expected<T> make_expected(optional<T> v) { if (v) return make_expected(*v); else make_unexpected(conversion_from_nullopt()); }
expected<void, HRESULT> operator()(HWND hwnd)const{const auto hr = ::DwmEnableBlurBehindWindow(hwnd, &bb);if(SUCCEEDED(hr))return {};return make_unexpected(hr);}