Is there a way to create an elegant class-member window-function?

[Andrej Mitrovic]

I don't know of any /elegant/ way of doing it, but a hash mapping
HWND's to Objects is usually how it's done. This is how DFL, DGUI, and
Harmonia work.

You can check out the function "winDispatch" in my sample
win32_window_framework here:
https://github.com/AndrejMitrovic/cairoDSamples

Alternatively see those GUI libs to see how it's done.