continuwuity/src/core/utils/defer.rs

#[macro_export]
macro_rules! defer {
	($body:block) => {
		struct _Defer_<F: FnMut()> {
			closure: F,
		}

		impl<F: FnMut()> Drop for _Defer_<F> {
			fn drop(&mut self) { (self.closure)(); }
		}

		let _defer_ = _Defer_ { closure: || $body };
	};

	($body:expr_2021) => {
		$crate::defer! {{ $body }}
	};
}

#[macro_export]
macro_rules! scope_restore {
	($val:ident, $ours:expr_2021) => {
		let theirs = $crate::utils::exchange($val, $ours);
		$crate::defer! {{ *$val = theirs; }};
	};
}