The BitOr trait is used to specify the functionality of |.

Example

A trivial implementation of BitOr. When Foo | Foo happens, it ends up calling bitor, and therefore, main prints Bitwise Or-ing!.

struct Foo;

impl BitOr<Foo, Foo> for Foo {
    fn bitor(&self, _rhs: &Foo) -> Foo {
        println!("Bitwise Or-ing!");
        *self
    }
}

fn main() {
    Foo | Foo;
}