Rust by Example

Early returns

In the previous example, we explicitly handled the errors using combinators. Another way to deal with this case analysis is to use a combination of match statements and early returns.

That is, we can simply stop executing the function and return the error if one occurs. For some, this form of code can be easier to both read and write. Consider this version of the previous example, rewritten using early returns:

use std::num::ParseIntError;

fn multiply(first_number_str: &str, second_number_str: &str) -> Result {

let first_number = match first_number_str.parse::() {

Ok(first_number)  => first_number,

Err(e) => return Err(e),

};

let second_number = match second_number_str.parse::() {

Ok(second_number)  => second_number,

Err(e) => return Err(e),

};

Ok(first_number * second_number)

}

fn print(result: Result) {

match result {

Ok(n)  => println!("n is {}", n),

Err(e) => println!("Error: {}", e),

}

}

fn main() {

print(multiply("10", "2"));

print(multiply("t", "2"));

}

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At this point, we've learned to explicitly handle errors using combinators and early returns. While we generally want to avoid panicking, explicitly handling all of our errors is cumbersome.

In the next section, we'll introduce ? for the cases where we simply need to unwrap without possibly inducing panic.