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Subject: Re: [boost] [GSOC] Mentors for a C++11 TMP-related project
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2014-03-09 15:52:26

On 9 Mar 2014 at 13:01, Louis Dionne wrote:

> > I haven't looked at your MPL11 replacement library closely enough to
> > say whether it's a good replacement for MPL. My personal single
> > biggest concern is that I think you need Concepts in the language
> > before an MPL replacement can really fly, and that probably removes
> > Visual Studio from available compilers which is a showstopper. I
> > certainly am looking forward hugely to your C++ Now presentation to
> > learn more.
> May I ask why would Concepts be necessary for a "new MPL"? Do you have
> anything more specific in mind? I would like to know because that might
> influence my current work.

It's purely a gut feeling, not based in any fact. And let me clarify,
by Concepts I specifically mean Andrew Sutton's Concepts Lite which
is now heading into the standard.

Andrew's Concepts Lite let you much more richly specify partial
template specialisations - in fact, PTS looks very clunky compared to
what Concepts Lite allows. That certainly helps with the brevity and
power of implementation, but it also helps with the sanity of usage.
Whilst use of the existing MPL is fairly problem free, that is
definitely not the case for stuff which is based on the MPL where
you'll find the metaprogramming becomes very brittle a la
Boost.Spirit. I suspect, without evidence, that correctly and
permanently eliminating that brittleness will require Concepts Lite
in the MPL layer, not in the layer above.

I stress it's a gut feeling. I have no evidence, and am hoping your
C++ Now presentation might illuminate things for me.


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