[boost] Re: enable_if review

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2003-10-12 06:32:06

David Abrahams wrote:
> Daniel Frey <daniel.frey_at_[hidden]> writes:
> 
>>smallest issue, I think the separation of components (with separate
>>documentation!) is much more important. Having template-traits is
>>nice, but when they are hidden inside MPL and not documented, they
>>are close to useless for me. 
> 
> But Aleksey didn't consider it part of MPL's charter to provide that
> in a way that you could use it.

Of course, I guess the MPL was already enough work in its current form :)

> Likewise, I have indirect_traits.hpp
> in boost/python/detail, with things like is_reference_to_constant.  If
> someone else is willing to go to the effort to factor it out, document
> it and take it through (mini) review, then everyone else can use it.
> Otherwise, and until then, it remains hidden.

Depending on my time, I might try to do that. But there are other things 
to do before that :)

>>Look at the history of enable_if: It was developed several times
>>independently IIUC and just now we are giving it the attention it
>>deserves as a valuable technique on it's own. 
> 
> Not quite; it was developed once by Jaakko et al (**); they wrote a
> paper on it, and people implemented their technique several times in
> Boost.

I wasn't clear on that, sorry. I meant the implementation, not the 
technique itself. We already known that besides the basic technique 
there's usually a bunch of work-arounds needed for various compilers. A 
single implementation helps to cope with that and scales better than 
independent implementations.

> Oh, and BTW, I'm not advocating sticking enable_if into MPL.

I think that even Gennadiy just asked whether it makes sense instead of 
advocating for it strongly. Seems we all agree on that point :)

> At the same time, if a library author needs a component to get his job
> done, and writes it, he shouldn't feel compelled to put that component
> through a separate review if it's not part of his mission.  Template
> traits or whatever you're calling them falls into that category.

I understand that you want to prevent further burdon on the authors, but 
I am already content if they at least consider factoring out generally 
useful parts. OK, enough bandwidth wasted. :)

Regards, Daniel

-- 
Daniel Frey
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