Member modified by method reverts after it exits - oop

Question

I have a window (Windows), and my wndProc is basically the same as the one on the windows guides. However, even though WM_CLOSE gets passed (and I can use if(msg == WM_CLOSE)), I can't seem to set my shouldClose flag. I've confirmed that I still get the event within my processMessage method. So my question is this: what is going on, and how can I make it work?
Edit: I tried storing the window data as a struct instead of a class, and everything works just fine. Ie. All I changed was the type of the class, and a few errors.
class Win32Window {
this(wstring title, int width, int height) {
immutable wstring className = "glass_def_class_name\0";
auto hInstance = GetModuleHandle(null);
WNDCLASSW wc;
wc.lpfnWndProc = &windowProc;
wc.hInstance = hInstance;
wc.lpszClassName = &className[0];
RegisterClassW(&wc);
handle = CreateWindowExW(
0,
&className[0],
&title[0],
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT,
width, height,
null, null,
hInstance,
cast(void*) this);
ShowWindow(handle, SW_NORMAL);
}
~this() {
DestroyWindow(handle);
}
void processEvents() {
MSG msg;
while (PeekMessage(&msg, handle, 0, 0, PM_REMOVE)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
bool shouldClose;
HWND handle;
private:
LRESULT processMessage(UINT msg, WPARAM wp, LPARAM lp) nothrow {
switch (msg) {
case WM_CLOSE:
shouldClose = true;
return 0;
default:
return DefWindowProc(handle, msg, wp, lp);
}
}
}
private extern (Windows) LRESULT windowProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) nothrow {
Win32Window window;
if (msg == WM_CREATE) {
CREATESTRUCT* create = cast(CREATESTRUCT*) lp;
window = cast(Win32Window*) create.lpCreateParams;
SetWindowLongPtr(hwnd, GWLP_USERDATA, cast(LONG_PTR) create.lpCreateParams);
window.handle = hwnd;
}
else {
LONG_PTR ptr = GetWindowLongPtr(hwnd, GWLP_USERDATA);
window = cast(Win32Window* ptr);
}
if (window)
return window.processMessage(msg, wp, lp);
else
return DefWindowProc(hwnd, msg, wp, lp);
}
void main()
{
auto window = new Win32Window("test", 1280, 720);
while(window.shouldClose == false) {
window.processEvents();
}
window.destroy();
}

Answer 1

Member modified by method reverts after it exits
this was when you worked with local copy of object, and make modification to this local copy, but not really to object. I not view another explanations
inside windowProc you do next Win32Window window = *(cast(Win32Window*) ptr); - so you make local copy of your initial object state in windowProc and then do all modification to this local copy - of course all it lost when you exit from windowProc correct code must be next:
private LRESULT windowProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) nothrow {
Win32Window* window;
if (msg == WM_NCCREATE) {
CREATESTRUCT* create = (CREATESTRUCT*) lp;
window = (Win32Window*) create.lpCreateParams;
SetWindowLongPtr(hwnd, GWLP_USERDATA, (LONG_PTR) create.lpCreateParams);
window.handle = hwnd;
}
else {
window = (Win32Window*)GetWindowLongPtr(hwnd, GWLP_USERDATA);
}
return window ? window->processMessage(msg, wp, lp) : DefWindowProc(hwnd, msg, wp, lp);
}

Answer 2

It turns out that you can't actually cast a pointer directly to a reference. An intermediary is necessary (or something to that effect). Thus, the winProc should look something like this:
private extern (Windows) LRESULT windowProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) nothrow {
Win32Window window;
if (msg == WM_NCCREATE) {
auto create = cast(CREATESTRUCT*) lp;
window = cast(Win32Window) (cast(void*) create.lpCreateParams);
window.handle = hwnd;
SetWindowLongPtr(hwnd, GWLP_USERDATA, cast(LONG_PTR) create.lpCreateParams);
}
else {
window = cast(Win32Window) (cast(void*) GetWindowLongPtr(hwnd, GWLP_USERDATA));
}
return window ? window.processMessage(msg, wp, lp) : DefWindowProc(hwnd, msg, wp, lp);
}
Note the extra cast(void*) before create.lpCreateParams and GetWindowLongPtr(hwnd, GWLP_USERDATA). I'm not entirely sure why this works as opposed to my original code, but it seems to work, and I'll do some more investigating when I have the time.