Learning Rust via Advent of Code

Re:Learning Rust via Advent of Code by WakiMiko on Monday February 04, 2019 @01:58PM (#19079436)

For sorting sequential fields you can chain comparisons with .then():

    struct Date {
        year: u32,
        month: u32,
        day: u32,
    }
    
    let mut vec: Vec<Date> = Vec::new();
    
    vec.sort_by(|a,b| {
       a.year.cmp(&b.year)
        .then(a.month.cmp(&b.month))
        .then(a.day.cmp(&b.day))
    });

Alternatively you can derive PartialEq, PartialOrd, Eq and Ord for your struct, which will produce a lexicographic ordering based on the top-to-bottom declaration order of the struct's members:

    #[derive(PartialEq, PartialOrd, Eq, Ord)]
    struct Date {
        year: u32,
        month: u32,
        day: u32,
    }

[ Parent | on HN ]

Re:Learning Rust via Advent of Code by masklinn on Monday February 04, 2019 @03:07PM (#19080115)

Or you can use sort_by_key and extract the relevant sorting key as a tuple (or any other Ord structure) e.g.

    vec.sort_by_key(|d| (d.year, d.month, d.day))

sort_by is more flexible as it works fine with borrows, but when sorting on a series of integer values or references sort_by_key is great.

> Alternatively you can derive PartialCmp for your struct, which will produce a lexicographic ordering based on the top-to-bottom declaration order of the struct's members:

Do you mean PartialOrd? partial_cmp is the method. And `sort` requires absolute ordering (Ord) not just partial.

[ Parent | on HN ]

Re:Learning Rust via Advent of Code by WakiMiko on Monday February 04, 2019 @03:55PM (#19080542)

I quite like this tuple approach.

And yeah, I meant Ord (and the required other Traits), I edited my post. Thanks for pointing this out.

[ Parent | on HN ]