rust 21 lines · 7 steps

Collecting Results in Rust iterators

Rust's iterators can gather fallible operations into a single Result, short-circuiting on the first error.

Explained by highlit

Intermediate iterators error-handling result parsing functional

1use std::num::ParseIntError;
2 
3fn parse_line(line: &str) -> Result<Vec<i64>, ParseIntError> {
4    line.split(',')
5        .map(str::trim)
6        .filter(|token| !token.is_empty())
7        .map(|token| token.parse::<i64>())
8        .collect()
9}
10 
11fn sum_all_lines(input: &str) -> Result<i64, ParseIntError> {
12    let numbers: Vec<i64> = input
13        .lines()
14        .map(parse_line)
15        .collect::<Result<Vec<_>, _>>()?
16        .into_iter()
17        .flatten()
18        .collect();
19 
20    Ok(numbers.iter().sum())
21}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Collecting an iterator of `Result` items into `Result<Vec<_>, _>` stops at the first error and returns it.
2The `?` operator unwraps a successful collection or propagates the parse error up the call stack.
3Chaining `map`, `filter`, and `flatten` keeps transformation logic declarative and free of manual loops.

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