// Feature 1 — pack spread into a call's positional arguments. `f(..xs.get)`
// projects `get` over the pack and spreads the resulting tuple into f's params:
//   add2(..xs.get)  ≈  add2(xs[0].get(), xs[1].get())
// The canonical's `mapper(..sources.value)` is this shape.

#import "modules/std.sx";

Box :: protocol(T: Type) {
    get :: () -> s64;
}
IntCell :: struct { v: s64; }
Dbl :: struct { n: s64; }
impl Box(s64) for IntCell { get :: (self: *IntCell) -> s64 => self.v; }
impl Box(s64) for Dbl { get :: (self: *Dbl) -> s64 => self.n * 2; }

add2 :: (a: s64, b: s64) -> s64 { return a + b; }
add3 :: (a: s64, b: s64, c: s64) -> s64 { return a + b + c; }

via2 :: (..xs: Box) -> s64 { return add2(..xs.get); }
via3 :: (..xs: Box) -> s64 { return add3(..xs.get); }

main :: () -> s32 {
    print("two={}\n", via2(IntCell.{ v = 10 }, Dbl.{ n = 5 }));            // 10 + 10 = 20
    print("three={}\n", via3(Dbl.{ n = 1 }, IntCell.{ v = 2 }, Dbl.{ n = 3 })); // 2 + 2 + 6 = 10
    0
}