struct finish<T: Copy> {
  arg: {val: T, fin: extern fn(T)},
  drop { self.arg.fin(self.arg.val); }
}

fn finish<T: Copy>(arg: {val: T, fin: extern fn(T)}) -> finish<T> {
    finish {
        arg: arg
    }
}

fn main() {
    let box = @mut 10;
    fn dec_box(&&i: @mut int) { *i -= 1; }

    { let _i <- finish({val: box, fin: dec_box}); }
    assert (*box == 9);
}