// Feature 1 — heterogeneous protocol-constrained variadic pack (binding).
//
// `..xs: Show` (no `[]`, no `$`) is a pack, not a slice: each call site
// monomorphizes with the concrete per-position arg types (Decision 1 — a pack
// is a comptime mechanism, no runtime pack value), and `xs.len` is a comptime
// constant. Arity and element types vary per call; each call is a distinct
// specialization.
//
// DESIGN (locked): a pack element is viewed THROUGH the protocol — only the
// protocol's own interface (its methods, and the projections `xs.T` / `xs.value`)
// is accessible, NOT arbitrary concrete members. So `xs[i].get()` / `xs.T` are
// the intended interface; `xs[i].v` (a field on the concrete IntBox, not part
// of `Show`) is an error. Those are still being implemented — this example
// locks in only the binding + comptime `xs.len`, the protocol-agnostic part.

#import "modules/std.sx";

Show :: protocol(T: Type) {
    get :: (self: *Self) -> T;
}

IntBox :: struct { v: s64; }
StrBox :: struct { s: string; }
impl Show(s64) for IntBox { get :: (self: *IntBox) -> s64 => self.v; }
impl Show(string) for StrBox { get :: (self: *StrBox) -> string => self.s; }

howmany :: (..xs: Show) -> s64 {
    return xs.len;
}

main :: () -> s32 {
    a := IntBox.{ v = 42 };
    b := IntBox.{ v = 7 };
    c := StrBox.{ s = "cool" };
    print("n0={}\n", howmany());            // empty pack
    print("n2={}\n", howmany(a, b));         // two elements
    print("n3={}\n", howmany(a, b, c));      // heterogeneous: IntBox, IntBox, StrBox
    0;
}
