the result type for integer operations to the type of the left-hand-side operand. This means that though `a >> b` and `a.shr(b)` are one and the same from an evaluation standpoint, they are different when it comes to type inference.
ShrAssign | The right shift assignment operator `>>=`.
Sub | The subtraction operator `-`.
SubAssign | The subtraction assignment operator `-=`.