How do you unwrap a Result on Ok or return from the function on Err?

Question

I have a function that calls another function which returns a Result. I need to check if the Result is Ok or Err and if it is an Err, I need to return early from my function. This is what I'm doing now:

match callable(&mut param) {
    Ok(_v) => (),
    Err(_e) => return,
};

Is there a more idiomatic Rust way to do this?

Answer 1

You can create a macro:

macro_rules! unwrap_or_return {
    ( $e:expr ) => {
        match $e {
            Ok(x) => x,
            Err(_) => return,
        }
    }
}

fn callable(param: &mut i32) -> Result<i32, ()> {
    Ok(*param)
}

fn main() {
    let mut param = 0;
    let res = unwrap_or_return!(callable(&mut param));

    println!("{:?}", res);
}

Note that I wouldn't recommend discarding the errors. Rust's error handling is pretty ergonomic, so I would return the error, even if it is only to log it:

fn callable(param: &mut i32) -> Result<i32, ()> {
    Ok(*param)
}

fn run() -> Result<(), ()> {
    let mut param = 0;
    let res = callable(&mut param)?;

    println!("{:?}", res);

    Ok(())
}

fn main() {
    if let Err(()) = run() {
        println!("Oops, something went wrong!");
    }
}

Answer 2

You can use my unwrap_or crate to accomplish this.

You can do:

unwrap_or_ok!(callable(&mut param), _, return);

And if you want the result and to return the error, you can do:

let v = unwrap_or_ok!(callable(&mut param), error, return error);