static struct Asteroid { uint size; }
static struct Spaceship { uint size; }
alias SpaceObject = Variant!(Asteroid, Spaceship);

alias collideWith = match!(
    (Asteroid x, Asteroid y) => "a/a",
    (Asteroid x, Spaceship y) => "a/s",
    (Spaceship x, Asteroid y) => "s/a",
    (Spaceship x, Spaceship y) => "s/s",
);

import mir.utility: min;

// Direct access of a member in case of all algebraic types has this member
alias oops = (a, b) => (a.size + b.size) > 3 && min(a.size, b.size) > 1;

alias collide = (x, y) => oops(x, y) ? "big-boom" : collideWith(x, y);

auto ea = Asteroid(1);
auto es = Spaceship(2);
auto oa = SpaceObject(ea);
auto os = SpaceObject(es);

// Asteroid-Asteroid
assert(collide(ea, ea) == "a/a");
assert(collide(ea, oa) == "a/a");
assert(collide(oa, ea) == "a/a");
assert(collide(oa, oa) == "a/a");

// Asteroid-Spaceship
assert(collide(ea, es) == "a/s");
assert(collide(ea, os) == "a/s");
assert(collide(oa, es) == "a/s");
assert(collide(oa, os) == "a/s");

// Spaceship-Asteroid
assert(collide(es, ea) == "s/a");
assert(collide(es, oa) == "s/a");
assert(collide(os, ea) == "s/a");
assert(collide(os, oa) == "s/a");

// Spaceship-Spaceship
assert(collide(es, es) == "big-boom");
assert(collide(es, os) == "big-boom");
assert(collide(os, es) == "big-boom");
assert(collide(os, os) == "big-boom");