Re: [Texmacs-dev] Re: Compiling TexMacs on OSX

[Henri Lesourd]

Josef Weidendorfer wrote:

> Hi,
>
> from an outside view, I find this discussion quite interesting...
> But IMHO the arguments about the need for C wrappers for plugins
> is wrong.
>
> [...]
>  
>
> When both a Texmacs binary and an independently compiled
> plugin want to use a given class, it should be enough to
> pass pointers between.
Not if you want to directly call the methods from
inside the surrounding code (i.e., the one which
loads the DLL).


> For this, you use factory methods
> in the plugin, and the created objects can be used in the
> texmacs binary without any need for recompilation.
>
>  
It seems to amount to the fact that any direct
method call should happen inside the plugin code,
thus it amounts to the need of exporting the C++
methods thru a C API (i.e.: wrapping each one of
the methods behind an exported C function).


> E.g. when texmacs defines a C++ class Button, the plugin is
> free to derive from this class and define a MySuperButton,
> and can pass such objects to the texmacs binary via a factory
> method. As long as texmacs is only storing the object pointer
> or calling methods from the base class Button, all goes well.
>
>  
It seems to me that this technique would only work
if you use the same compiler for compiling TeXmacs
and the DLL.

Or am I wrong here ? How can you have a method call
using the dispatch of the compiler A, while having
the vtables and the body of the method using the
dispatch technique of the compiler B ?


> > Excuse me, but when I look at the dl_open() functions, I
> > see absolutely *nothing* which would allow me to fetch a
> > class contained inside a .so and call its constructor and
> > methods.
> >    
>
> No. For this, you have to use _one single_ C function which
> can be searched for in dl_open. This C function can
> return a function pointer to a C++ factory method, which itself
> can pass created C++ objects around.
>
> By the way, this is also the method used by Qt itself for its
> plugins. But it is really simple to implement, and there is no
> need to use Qt plugins for this. texmacs itself does not
> need to be linked with Qt.
>
>  
How do you do this with compilers which do not
generate compatible method dispatch code ?

Is there a standard for this (even if it is
only de-facto) ?