Hi,
I have a small problem in translating C++ operator overloading to D

// Allready translated C++ stuff
class CFont
{
public:
  HFONT m_hFont;

  this(HFONT hFont = NULL)
  {
    m_hFont = hFont;
  }
  ~this()
  {
    if(m_hFont !is NULL && !DeleteObject(m_hFont))
    m_hFont = NULL;
  }

// TODO How to translate this C++ construct  into D

    operator HFONT() {return m_hFont;}

// That's the problem.

Sorry have  not found anything related in the docs.
Some ideas;;; Many thanks in advance.
Bjoern

BLS wrote:
> Hi,
> I have a small problem in translating C++ operator overloading to D
> 
> // Allready translated C++ stuff
> class CFont
> {
> public:
>   HFONT m_hFont;
> 
>   this(HFONT hFont = NULL)
>   {
>     m_hFont = hFont;
>   }
>   ~this()
>   {
>     if(m_hFont !is NULL && !DeleteObject(m_hFont))
>     m_hFont = NULL;
>   }
> 
> // TODO How to translate this C++ construct  into D
> 
>     operator HFONT() {return m_hFont;}
> 
> // That's the problem.
> 
> Sorry have  not found anything related in the docs.
> Some ideas;;; Many thanks in advance.
> Bjoern

Basically you can't until D gets something like opImplicitCast.

What that does is allow the CFont class to be used in contexts where an HFONT is expected.

so you need to make it into a function that explicity does the cast. Such as:

     HFONT hfont() {return m_hFont;}

or name it to_HFONT() or as_hfont() or whatever tickles your fancy.

This is one of the bigger pains of translating C++ code to D -- the repercussions of not having something like opImplicitCast.  Chances are the original code will be passing CFonts around as HFONTS willy-nilly. So you're going to have to add a lot of ".hfont"s  here and there to make the translated code compile.


--bb

Bill Baxter schrieb:
> BLS wrote:
>> Hi,
>> I have a small problem in translating C++ operator overloading to D
>>
>> // Allready translated C++ stuff
>> class CFont
>> {
>> public:
>>   HFONT m_hFont;
>>
>>   this(HFONT hFont = NULL)
>>   {
>>     m_hFont = hFont;
>>   }
>>   ~this()
>>   {
>>     if(m_hFont !is NULL && !DeleteObject(m_hFont))
>>     m_hFont = NULL;
>>   }
>>
>> // TODO How to translate this C++ construct  into D
>>
>>     operator HFONT() {return m_hFont;}
>>
>> // That's the problem.
>>
>> Sorry have  not found anything related in the docs.
>> Some ideas;;; Many thanks in advance.
>> Bjoern
> 
> Basically you can't until D gets something like opImplicitCast.
> 
> What that does is allow the CFont class to be used in contexts where an HFONT is expected.
> 
> so you need to make it into a function that explicity does the cast. Such as:
> 
>      HFONT hfont() {return m_hFont;}
> 
> or name it to_HFONT() or as_hfont() or whatever tickles your fancy.

Sorry, I don't understand. But before I ask for more information, I'll study the C++ code again.
> 
> This is one of the bigger pains of translating C++ code to D -- the repercussions of not having something like opImplicitCast.  Chances are the original code will be passing CFonts around as HFONTS willy-nilly. So you're going to have to add a lot of ".hfont"s  here and there to make the translated code compile.
> 
> 
> --bb
Ouch!
Any plans for opImplicitCast in D 2 ?

A bit off topic
Bill, you have just translated a huge C++ project. Can you tell us a bit  about your experience, problems, tricks ...probabely on D WIKI.

I am going to translate about 15000 LOC (99 percent template free, thanks man) and I know about at least 2 guys working on bigger C++ to D projects. I have allready suggested to open a new forum "porting C++" but the feedback was not really enthusiastic, to say the least.
However, I am pretty sure that information regarding porting C++ to D is a matter of interest.
Bjoern

BLS wrote:
> Bill Baxter schrieb:
>> BLS wrote:
>>> Hi,
>>> I have a small problem in translating C++ operator overloading to D
>>>
>>> // Allready translated C++ stuff
>>> class CFont
>>> {
>>> public:
>>>   HFONT m_hFont;
>>>
>>>   this(HFONT hFont = NULL)
>>>   {
>>>     m_hFont = hFont;
>>>   }
>>>   ~this()
>>>   {
>>>     if(m_hFont !is NULL && !DeleteObject(m_hFont))
>>>     m_hFont = NULL;
>>>   }
>>>
>>> // TODO How to translate this C++ construct  into D
>>>
>>>     operator HFONT() {return m_hFont;}
>>>
>>> // That's the problem.
>>>
>>> Sorry have  not found anything related in the docs.
>>> Some ideas;;; Many thanks in advance.
>>> Bjoern
>>
>> Basically you can't until D gets something like opImplicitCast.
>>
>> What that does is allow the CFont class to be used in contexts where an HFONT is expected.
>>
>> so you need to make it into a function that explicity does the cast. Such as:
>>
>>      HFONT hfont() {return m_hFont;}
>>
>> or name it to_HFONT() or as_hfont() or whatever tickles your fancy.
> 
> Sorry, I don't understand. But before I ask for more information, I'll study the C++ code again.

operator SOMETYPE() in C++ is a casting/conversion operator.
http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=24&rl=1

So with your example, given some API like
  SetFont(HFONT font);

That operator HFONT makes it so you can pass a CFont to that function as if it were an HFONT.

   CFont mycfont;
   ...
   SetFont(mycfont);
     // first calls operator HFONT() and passes result to SetFont

>> This is one of the bigger pains of translating C++ code to D -- the repercussions of not having something like opImplicitCast.  Chances are the original code will be passing CFonts around as HFONTS willy-nilly. So you're going to have to add a lot of ".hfont"s  here and there to make the translated code compile.
>>
>>
>> --bb
> Ouch!
> Any plans for opImplicitCast in D 2 ?

Apparently so according to WalterAndrei.pdf.

> A bit off topic
> Bill, you have just translated a huge C++ project. Can you tell us a bit  about your experience, problems, tricks ...probabely on D WIKI.

I was thinking about it, but I wasn't sure if anyone would be interested.

> I am going to translate about 15000 LOC (99 percent template free, thanks man) and I know about at least 2 guys working on bigger C++ to D projects. I have allready suggested to open a new forum "porting C++" but the feedback was not really enthusiastic, to say the least.

To me the D newsgroup is a fine place to discuss porting issues.  And a wiki with advice would be nice -- especially for people who want to port something but don't really know C++ that well to begin with.

> However, I am pretty sure that information regarding porting C++ to D is a matter of interest.

Well, if you think so I can jot down some of my observations about porting from C++ to D on wiki4d.

--bb