Each control may only need one event, so combine them all into a single channel whose use depends on the sysData itself. Also we won't need to save the parentWindow anymore, as the change to the make() function will take care of that for us.

stdwndclass_windows.go

@@ -45,8 +45,8 @@ func stdWndProc(s *sysData) func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam
 			// TODO
 			return 0
 		case _WM_CLOSE:
-			if sysData.closing != nil {
-				sysData.closing <- struct{}{}
+			if s.event != nil {
+				s.event <- struct{}{}
 			}
 			return 0
 		default:

sysdata.go

@@ -8,15 +8,9 @@ import (
 // The sysData type contains all system data. It provides the system-specific underlying implementation. It is guaranteed to have the following by embedding:
 type cSysData struct {
 	ctype			int
-	parentWindow		*sysData
-
-	// for Window
-	closing	chan struct{}
-
-	// for Button
-	clicked	chan struct{}
+	event			chan struct{}
 }
-func (c *cSysData) make(initText string, initWidth int, initHeight int) error {
+func (c *cSysData) make(initText string, initWidth int, initHeight int, window *sysData) error {
 	panic(runtime.GOOS + " sysData does not define make()")
 }
 func (c *cSysData) show() error {