Day 2 (Advent of Code 2022)

[abderrahimAMZ]

hi fasterthanlime, big fan here! i check your AoC answers to learn from them, i like how you solve them and the explaining is clear. however, i don't get why exactly why not just build the logic directly instead of implementing enums and structs. if you already have a blog, youtube video, explaining the thing, give me the link and don't waste your time.

[fasterthanlime]

however, i don't get why exactly why not just build the logic directly instead of implementing enums and structs

So there's several reasons!

One reason to use types is so you remember what a thing is for. Let's say for example you have:

struct Person {
  first_name: String,
  last_name: String,
}

You can accidentally do something like:

person_a.last_name = person_b.first_name;

If instead you used types like:

struct Person {
  first_name: FirstName,
  last_name: LastName,
}

Then the compiler would've caught that. This code for example:

struct FirstName(String);
struct LastName(String);

struct Person {
    first_name: FirstName,
    last_name: LastName,
}

fn main() {
    let person1 = Person {
        first_name: FirstName("John".into()),
        last_name: LastName("Doe".into()),
    };

    let person2 = Person {
        first_name: FirstName("Jane".into()),
        last_name: LastName("Doe".into()),
    };

    person1.last_name = person2.first_name;

    println!("Hello, world!");
}

Gives us this error:

$ cargo c
    Checking whytypes v0.1.0 (/Users/amos/bearcove/whytypes)
error[E0308]: mismatched types
  --> src/main.rs:20:25
   |
20 |     person1.last_name = person2.first_name;
   |     -----------------   ^^^^^^^^^^^^^^^^^^ expected `LastName`, found `FirstName`
   |     |
   |     expected due to the type of this binding

This is a pretty contrived example, of course. But for example, I'd rather receive one of these:

struct Point3 {
  x: f64,
  y: f64,
  z: f64,
}

Than a (f64, f64, f64) or a [f64; 3].

---

Of course you wouldn't necessarily have to go through intermediate types like I do, but for me it's just how i think about problems. Once you find the right data structure, solving the problem itself becomes trivial.