Attribute Macro solution 

#[solution]

A solution of an advent of code problem.

You need to pass in day = X for the macro to work. If the function is named part1 or part2, the part gets set accordingly; otherwise you need to specify it as part = Y.

You can also specify the expected result of the example given in the puzzle using example = Z or example = [A, B, C, ...] if there are multiple. The examples need to be defined somewhere using elvish::example!() for them to work.

At the end of the day, this macro is mostly to reduce boilerplate but it’s easily expandable by hand.

Example usage

Solution for day 1 of 2023:

#[elvish::solution(day = 1, example = 142)]
fn part1(input: &str) -> u32 {
    input
        .lines()
        .filter(|line| !line.is_empty())
        .map(|line| {
            let mut iter = line.chars().filter_map(|c| c.to_digit(10));
 
            let a = iter.next().unwrap();
            let b = iter.last().unwrap_or(a);
 
            a * 10 + b
        })
        .sum()
}

which generates:

impl elvish::solution::Part<1, 1> for crate::Solutions {
    fn solve(input: &str) -> impl std::fmt::Display {
        part1(input)
    }
}
 
#[test]
fn part1_example() {
    assert_eq!(part1(EXAMPLE_PART1), 142)
}

fn part1(input: &str) -> u32 {
// --snip--
}