// Feature 1 — protocol-interface method calls on heterogeneous pack elements.
//
// `..xs: Greeter` binds per call shape; each `xs[i]` is the concrete element,
// and calling the protocol's own method `greet()` on it dispatches to that
// element's impl. Elements may be DIFFERENT concrete types (Dog, Cat) as long
// as each conforms to Greeter — this is the protocol-interface access the
// pack is for. (Protocol method decls omit the implicit `self`; impls list it.)

#import "modules/std.sx";

Greeter :: protocol {
    greet :: () -> s64;
}

Dog :: struct { age: s64; }
Cat :: struct { lives: s64; }
impl Greeter for Dog { greet :: (self: *Dog) -> s64 => self.age; }
impl Greeter for Cat { greet :: (self: *Cat) -> s64 => self.lives * 100; }

pair_sum :: (..xs: Greeter) -> s64 {
    return xs[0].greet() + xs[1].greet();
}

main :: () -> s32 {
    d := Dog.{ age = 3 };
    c := Cat.{ lives = 9 };
    print("dog+cat={}\n", pair_sum(d, c));   // 3 + 900 = 903 (heterogeneous)
    print("cat+dog={}\n", pair_sum(c, d));   // 900 + 3 = 903 (order swapped)
    print("dog+dog={}\n", pair_sum(d, Dog.{ age = 4 })); // 3 + 4 = 7
    0;
}