How to manually return a Result<(), Box>?

Question

I want to return an error from a function in case a condition is true:

use std::error::Error;

pub fn run() -> Result<(), Box> {
    //         


        

Answer 1

A Result is an enum with two variants. To return either of them, you just use corresponding variants.

fn foo(var: bool) -> Result<(), i32> {
    if var {
        Ok(()) //in fact this is std::result::Result::Ok
    } else {
        Err(-3) //in fact this is std::result::Result::Err
    }
}

The reason why you don't have to write std::result::Result::Ok is that it is in the prelude. As you can see, you don't have to stick to Box, but can return any type you want. It is a generic enum, with no restrictions.

The ?-operator is a handy shortcut for early returns, so you don't have to be too verbose about results.