iOS lock step keyboard + metal

library/modules/std.sx

@@ -329,6 +329,15 @@ print :: ($fmt: string, args: ..Any) {
     #insert "out(result);";
 }
 
+// User-space `xx` extension. `xx val : T` where the built-in conversion
+// ladder makes no progress falls through to an `impl Into(T) for Source`
+// lookup; the compiler monomorphises `convert` for the (Source, T) pair
+// and emits a direct call. Compile-time only — no vtable, no runtime
+// dispatch.
+Into :: protocol(Target: Type) {
+    convert :: () -> Target;
+}
+
 List :: struct ($T: Type) {
     items: [*]T = null;
     len: s64 = 0;