C++ cast to D cast again :)

[BLS]

div0 schrieb:
> BLS wrote:
>> Hi and sorry about picking on your nerves again  :(
>> // C++
>> class CWin
>> {
>> //
>> static LRESULT CALLBACK WndProc(HWND hWnd, UINT uID, WPARAM wParam, 
>> LPARAM lParam)
>> {
>>   CWin* pWnd=NULL;  // init pWnd
>> }
>>
>> // later ...
>> CWin* pChild=reinterpret_cast<CWin*>((HWND)
>> ::GetWindowLong(pWnd->GetDlgItem( ((( LPDRAWITEMSTRUCT 
>> )lParam)->CtlID) ),GWL_USERDATA) );
>>
>>
>> }
>>
>> //our D class
>> class CWin
>> {
>> static LRESULT WndProc(HWND hWnd, UINT uID, WPARAM wParam, LPARAM lParam)
>> {
>>   CWin pWnd=null;  // init pWnd as    ---reference !
>> }
>> /* instead of :
>> CWin* pChild=reinterpret_cast<CWin*>
>> we use
>> CWin pChild = cast(CWin) cast(void*)
>>
>> But I am not sure how to translate :
>> ((HWND)
>> ::GetWindowLong(pWnd->GetDlgItem( ((( LPDRAWITEMSTRUCT 
>> )lParam)->CtlID) ),GWL_USERDATA) );
>> */
>>
>> // Later we have
>> if (HIWORD(pWnd))
>>
>> /*Since we are working with a ref. instead of a pointer this will not 
>> work.
>> I guess I can use :
>> */
>>
>> if (HIWORD(cast(void*)pWnd))
>> // can you confirm
>> }
>>
>> GetWindowLong() is a Windows Api func., sure you know it.
>> So what the correct translation ?
>> Bjoern
>> Beside, I still wonder : Having a class A, Is A* pA a legal construct 
>> in D.
>> What is pA from a technical view; a pointer to a reference ?
> 
> Even if you get this to compile it won't work.
> (well it will till one day until it just crashes mysteriously)
> 
> At some point the garbage collector might decide move your Cwin object, 
> invalidating the pointer you are trying to store with 
> SetWindowLong/GetWindowLong.
> 

Thanks div0,
I am allready afraid that this is the case...

> You'll have to either allocation your cwin objects outside the garbage 
> collectors control or pin the objects. (Don't know how you do this, 
> depends on whether you are using phobos or tango)
> 

Tango.

What means "pin the object", please explain.
Bjoern


> You should probably look at how dfl interfaces with the Win32 API, 
> http://www.dprogramming.com/dfl.ph as that library has solved these 
> issues and you should be able to work out how it's doing all the 
> necessary casting/pinning.