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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Can ADA95 inherit from C++ classes
Date: 1997/09/19
Message-ID: <dewar.874680076@merv>#1/1
X-Deja-AN: 273895354
References: <5vltvf$q1m$1@news.cc.ucf.edu> <34212D90.318E@gsfc.nasa.gov>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-09-19T00:00:00+00:00
List-Id: <comp.lang.ada>


Stephen said

<<In another response I said ObjectAda could do this. That's wrong;
ObjectAda can _import_ C++ classes as packages, but it cannot _inherit_
from C++ classes. Sorry for the misunderstanding.>>

Just to make sure that things are clear, GNAT *can* import C++ classes,
including multiply inherited classes from C++, treat them as tagged
types, extend them with new primitive operations, and pass the resulting
tagged type back to C++ to be treated as an extended class.

However, this is a complex mechanism, and has to be tailored to a particular
C++ compiler, since it obviously depends on Ada and C++ using identical
data structures for the objects. This tailoring is done by modifying the
body, and possibly the private part of the package Interfaces.CPP.

Furthermore, to use the interfacing capability, a rather complex set of
pragmas is required. These pragmas can be generated by hand, but it is a
tricky process. SGI has a binding generator that automatically generates
these pragmas for their Delta C++ technology compiler used together with
GNAT.

People have experimented successfully with example bindings to C++ in
other environments (e.g. Microsoft C++), but for this feature to be
fully usable, a binding generator is most desirable. 

Such a binding generator is not a trivial tool, since it needs full
understanding of the C++ sources, and must therefore be built around
a C++ front end. Ada Core Technologies hopes to introduce a binding
generator capable of handling this problem some time in the future, but
there is no definite schedule for this work.

Meanwhile, it is most certainly possible to import C++ classes as packages,
if necessary by using a C wrapper to ensure maximum portability.