Microsoft Windows tutorial code sets the same variable twice(not my code!).C++

coded in c++, presumably using visual studio.

template <class DERIVED_TYPE> 
class BaseWindow
{
public:
    static LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
    {
        DERIVED_TYPE *pThis = NULL;

        if (uMsg == WM_NCCREATE)
        {
            CREATESTRUCT* pCreate = (CREATESTRUCT*)lParam;
            pThis = (DERIVED_TYPE*)pCreate->lpCreateParams;
            SetWindowLongPtr(hwnd, GWLP_USERDATA, (LONG_PTR)pThis);
            //m_hwnd GETS SET HERE:
            pThis->m_hwnd = hwnd;
        }
        else
        {
            pThis = (DERIVED_TYPE*)GetWindowLongPtr(hwnd, GWLP_USERDATA);
        }
        if (pThis)
        {
            return pThis->HandleMessage(uMsg, wParam, lParam);
        }
        else
        {
            return DefWindowProc(hwnd, uMsg, wParam, lParam);
        }
    }

    BaseWindow() : m_hwnd(NULL) { }

    BOOL Create(
        PCWSTR lpWindowName,
        DWORD dwStyle,
        DWORD dwExStyle = 0,
        int x = CW_USEDEFAULT,
        int y = CW_USEDEFAULT,
        int nWidth = CW_USEDEFAULT,
        int nHeight = CW_USEDEFAULT,
        HWND hWndParent = 0,
        HMENU hMenu = 0
        )
    {
        WNDCLASS wc = {0};

        wc.lpfnWndProc   = DERIVED_TYPE::WindowProc;
        wc.hInstance     = GetModuleHandle(NULL);
        wc.lpszClassName = ClassName();

        RegisterClass(&wc);
        //m_hwnd GETS SET HERE:
        m_hwnd = CreateWindowEx(
            dwExStyle, ClassName(), lpWindowName, dwStyle, x, y,
            nWidth, nHeight, hWndParent, hMenu, GetModuleHandle(NULL), this
            );

        return (m_hwnd ? TRUE : FALSE);
    }

    HWND Window() const { return m_hwnd; }

protected:

    virtual PCWSTR  ClassName() const = 0;
    virtual LRESULT HandleMessage(UINT uMsg, WPARAM wParam, LPARAM lParam) = 0;

    HWND m_hwnd;
};

the variable m_hwnd gets set twice for the same instance(atleast that is how I perceive it):

pThis->m_hwnd = hwnd;

and here:

m_hwnd = CreateWindowEx(
                    dwExStyle, ClassName(), lpWindowName, dwStyle, x, y,
                    nWidth, nHeight, hWndParent, hMenu, GetModuleHandle(NULL), this
                    );

Is there a reason for this? is the m_hwnd actually set only once and i am missing something?

MINIMUM REPRODUCIBLE EXAMPLE:

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
    MainWindow win;

    if (!win.Create(L"Learn to Program Windows", WS_OVERLAPPEDWINDOW))
    {
        return 0;
    }

    ShowWindow(win.Window(), nCmdShow);

    // Run the message loop.

    MSG msg = { };
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

SITE: https://docs.microsoft.com/en-us/windows/win32/learnwin32/managing-application-state-

m_hwnd = CreateWindowEx(
             dwExStyle, ClassName(), lpWindowName, dwStyle, x, y,
             nWidth, nHeight, hWndParent, hMenu, GetModuleHandle(NULL),

 this  /* here you give the instance, Windows will give you this when calling WindowProc */

             );

DERIVED_TYPE *pThis = NULL;

CREATESTRUCT* pCreate = (CREATESTRUCT*)lParam;
pThis = (DERIVED_TYPE*)pCreate->lpCreateParams;