Re: New Ada portable GUI Library?

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Martin Krischik wrote:
> Ludovic Brenta schrieb:
>
> > Martin Krischik wrote:
>
> >> I have another suggestion: A GUI Library based on OpenStep [1].
> > [...]
> >> [1] http://en.wikipedia.org/wiki/OpenStep
> >
> > Do you mean a reimplementation of the OpenStep specification in Ada,
> > or an Ada binding to GNUstep (http://www.gnustep.org) ?
>
> The later. AFAIK GNUStep uses only a small message based dynamically
> typed API with a plain C specification. Qt and Gtk+ use huge OO API's in
> C++ or some kind of strange OO-C.
>
> To make use of that API easier special languages like Objective-C and
> Objective-C++ are used. Those languages can be implemented by a
> preprocessor (currently they are not) so I believe creating an
> Objective-Ada preprocessor should be possible - especially since Ada
> does not use '[' ']' and '@' ;-).

An "Objective-Ada" preprocessor is unnecessary because Ada is already
object-oriented, and now even has interfaces similar to Objective-C's
protocols. Therefore, one would only need a binding generator that
would produce Ada specifications with pragma Import statements from
Objective-C specifications. Of course, such a binding generator would
have to know how the particular Objective-C compiler mangles names.

The stumbling blocks would be to implement Objective-C's reflection,
dynamic typing and garbage collection in Ada. In particular,
reflection and dynamic typing are alien to Ada's philosophy.

> We would not be the first: Google-ing shows that Objective-TCL [1],
> Objective-Perl [2] already exists and Objective-Cobol and
> Objective-Fortran are rumoured [3] - even talk about Objective-Ada isn't
> new [3].

That was before Ada 95 added tagged types.

> The advantage is that once we have an preprocessor the hole library
> becomes available. That's unlike Gtk or Qt where we have to write a
> separate binding for each class we want to use and where - forever - we
> will be hobbling behind.

I don't think the preprocessor you speak of would solve anything; the
binding generator might but beware of the stumbling blocks I
mentioned.

> > The latter
> > would require both the Ada and Objective-C runtime libraries...
>
> Indeed - but that is not different from Gtk+ and Qt approach. And bare
> metal is only feasible for Windows but not for X11.

OK, Qt requires a C++ runtime like GNUstep requires an Objective-C
runtime. However, GTK+ only requires the C runtime and that's
intentional: one of the design goals of GTK+ from the onset is to
facilitate bindings to other languages.

--
Ludovic Brenta.