struct MyStruct{
    x: i32
}

impl MyStruct{
    pub fn foo(&mut self){
        self.x = 5;
    }
}

trait Foo {
    fn foo_foo( &mut self )
    {
        self.foo();
    }
}

impl Foo for MyStruct{
}

fn main() {
    println!("Hello, world!");
}