// Comptime reflection: `field_type($T, i) -> Type` — the type-only field
// projection the value-level reflection (`field_value` / `type_of`) couldn't
// express.
// Reflect a struct's fields by name (`field_name`) AND by type (`field_type`),
// and a tagged-union's variant payloads. It folds at lower time, so it composes
// inside `type_eq` / `type_name` / any type-arg slot.
#import "modules/std.sx";
#import "modules/std/meta.sx";

Point :: struct { x: i64; y: f64; on: bool; }

Msg :: enum { num: i64; tag: bool; quit; }

main :: () -> i32 {
    // Struct fields: name + type, position by position.
    print("Point has {} fields\n", field_count(Point));
    print("  0: {} : {}\n", field_name(Point, 0), type_name(field_type(Point, 0)));
    print("  1: {} : {}\n", field_name(Point, 1), type_name(field_type(Point, 1)));
    print("  2: {} : {}\n", field_name(Point, 2), type_name(field_type(Point, 2)));

    // field_type composes in a type-arg slot (type_eq folds at comptime).
    print("field 0 is i64: {}\n", type_eq(field_type(Point, 0), i64));
    print("field 1 is f64: {}\n", type_eq(field_type(Point, 1), f64));

    // Tagged-union variant payloads (the tagless `quit` → void).
    print("Msg.num  payload: {}\n", type_name(field_type(Msg, 0)));
    print("Msg.tag  payload: {}\n", type_name(field_type(Msg, 1)));
    print("Msg.quit payload: {}\n", type_name(field_type(Msg, 2)));
    return 0;
}
