::unwind_safe

通过类似于try-finally的构建器模式实现可读的unwind-safe代码

let mut body_called = false;
let mut finally_called = false;

// Let's imagine some code being run in a context where
// panics do not affect us (`panic::catch_unwind`), or some
// executor running stuff on another thread…
let _ = ::crossbeam::thread::scope(|s| drop(s.spawn(|_| {

    let ft = {
        ::unwind_safe::with_state(())
            .try_eval(|_| {
                body_called = true;
                if ::rand::random() {
                    panic!();
                } else {
                    42
                }
            })
            .finally(|_| { // <- The point of this crate!
                finally_called = true;
            })
    };
    // This is only reached when `try_eval` does not panic, obviously.
    assert_eq!(ft, 42);

})));

// Whatever code path was taken, the finally block is always executed
// (that's the point of this crate!).
// From a place that survives the panic (if any), we thus observe:
assert!(body_called);
assert!(finally_called);

具有实际拥有的状态

如果析构函数需要访问 finally / 延迟块中的拥有的 State¹ (type State = …: 您选择的类型)，