// error handling could be improved too
 
template <typename T>
using ToPointer = typename std::add_pointer<typename std::remove_reference<Fun>::type>::type;
 
template <typename Fun>
BOOL CALLBACK AdaptEnumWindowsProc(HWND hwnd, LPARAM lParam) {
    Fun& fun = *reinterpret_cast<ToPointer<Fun>>(lparam); // what's the correct cast?
    return fun(hwnd);
}
 
template <typename Fun>
BOOL BetterEnumWindows(Fun&& fun) {
    return ::EnumWindows(&AdaptEnumWindowsProc<Fun>, reinterpret_cast<LPARAM>(&fun));
}
 
 

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