defer

lib.rs

fn defer<F: FnOnce()>(f: F) -> impl Drop {
    struct D<F: FnOnce()>(Option<F>);
    impl<F: FnOnce()> Drop for D<F> {
        fn drop(&mut self) {
            if let Some(f) = self.0.take() {
                f()
            }
        }
    }
    D(Some(f))
}