The ? operator

Calling several fallible functions with match gets noisy. The ? operator shortens it: placed after a Result, it gives you the Ok value, or returns the Err from the current function right away.

use std::num::ParseIntError;

fn double_text(s: &str) -> Result<i32, ParseIntError> {
    let n: i32 = s.trim().parse()?; // early return on error
    Ok(n * 2)
}

? only works in a function whose return type is a compatible Result. Here "abc".parse::<i32>() fails with a ParseIntError, and that same error type is what double_text returns.

Your task

Everything must be pub, because the tests use your crate as lesson. Use ? rather than match.

1. pub fn add_texts(a: &str, b: &str) -> Result<i32, std::num::ParseIntError> parses both strings as i32 and returns their sum.
2. pub fn sum_all(items: &[&str]) -> Result<i32, std::num::ParseIntError> parses every item and returns the total. It stops at the first bad item and returns that error. An empty slice gives Ok(0).