defer.rs

macro_rules! defer {
    ($f:expr) => {
        let __defer = {
            struct Defer<F: FnMut()>(F);
            impl<F: FnMut()> Drop for Defer<F> {
                fn drop(&mut self) {
                    (self.0)();
                }
            }
            Defer($f)
        };
    };
}