window_class::Register

Continuing the look at window_class. here are the Register methods. Each one will initialize defaults for WNDCLASSEX then allow the window implementation to override the defaults by calling window_class_register via ADL. Then it will force the WNDPROC to WindowCallback and call Register.

template<typename WindowClassTag>
//static
ATOM window_class<WindowClassTag>::Register()
{
  WNDCLASSEX wcex = {};
  wcex.cbSize = sizeof(WNDCLASSEX);

  // defaults that can be overriden
  wcex.style = CS_HREDRAW | CS_VREDRAW;
  wcex.hInstance = GetCurrentInstance();
  wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);

  window_class_register(&wcex, tag());

  // not overridable
  wcex.lpfnWndProc = WindowCallback<WindowClassTag>;

  return RegisterClassEx(&wcex);
}

The default overload does the bare minimum

template<typename WindowClassTag>
template<typename T>
//static
ATOM window_class<WindowClassTag>::Register(T && t)
{
  WNDCLASSEX wcex = {};
  wcex.cbSize = sizeof(WNDCLASSEX);

  // defaults that can be overriden
  wcex.style = CS_HREDRAW | CS_VREDRAW;
  wcex.hInstance = GetCurrentInstance();
  wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);

  window_class_register(std::forward<T>(t), &wcex, tag());

  // not overridable
  wcex.lpfnWndProc = WindowCallback<WindowClassTag>;

  return RegisterClassEx(&wcex);
}

This overload will accept a parameter, any parameter that the implementation desires to require, it could even be a fully filled out WNDCLASSEX that is just copied over the defaults.