unwrap_or_terminate?

help
1 
    fn main() {
        a();
    }
    fn a() {

        let x = c().unwrap();
        b(x);
    }
    fn b(n: u8) {
        println!("{}", n);
    }
    fn c() -> Option<u8> {
        None
    }

Hi，the above code will panic because called Option::unwrap() on a None value' (c().unwrap()),the way to avoid it is to change to unwrap_or or unwrap_or_else,to use them, you have to provide a default value,but I just want immediately to stop the execution of the function if the c() is None。A good way to do that maybe the pattern matching.

    let x = match c() {
        Some(v) => v,
        None => {
            return;
        }
    };

is possible have a method like:

	let stop_the_fn=||{
		println("Stop Immediately")
	};
    let x = c().unwrap_or_terminate(stop_the_fn);
2

A method on Option won't be able to force the function that called it to return; that's just not how things work.

There's crates out there that provide a version of try!() for options which return None if the value passed to them is None, but it looks like you just want to return nothing. You can make your own macro for this in a few lines:

macro_rules! unwrap_or_ret (
    ($opt:expr) => (
        match $opt {
            Some(val) => val,
            None => return,
        }
    )
);

You can add an additional rule to run some code before returning:

macro_rules! unwrap_or_ret (
    ($opt:expr) => (
        match $opt {
            Some(val) => val,
            None => return,
        }
    );
    ($opt:expr, $before_ret: expr) => (
        match $opt {
            Some(val) => val,
            None => {
            // Silence "unused value" warnings
            let _ = $before_ret;
            return;
        }
    );
);

Usage:

let x = c();

let val = unwrap_or_ret!(x);
// or
let val = unwrap_or_ret!(x, println!("Stop immediately!"));
// or (blocks are expressions, so this works
let val = unwrap_or_ret(x, {
    println!("Stop immediately!");
    println!("Value was None.");
});
1 Like
3

:slightly_smiling: Thanks

4

Alternatively you can use Result instead of Option. That allows you to use the try! macro

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5