"operator" overloading?

[Dmitry Olshansky]

On 23.02.2011 21:48, Simon wrote:
> On 23/02/2011 18:42, Simon wrote:
>> On 23/02/2011 14:37, Dmitry Olshansky wrote:
>>> On 23.02.2011 17:08, %u wrote:
>>>> Hi everyone,
>>>>
>>>> Was hoping someone could help me make sense of this bit of C++ code:
>>>>
>>>> class canvas
>>>> {
>>>> operator HDC() { return _hdc; }
>>>> protected:
>>>> canvas(HDC hdc): _hdc(hdc) {}
>>>> HDC _hdc;
>>>> }
>>>>
>>>> From what I understand, HDC is an alias for HANDLE in Windows. So
>>>> they are overloading canvas such that when assigned to handle
>>>> instance it returns _hdc? How is this done in D?
>>>>
>>>> Thanks
>>>
>>> Something like this, and i shouldn't be a class in D (it's a proxy sort
>>> of, right? ) :
>>>
>>> struct canvas{
>>> alias getHandle this;
>>> this(HDC hdc){
>>> _hdc = hdc;
>>> }
>>> @property HDC getHandle(){ return _hdc; }
>>> private:
>>> HDC _hdc;
>>> }
>>>
>>> uinttest{
>>> HDC h = cast(HDC)1;
>>> canvas c = h;//intitalize
>>> h = c;
>>> assert(h == c);
>>> }
>>>
>>
>> That's the wrong way round.
>
> Nuts never mind. I'm talking out my ass.
> Though how do you do it using the cast operator?
> That would be closer to the c++ implementation.
>
There is no much point in getting closer to the source I think.
Well, there sort of was opImplicitCast, but it's functionality is 
superseded by alias this.
When multiple alias this are implemented and some bugs fixed we are sure 
to witness it's full power.

Meanwhile you could just as well make this proxy a template struct:
struct proxy(T){
    alias getHandle this;
    this(T handle){
      _h = handle;
    }
    @property  T getHandle(){ return _h; }
private:
     T _h;
}
alias proxy!(HDC) canvas;
//and so on and so forth

But this sort of thin wrappers are of no good if they do not provide
you some benefits like automatic resource management and such.

-- 
Dmitry Olshansky