A basic kind of callback macro

callback.rs

///
/// A generic version of `callback macro`
///
/// # Example
/// ```rust
/// #[macro_use(callback)]
/// # extern crate framework;
/// trait Command {
///     fn run(&self) {}
/// }
/// struct Test { x: i32 }
/// impl Test {
///     fn new() -> Test { Test{ x: 42} }
/// }
/// impl Command for Test {
///     fn run(&self) { println!("{:?}", self.x); }
/// }
/// fn main() {
///     let mut t = Test::new();
///     let macro_test = callback!(Command::run);
///     println!("{:?}", macro_test(&mut t as &mut Command) )
/// }
/// ```
#[macro_export]
macro_rules! callback {
    ($t:ident :: $m:ident) => {{
        fn __f(x: &mut $t) { x.$m() }
        __f
    }}
}