On Tuesday, 26 May 2020 at 12:08:29 UTC, Johannes Loher wrote:
> [...]

Small correction: I said that this is an lvalue and that you cannot take the address of lvalues. Of course that is incorrect, I meant to say that rvalues (this is an rvalue and you cannot take the address of rvalues).

On Monday, 25 May 2020 at 16:26:31 UTC, Vinod K Chandran wrote:
> Here is my full code. Please take a look.
> https://pastebin.com/av3nrvtT

Change line 124 to:

SetWindowSubclass(this.mHandle, SUBCLASSPROC(&btnWndProc), UINT_PTR(subClsID), cast(DWORD_PTR)cast(void*)this);

That is, change `&this` to `cast(void*)this`.

On Tuesday, 26 May 2020 at 12:41:20 UTC, John Chapman wrote:
> On Monday, 25 May 2020 at 16:26:31 UTC, Vinod K Chandran wrote:
>> Here is my full code. Please take a look.
>> https://pastebin.com/av3nrvtT
>
> Change line 124 to:
>
> SetWindowSubclass(this.mHandle, SUBCLASSPROC(&btnWndProc), UINT_PTR(subClsID), cast(DWORD_PTR)cast(void*)this);
>
> That is, change `&this` to `cast(void*)this`.

Hi,
Thanks for the reply. That will work like charm but we need to change the code in subclassed button's WndProc  like this--
extern(Windows)
private LRESULT btnWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam, UINT_PTR scID, DWORD_PTR refData) {
    try  {

        Button thisBtn = cast(Button)cast(void*)refData;
     {
    catch (Exception e) {}
    ....

On Tuesday, 26 May 2020 at 12:08:29 UTC, Johannes Loher wrote:
> On Tuesday, 26 May 2020 at 11:44:58 UTC, Vinod K Chandran wrote:
>> [...]
>
>> [...]
> It doesn't compile, the line
>
> string mt
>
> [...]

Hi,
Sorry for the typos in my code.

On Tuesday, 26 May 2020 at 13:37:22 UTC, Vinod K Chandran wrote:
> On Tuesday, 26 May 2020 at 12:41:20 UTC, John Chapman wrote:
>> On Monday, 25 May 2020 at 16:26:31 UTC, Vinod K Chandran wrote:
>>> Here is my full code. Please take a look.
>>> https://pastebin.com/av3nrvtT
>>
>> Change line 124 to:
>>
>> SetWindowSubclass(this.mHandle, SUBCLASSPROC(&btnWndProc), UINT_PTR(subClsID), cast(DWORD_PTR)cast(void*)this);
>>
>> That is, change `&this` to `cast(void*)this`.
>
> Hi,
> Thanks for the reply. That will work like charm but we need to change the code in subclassed button's WndProc  like this--
> extern(Windows)
> private LRESULT btnWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam, UINT_PTR scID, DWORD_PTR refData) {
>     try  {
>
>         Button thisBtn = cast(Button)cast(void*)refData;
>      {
>     catch (Exception e) {}
>     ....

So far now, two solutions are very clear for this problem.
1. As per John Chapman's suggestion - use cast(DWORD_PTR)cast(void*)this).
2. Use another varibale to use as an lvalue. -
     Button dummyBtn = this;
     cast(DWORD_PTR)&dummyBtn;
Among these two, i think 2nd option is good. Am i right ?

On Tuesday, 26 May 2020 at 11:35:23 UTC, Vinod K Chandran wrote:
> Okay, but uint is working perfectly.

It won't if you use -m64.

On 26.05.20 15:43, Vinod K Chandran wrote:
> So far now, two solutions are very clear for this problem.
> 1. As per John Chapman's suggestion - use cast(DWORD_PTR)cast(void*)this).
> 2. Use another varibale to use as an lvalue. -
>       Button dummyBtn = this;
>       cast(DWORD_PTR)&dummyBtn;
> Among these two, i think 2nd option is good. Am i right ?

No. Use option 1.

On Tuesday, 26 May 2020 at 13:48:52 UTC, ag0aep6g wrote:
> On 26.05.20 15:43, Vinod K Chandran wrote:
>> So far now, two solutions are very clear for this problem.
>> 1. As per John Chapman's suggestion - use cast(DWORD_PTR)cast(void*)this).
>> 2. Use another varibale to use as an lvalue. -
>>       Button dummyBtn = this;
>>       cast(DWORD_PTR)&dummyBtn;
>> Among these two, i think 2nd option is good. Am i right ?
>
> No. Use option 1.

Could you please tell me why ?

On Tuesday, 26 May 2020 at 13:44:24 UTC, Adam D. Ruppe wrote:
> On Tuesday, 26 May 2020 at 11:35:23 UTC, Vinod K Chandran wrote:
>> Okay, but uint is working perfectly.
>
> It won't if you use -m64.

Okay. I got it.

Am 26.05.20 um 16:17 schrieb Vinod K Chandran:
> On Tuesday, 26 May 2020 at 13:48:52 UTC, ag0aep6g wrote:
>> On 26.05.20 15:43, Vinod K Chandran wrote:
>>> So far now, two solutions are very clear for this problem.
>>> 1. As per John Chapman's suggestion - use
>>> cast(DWORD_PTR)cast(void*)this).
>>> 2. Use another varibale to use as an lvalue. -
>>>       Button dummyBtn = this;
>>>       cast(DWORD_PTR)&dummyBtn;
>>> Among these two, i think 2nd option is good. Am i right ?
>>
>> No. Use option 1.
> 
> Could you please tell me why ?
With option 2, you will not actually get a pointer to the object but a pointer to the local variable which is a reference to the object. `this` and the local variable both are references to the object, so internally they already are pointers. Their usage is just restricted in regular D code. This is also why simply casting it to a pointer works. You need to cast to void* in between because that's just the way to tell the compiler to ignore the restrictions you usually have for references.