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digitalmars.D.learn - C++ operator overloading to D

reply BLS <nanali nospam-wanadoo.fr> writes:
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
Sep 22 2007
parent reply Bill Baxter <dnewsgroup billbaxter.com> writes:
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
Sep 22 2007
parent reply BLS <nanali nospam-wanadoo.fr> writes:
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
Sep 22 2007
parent Bill Baxter <dnewsgroup billbaxter.com> writes:
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
Sep 22 2007