ada binding

ada binding

[Szymon Guz]

Hi,
I've got a very simple question, lets assume that I've got a library 
written in "C++" (e.g. wxWindows) and I want to make an Ada binding. I 
saw that there is a project wxAda, but noone developes that. On the 
wxAda page there is information that between wxWindows and Ada there is 
another layer - it is a C library and I don't understand just one thing: 
how to make an Ada binding for a "C++" class using this C layer ?


regars
Szymon Guz

Re: ada binding

[Maciej Sobczak]

Szymon Guz wrote:

> how to make an Ada binding for a "C++" class using this C layer ?

Basically, if the C++ class is not a template, but just plain "classic" 
OO stuff, then you can write a wrapper around it in C, which will still 
be OO, but without the syntax sugar of real class. Something along this:

// an existing C++ class:
class MyClass
{
public:
     void myFun();
};

// a C wrapper:
extern "C"
void * MyClass_new()
{
     return new MyClass;
}

extern "C"
void MyClass_delete(void *p)
{
     delete static_cast<MyClass*>(p);
}

extern "C"
void MyClass_myFun(void *vp)
{
     MyClass *mcp = static_cast<MyClass*>(vp);
     mcp->myFun();
}

// and so on.

Depending on the level of isolation that you want to achieve and the 
level of type safety that you want to retain, hiding the object behind 
void* might or might not be the best choice, but this is to give you the 
idea. Above, MyClass_new, MyClass_delete and MyClass_myFun are plain C 
functions (you can extract their declarations to separate header file) 
and you can interface them from just about any sensible language in 
existence and from Ada in particular.


-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/

Re: ada binding

[Szymon Guz]

Maciej Sobczak napisał(a):
> Szymon Guz wrote:
> 
>> how to make an Ada binding for a "C++" class using this C layer ?
> 
> Basically, if the C++ class is not a template, but just plain "classic" 
> OO stuff, then you can write a wrapper around it in C, which will still 
> be OO, but without the syntax sugar of real class. Something along this:
> 
> // an existing C++ class:
> class MyClass
> {
> public:
>     void myFun();
> };
> 
> // a C wrapper:
> extern "C"
> void * MyClass_new()
> {
>     return new MyClass;
> }
> 
> extern "C"
> void MyClass_delete(void *p)
> {
>     delete static_cast<MyClass*>(p);
> }
> 
> extern "C"
> void MyClass_myFun(void *vp)
> {
>     MyClass *mcp = static_cast<MyClass*>(vp);
>     mcp->myFun();
> }
> 
> // and so on.
> 
> Depending on the level of isolation that you want to achieve and the 
> level of type safety that you want to retain, hiding the object behind 
> void* might or might not be the best choice, but this is to give you the 
> idea. Above, MyClass_new, MyClass_delete and MyClass_myFun are plain C 
> functions (you can extract their declarations to separate header file) 
> and you can interface them from just about any sensible language in 
> existence and from Ada in particular.
> 
> 

OK, but what about using the class fields :

class MyClass
{
public:
   int X;
   int *p_X;
}

and what about inheriting this from the class in Ada, is it possible ?

regards
Szymon Guz

Re: ada binding

[Georg Bauhaus]

On Thu, 2006-02-09 at 16:56 +0100, Szymon Guz wrote:


> 
> OK, but what about using the class fields :
> 
> class MyClass
> {
> public:
>    int X;
>    int *p_X;
> }
> 
> and what about inheriting this from the class in Ada, is it possible ?
> 

This tends to be compiler specific AFAICT.
At least Aonix and AdaCore explain what you can do
to make a C++ OO type available to an Ada program.

If you have some "generalized" OO architecture
like with CORBA or .NET or Mono, binding to an OO module
should be easier.

-- Georg 

Re: ada binding

[Martin Krischik]

Szymon Guz wrote:

> Maciej Sobczak napisa?(a):
>> Szymon Guz wrote:
>> 
>>> how to make an Ada binding for a "C++" class using this C layer ?
>> 
>> Basically, if the C++ class is not a template, but just plain "classic"
>> OO stuff, then you can write a wrapper around it in C, which will still
>> be OO, but without the syntax sugar of real class. Something along this:
>> 
>> // an existing C++ class:
>> class MyClass
>> {
>> public:
>>     void myFun();
>> };
>> 
>> // a C wrapper:
>> extern "C"
>> void * MyClass_new()
>> {
>>     return new MyClass;
>> }
>> 
>> extern "C"
>> void MyClass_delete(void *p)
>> {
>>     delete static_cast<MyClass*>(p);
>> }
>> 
>> extern "C"
>> void MyClass_myFun(void *vp)
>> {
>>     MyClass *mcp = static_cast<MyClass*>(vp);
>>     mcp->myFun();
>> }
>> 
>> // and so on.
>> 
>> Depending on the level of isolation that you want to achieve and the
>> level of type safety that you want to retain, hiding the object behind
>> void* might or might not be the best choice, but this is to give you the
>> idea. Above, MyClass_new, MyClass_delete and MyClass_myFun are plain C
>> functions (you can extract their declarations to separate header file)
>> and you can interface them from just about any sensible language in
>> existence and from Ada in particular.
>> 
>> 
> 
> OK, but what about using the class fields :
> 
> class MyClass
> {
> public:
>    int X;
>    int *p_X;
> }
> 
> and what about inheriting this from the class in Ada, is it possible ?

If you are planning to inheriting  then you need to directly bind to the C++
class. Only one compiler offers that (GNAT). Start reading here:

http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gnat_rm/Pragma-CPP_005fClass.html

Martin
-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com

Re: ada binding

[Szymon Guz]

Martin Krischik napisał(a):
> Szymon Guz wrote:
> 
>> Maciej Sobczak napisa?(a):
>>> Szymon Guz wrote:
>>>
>>>> how to make an Ada binding for a "C++" class using this C layer ?
>>> Basically, if the C++ class is not a template, but just plain "classic"
>>> OO stuff, then you can write a wrapper around it in C, which will still
>>> be OO, but without the syntax sugar of real class. Something along this:
>>>
>>> // an existing C++ class:
>>> class MyClass
>>> {
>>> public:
>>>     void myFun();
>>> };
>>>
>>> // a C wrapper:
>>> extern "C"
>>> void * MyClass_new()
>>> {
>>>     return new MyClass;
>>> }
>>>
>>> extern "C"
>>> void MyClass_delete(void *p)
>>> {
>>>     delete static_cast<MyClass*>(p);
>>> }
>>>
>>> extern "C"
>>> void MyClass_myFun(void *vp)
>>> {
>>>     MyClass *mcp = static_cast<MyClass*>(vp);
>>>     mcp->myFun();
>>> }
>>>
>>> // and so on.
>>>
>>> Depending on the level of isolation that you want to achieve and the
>>> level of type safety that you want to retain, hiding the object behind
>>> void* might or might not be the best choice, but this is to give you the
>>> idea. Above, MyClass_new, MyClass_delete and MyClass_myFun are plain C
>>> functions (you can extract their declarations to separate header file)
>>> and you can interface them from just about any sensible language in
>>> existence and from Ada in particular.
>>>
>>>
>> OK, but what about using the class fields :
>>
>> class MyClass
>> {
>> public:
>>    int X;
>>    int *p_X;
>> }
>>
>> and what about inheriting this from the class in Ada, is it possible ?
> 
> If you are planning to inheriting  then you need to directly bind to the C++
> class. Only one compiler offers that (GNAT). Start reading here:
> 
> http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gnat_rm/Pragma-CPP_005fClass.html
> 
> Martin

I know but I wander if I can do that using other compilers and with the 
middle layer written in C.

regards
Szymon Guz

Re: ada binding

[Martin Krischik]

Szymon Guz wrote:

> Martin Krischik napisa?(a):
>> Szymon Guz wrote:
>> 
>>> Maciej Sobczak napisa?(a):
>>>> Szymon Guz wrote:
>>>>
>>>>> how to make an Ada binding for a "C++" class using this C layer ?
>>>> Basically, if the C++ class is not a template, but just plain "classic"
>>>> OO stuff, then you can write a wrapper around it in C, which will still
>>>> be OO, but without the syntax sugar of real class. Something along
>>>> this:
>>>>
>>>> // an existing C++ class:
>>>> class MyClass
>>>> {
>>>> public:
>>>>     void myFun();
>>>> };
>>>>
>>>> // a C wrapper:
>>>> extern "C"
>>>> void * MyClass_new()
>>>> {
>>>>     return new MyClass;
>>>> }
>>>>
>>>> extern "C"
>>>> void MyClass_delete(void *p)
>>>> {
>>>>     delete static_cast<MyClass*>(p);
>>>> }
>>>>
>>>> extern "C"
>>>> void MyClass_myFun(void *vp)
>>>> {
>>>>     MyClass *mcp = static_cast<MyClass*>(vp);
>>>>     mcp->myFun();
>>>> }
>>>>
>>>> // and so on.
>>>>
>>>> Depending on the level of isolation that you want to achieve and the
>>>> level of type safety that you want to retain, hiding the object behind
>>>> void* might or might not be the best choice, but this is to give you
>>>> the idea. Above, MyClass_new, MyClass_delete and MyClass_myFun are
>>>> plain C functions (you can extract their declarations to separate
>>>> header file) and you can interface them from just about any sensible
>>>> language in existence and from Ada in particular.
>>>>
>>>>
>>> OK, but what about using the class fields :
>>>
>>> class MyClass
>>> {
>>> public:
>>>    int X;
>>>    int *p_X;
>>> }
>>>
>>> and what about inheriting this from the class in Ada, is it possible ?
>> 
>> If you are planning to inheriting  then you need to directly bind to the
>> C++ class. Only one compiler offers that (GNAT). Start reading here:
>> 
>> http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gnat_rm/Pragma-CPP_005fClass.html
>> 
>> Martin
> 
> I know but I wander if I can do that using other compilers and with the
> middle layer written in C.

You would need to use proxy classes then. Just as much work :-(

Martin

-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com

Re: ada binding

[sg]

Martin Krischik napisał(a):
> Szymon Guz wrote:
> 
>> Martin Krischik napisa?(a):
>>> Szymon Guz wrote:
>>>
>>>> Maciej Sobczak napisa?(a):
>>>>> Szymon Guz wrote:
>>>>>
>>>>>> how to make an Ada binding for a "C++" class using this C layer ?
>>>>> Basically, if the C++ class is not a template, but just plain "classic"
>>>>> OO stuff, then you can write a wrapper around it in C, which will still
>>>>> be OO, but without the syntax sugar of real class. Something along
>>>>> this:
>>>>>
>>>>> // an existing C++ class:
>>>>> class MyClass
>>>>> {
>>>>> public:
>>>>>     void myFun();
>>>>> };
>>>>>
>>>>> // a C wrapper:
>>>>> extern "C"
>>>>> void * MyClass_new()
>>>>> {
>>>>>     return new MyClass;
>>>>> }
>>>>>
>>>>> extern "C"
>>>>> void MyClass_delete(void *p)
>>>>> {
>>>>>     delete static_cast<MyClass*>(p);
>>>>> }
>>>>>
>>>>> extern "C"
>>>>> void MyClass_myFun(void *vp)
>>>>> {
>>>>>     MyClass *mcp = static_cast<MyClass*>(vp);
>>>>>     mcp->myFun();
>>>>> }
>>>>>
>>>>> // and so on.
>>>>>
>>>>> Depending on the level of isolation that you want to achieve and the
>>>>> level of type safety that you want to retain, hiding the object behind
>>>>> void* might or might not be the best choice, but this is to give you
>>>>> the idea. Above, MyClass_new, MyClass_delete and MyClass_myFun are
>>>>> plain C functions (you can extract their declarations to separate
>>>>> header file) and you can interface them from just about any sensible
>>>>> language in existence and from Ada in particular.
>>>>>
>>>>>
>>>> OK, but what about using the class fields :
>>>>
>>>> class MyClass
>>>> {
>>>> public:
>>>>    int X;
>>>>    int *p_X;
>>>> }
>>>>
>>>> and what about inheriting this from the class in Ada, is it possible ?
>>> If you are planning to inheriting  then you need to directly bind to the
>>> C++ class. Only one compiler offers that (GNAT). Start reading here:
>>>
>>> http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gnat_rm/Pragma-CPP_005fClass.html
>>>
>>> Martin
>> I know but I wander if I can do that using other compilers and with the
>> middle layer written in C.
> 
> You would need to use proxy classes then. Just as much work :-(
> 
> Martin
> 

Well... if this is the only way, so I think that there a very little 
chance for having the wxWindows Ada binding

Szymon Guz

Re: ada binding

[Martin Krischik]

sg wrote:

> Well... if this is the only way, so I think that there a very little
> chance for having the wxWindows Ada binding

Or any other binding. I don't think an Ada binding to wxWindows  is more
work then a Fortran 2003 binding would be (once Fortan 2003 becomes
available).

And it's the same for any large C++ library. There are several large
projects for KDE which want to make KDE available to other languages. Most
of those use then C/Proxy class approach as well.

The problem is that the C++ compilation model does not lend itself to
automated generation of binding files. All the #if, #defined and #include
are in the way. At least the usual implementation of #include - the ISO
standard  allows implementations not using a plain text file.

Martin
-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com

Re: ada binding

[Lucretia]

Martin Krischik wrote:
> sg wrote:
>
> > Well... if this is the only way, so I think that there a very little
> > chance for having the wxWindows Ada binding
>
> Or any other binding. I don't think an Ada binding to wxWindows  is more
> work then a Fortran 2003 binding would be (once Fortan 2003 becomes
> available).

Have no clue about this ;-D

> And it's the same for any large C++ library. There are several large
> projects for KDE which want to make KDE available to other languages. Most
> of those use then C/Proxy class approach as well.

It's the easiest, most portable method.

> The problem is that the C++ compilation model does not lend itself to
> automated generation of binding files. All the #if, #defined and #include
> are in the way. At least the usual implementation of #include - the ISO
> standard  allows implementations not using a plain text file.

Yup, in wxAda, I've decided to add dummy primitives where functions
differ for different platforms. For example, there is a function in
wxFrame (can't remember which one off the top of my head) which is only
available under Win32, so in wxAda I just have a null sub program for
other platforms, calling it isn't really going to matter and will only
effect Win32.

Luke.

Re: ada binding

[Martin Dowie]

Martin Krischik wrote:
> If you are planning to inheriting  then you need to directly bind to the C++
> class. Only one compiler offers that (GNAT). Start reading here:
> 
> http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gnat_rm/Pragma-CPP_005fClass.html

Don't think this is true...

ObjectAda 8.2 comes with a manual "Ada Binding Technology C++ Mapping 
Guide  Version 3.1"

I suspect that pretty much every Ada compiler comes with some mechanism 
to do this - shame it isn't standardized.

Cheers

-- Martin

Re: ada binding

[Lucretia]

Szymon Guz wrote:
> Hi,
> I've got a very simple question, lets assume that I've got a library
> written in "C++" (e.g. wxWindows) and I want to make an Ada binding. I
> saw that there is a project wxAda, but noone developes that. On the

Actually, I do. It's not got very far yet, as it's extremely confusing
and time consuming and I just haven't had the time to do it.

> wxAda page there is information that between wxWindows and Ada there is
> another layer - it is a C library and I don't understand just one thing:
> how to make an Ada binding for a "C++" class using this C layer ?

As the other poster has pointed out, the C layer is what the Ada code
interfaces with. Inside the Ada layer it is then possible to inherit
from the C++ classes.

The idea of wxAda is provide wxWidgets for any Ada compiler, not just
those that *can* import C++ libraries - but saying that, when you
interface with C++ libraries you end up with a C++ like library in Ada
- not very Ada like.

Luke.

P.S: the source isn't anywhere near ready yet.