// Protocol dispatch on `List(Protocol)` items where the list pointer is
// passed into another function — verifies the boxed payload survives an
// extra call frame between erasure and dispatch.

#import "modules/std.sx";

Sizable :: protocol {
    size :: () -> i64;
}

Leaf :: struct { value: i64; }
impl Sizable for Leaf {
    size :: (self: *Leaf) -> i64 { self.value }
}

add :: (items: *List(Sizable), w: Leaf) {
    p := w;
    items.append(p);
}

dispatch_fn :: (items: *List(Sizable)) {
    out("dispatch_fn: about to dispatch\n");
    s := items.items[0].size();
    print("dispatch_fn: result = {}\n", s);
}

main :: () -> void {
    items : List(Sizable) = .{};
    add(@items, Leaf.{ value = 42 });

    // Direct dispatch twice
    out("=== Direct 1 ===\n");
    r1 := items.items[0].size();
    print("r1 = {}\n", r1);

    out("=== Direct 2 ===\n");
    r2 := items.items[0].size();
    print("r2 = {}\n", r2);

    // Then from function
    out("=== From function ===\n");
    dispatch_fn(@items);
    out("=== OK ===\n");
}