src/test/ui/self/uniq-self-in-mut-slot.rs

// run-pass
#![feature(box_syntax)]

struct X {
    a: isize
}

trait Changer {
    fn change(self: Box<Self>) -> Box<Self>;
}

impl Changer for X {
    fn change(mut self: Box<X>) -> Box<X> {
        self.a = 55;
        self
    }
}

pub fn main() {
    let x: Box<_> = box X { a: 32 };
    let new_x = x.change();
    assert_eq!(new_x.a, 55);
}