Expand description
Implement some functionality for a type.
The impl
keyword is primarily used to define implementations on types. Inherent
implementations are standalone, while trait implementations are used to implement traits for
types, or other traits.
Functions and consts can both be defined in an implementation. A function defined in an
impl
block can be standalone, meaning it would be called like Foo::bar()
. If the function
takes self
, &self
, or &mut self
as its first argument, it can also be called using
method-call syntax, a familiar feature to any object oriented programmer, like foo.bar()
.
struct Example {
number: i32,
}
impl Example {
fn boo() {
println!("boo! Example::boo() was called!");
}
fn answer(&mut self) {
self.number += 42;
}
fn get_number(&self) -> i32 {
self.number
}
}
trait Thingy {
fn do_thingy(&self);
}
impl Thingy for Example {
fn do_thingy(&self) {
println!("doing a thing! also, number is {}!", self.number);
}
}
RunFor more information on implementations, see the Rust book or the Reference.
The other use of the impl
keyword is in impl Trait
syntax, which can be seen as a shorthand
for “a concrete type that implements this trait”. Its primary use is working with closures,
which have type definitions generated at compile time that can’t be simply typed out.
fn thing_returning_closure() -> impl Fn(i32) -> bool {
println!("here's a closure for you!");
|x: i32| x % 3 == 0
}
RunFor more information on impl Trait
syntax, see the Rust book.