[fpc-devel] C++ Linking technology

[Daniël Mantione]

Op Fri, 27 Apr 2007, schreef Michael Van Canneyt:

> On Fri, 27 Apr 2007, ik wrote:
> 
> > On 4/27/07, Daniël Mantione <daniel.mantione at freepascal.org> wrote:
> > >
> > >>
> > >> Op Fri, 27 Apr 2007, schreef Felipe Monteiro de Carvalho:
> > >>
> > >> > Hallo,
> > >> >
> > >> > Another day Florian was talking about the cppclass, a experimental
> > >> > feature to link to c++
> > >> >
> > >> > I would like to know: Could someone inherit a class based on cppclass
> > >> > with only external functions and then add to it it´s own methods and
> > >> > fields?
> > >> >
> > >> > If this doesn´t exist yet, I would say it would be a good adition,
> > >> > because then one can use the c++ classes like they are often used on
> > >> > c++ app: By inheriting them and adding your own code.
> > >> >
> > >> > This is a very specific question, so I could just ask Florian
> > >> > directly, but I guess that here everyone will have access to the
> > >> > answer =)
> > >>
> > >> To be able to support such a thing you would have to implement all
> > >> features of C++ objects into Pascal, effectively turning Pascal into C++
> > >> with a different syntax. The proper way would be to have the C++ class
> > >> implement a Pascal interface, so it can interoperate with Pascal code.
> > >>
> > >
> > >How does other languages such as Perl/Ruby/Python (for example) etc,
> > >handle such connections ?
> 
> They don't have to: the compilers/interpreters for these languages are 
> written in C. All they need to do in the worst case is compile a small 
> stub. For Pascal, the situation is not so simple, as there is no connection
> with C whatsoever.

Some examples:

* C++ constructors do not have a name. Deriving and enhancing 
  C++ classes in Pascal would mean you would have to add syntax to write 
  nameless constructors, and syntax to call a constructor without 
  mentioning its name.

* The copy constructor is a very central theme in C++ OOP programming. 
  Being able to derive from C++ classes would mean you would have to be
  able to write a copy constructor in Pascal, and would modify the 
  semantics of an assignment to call the copy constructor.

To my knowledge, no language has gone this path. Perl, Python all have 
their own OOP classes and deal with C++ only through wrappers.

Daniël