[boost] Re: Formal Review: FOREACH macro

From: Arkadiy Vertleyb (vertleyb_at_[hidden])
Date: 2005-05-09 09:19:50

"David Abrahams" <dave_at_[hidden]> wrote

> "Andrei Alexandrescu (See Website For Email)"
<SeeWebsiteForEmail_at_[hidden]> writes:
> > 1. Start from the Boost implementation of the C++ preprocessor, and
> > add sane features to it. Keep the old preprocessor features as
> > deprecated.
>
> That one's a possibility.  I personally would not want to solve these
> problems in the preprocessor layer because I want better integration
> with the rest of the language than that approach can offer.  Others
> may feel differently, of course.

A better integration is not necessarily a good thing -- it's too
restrictive.  Something like FOREACH, for example (let's pay a tribute to
the subject of this discussion), would not be possible in a well-integrated
system -- the piece of code it generates is not, by itself, a valid fragment
of a C++ program.  So a totally independent code generation layer does have
its advantages (at least it's more flexible).

> > 3. Start an effort to add ways of manipulating ASTs to the native
> > language so as to eliminate the need for preprocessing.
>
> That approach has promise.  Bjarne has a project to standardize a C++
> program representation and manipulation library -- it could be
> interesting to build a metaprogramming system around that.

Well, of course, ultimately it should bring us to something like this, so
that we would not have to, for example, instantiate a function template, and
take its sizeof() just in order to figure out if one class is derived from
another.  IMO, it applies to template metaprogramming even more then to PP.

I am not too optimistic about this happenning in the near future, though.

Regards,
Arkadiy