use std::cmp::Ordering;

struct MyStruct {
    a: usize,
    b: String,
    c: String,
    d: usize,
}

enum MyStructKey {
    A,
    B,
    C,
    D,
}

impl MyStruct {
    fn cmp_by(&self, other: &Self, keys: &[MyStructKey]) -> Ordering {
        match keys.split_first() {
            Some((MyStructKey::A, tail)) => {
                self.a.cmp(&other.a).then_with(|| self.cmp_by(other, tail))
            }
            Some((MyStructKey::B, tail)) => {
                self.b.cmp(&other.b).then_with(|| self.cmp_by(other, tail))
            }
            Some((MyStructKey::C, tail)) => {
                self.c.cmp(&other.c).then_with(|| self.cmp_by(other, tail))
            }
            Some((MyStructKey::D, tail)) => {
                self.d.cmp(&other.d).then_with(|| self.cmp_by(other, tail))
            }
            None => Ordering::Equal,
        }
    }
}

fn main() {
    let a = MyStruct {
        a: 42,
        b: "foo".into(),
        c: "bar".into(),
        d: 314,
    };

    let b = MyStruct {
        a: 271428,
        b: "aaaa".into(),
        c: "bbbb".into(),
        d: 0,
    };

    println!("{:?}", a.cmp_by(&b, &[MyStructKey::A]));
    println!("{:?}", a.cmp_by(&b, &[MyStructKey::B]));

    println!("{:?}", b.cmp_by(&a, &[MyStructKey::A]));
    println!("{:?}", b.cmp_by(&a, &[MyStructKey::B]));

    println!("{:?}", a.cmp_by(&b, &[MyStructKey::A, MyStructKey::B]));
    println!("{:?}", a.cmp_by(&b, &[MyStructKey::B, MyStructKey::A]));

    println!("{:?}", a.cmp_by(&b, &[MyStructKey::B, MyStructKey::A, MyStructKey::C, MyStructKey::D]));
}