Implementing defer in Rust

gistfile1.rs

struct Deferrer
{
    df : ~fn()
}

impl Drop for Deferrer
{
    fn finalize(&self)
    {
        (self.df)();
    }
}

fn defer(df : ~fn()) -> Deferrer
{
    return Deferrer{df : df};
}

fn main()
{
    let some_var = 1;
    let _a = defer(|| {io::println(fmt!("Destroying %d", some_var))});
    io::println(fmt!("Using %d", some_var));
}