Operator Overloading
In Rust, many of the operators can be overloaded via traits. That is, some operators can
be used to accomplish different tasks based on their input arguments. This is possible
because operators are syntactic sugar for method calls. For example, the +
operator in
a + b
calls the add
method (as in a.add(b)
). This add
method is part of the Add
trait. Hence, the +
operator can be used by any implementor of the Add
trait.
A list of the traits, such as Add
, that overload operators can be found in core::ops
.
use std::ops; struct Foo; struct Bar; #[derive(Debug)] struct FooBar; #[derive(Debug)] struct BarFoo; // The `std::ops::Add` trait is used to specify the functionality of `+`. // Here, we make `Add<Bar>` - the trait for addition with a RHS of type `Bar`. // The following block implements the operation: Foo + Bar = FooBar impl ops::Add<Bar> for Foo { type Output = FooBar; fn add(self, _rhs: Bar) -> FooBar { println!("> Foo.add(Bar) was called"); FooBar } } // By reversing the types, we end up implementing non-commutative addition. // Here, we make `Add<Foo>` - the trait for addition with a RHS of type `Foo`. // This block implements the operation: Bar + Foo = BarFoo impl ops::Add<Foo> for Bar { type Output = BarFoo; fn add(self, _rhs: Foo) -> BarFoo { println!("> Bar.add(Foo) was called"); BarFoo } } fn main() { println!("Foo + Bar = {:?}", Foo + Bar); println!("Bar + Foo = {:?}", Bar + Foo); }