[boost] Re: ATTN: All Developers Interested in Boost.Preprocessor

From: Vesa Karvonen (vesa_karvonen_at_[hidden])
Date: 2003-04-14 07:17:23

Paul Mensonides:
[...]
>I need input regarding the paper itself and anything that should be
>added or subtracted from the paper.
[...]

It looks quite reasonable and very conservative to me.

It is difficult to imagine a really good reason not to adopt the C99 
preprocessor extensions into C++.

Well-defined token-pasting is also reasonable.

The way I see it, the module system is the only real extension - and the 
most difficult to justify. The way I understand it, the module system 
doesn't make the macro system much safer for macro users. It probably makes 
macros safer for users of ordinary libraries (who don't want to care about 
the macros). (The C preprocessor is nowhere near as safe as the hygienic 
(and mostly hygienic) macros of Scheme, for instance.)

I think that it would not necessarily be wise to use lowercase names for 
macros even with the module system. The problem is that within a module, you 
could still get all sorts of nasty surprises if you forget that you have 
imported a particular macro (a few hundred lines above). (Contrast this with 
Scheme hygienic macros, where ordinary bindings can shadow syntactic 
bindings and vice versa. In addition, hygienic macros in Scheme are also 
referentially transparent - not unlike templates in C++.)

Also, the syntax for referring to macros, e.g.

  BOOST::QUALIFIED

seems quite ambiquous to me. It looks like three separate tokens. Has 
someone implemented a module system that uses this syntax?

-Vesa

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