Re: [boost] [functional] Generic Selector for STL Pair's and Boost.Tuple's

From: Dean Michael Berris (mikhailberis_at_[hidden])
Date: 2007-11-22 10:27:33

On Nov 22, 2007 6:35 AM, Joel de Guzman <joel_at_[hidden]> wrote:
> Dean Michael Berris wrote:
>
> > That being said, the rationale for select<> are the following:
> >
> > 1. It's a generalization of the select1st and select2nd SGI extensions
> > to the STL, intended to work at least with Boost.Tuple's (tr1::tuple
> > ?) and STL Pairs.
> >
> > 2. This is intended to be really simple, and perhaps somehow made
> > self-contained and easy to factor out so that
> >     a) it doesn't pull in Fusion (which I absolutely think is an
> > excellent library, which I fortunately am able to use at work every
> > single day)
> >     b) it only pulls in the required MPL headers, which can even be
> > re-implemented in cases where having the MPL present is unacceptable
> >     c) it only relies on the presence of Boost Tuple (can be made
> > optional by doing some preprocessor checking) and STL pair's
> >
> > So personally, I appreciate the feedback -- it's invaluable feedback
> > at that. But I'd like to be able to make it work by making it
> > self-contained; and if suddenly Joel et al decide to make all Fusion
> > functions (like at_c) be reflected as function objects as well (do I
> > hear Phoenix coming along to contain this? :D), then that's something
> > a lot of people would appreciate as well.
>
> That's a good rationale. I suggest:
>
> 1. write lotsa tests around it
> 2. write it first using fusion
> 3. write it without fusion, making sure all tests pass
> 4. ifdef out fusion and/or mpl code
>     -- give the user a chance to choose. there will be cases when
>        fusion *is* available and your code becomes redundant.
>

This makes sense. I'll do this when I finally find the time. This
usually means weekends for me, so it isn't that far away. ;-)

Curiously, how does one check whether Fusion or MPL is available? Is
there something already available that allows:

#if defined(BOOST_FUSION)
#  include <select/has_fusion.hpp>
#else
#  if defined(BOOST_MPL)
#    include <select/has_mpl.hpp>
#  else
#    include <select/bare.hpp>
#  endif
#endif

?

Pointers would be most appreciated.

Have a good one, and happy holidays to those celebrating!

-- 
Dean Michael C. Berris
Software Engineer, Friendster, Inc.
[http://cplusplus-soup.blogspot.com/]
[mikhailberis_at_[hidden]]
[[phone]]
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