Re: [boost] [preprocessor] Variadics suggestion

Subject: Re: [boost] [preprocessor] Variadics suggestion
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-10-09 21:07:44

on Fri Oct 05 2012, Paul Mensonides <pmenso57-AT-comcast.net> wrote:

> On Thu, 04 Oct 2012 21:31:48 -0400, Dave Abrahams wrote:
>
>> on Wed Sep 26 2012, Paul Mensonides <pmenso57-AT-comcast.net> wrote:
>> 
>>> Right, and what will change that sad fact?  Attempting to workaround
>>> forever isn't working.  Similarly, is the whole world supposed to not
>>> use variadic templates because VC++ doesn't implement them?  At least
>>> that's likely to change, but a line needs to be drawn.  It is one thing
>>> for a workaround to be an implementation detail.  It is another when it
>>> affects the interface.  In the latter case, IMO, the best thing to do
>>> is provide the interface that *should* exist and either not support the
>>> compilers that don't work or provide some clunkier interface for those
>>> compilers. Doing else cripples technological advancement.
>> 
>> I'll mention again that I think we should accept some libraries that
>> won't work on broken compilers (like Chaos).  "Boost works on this
>> compiler" is an important selling point.
>
> 1) How is the modularization/git transition going?

I think
https://groups.google.com/forum/?fromgroups=#!topic/ryppl-dev/12z1ahWsNtk
contains the best answers to that question so far.  Short answer: quite
well; we just need to keep moving it forward.

> 2) For a macro library, do we still need to have a BOOST_ prefix or could 
> I just keep the CHAOS_PP_ prefix?  I cannot use BOOST_PP_ without bending 
> over backwards to find contrived names for everything, and the namespace 
> of brief names beginning with BOOST_ is tiny--especially when a library 
> provides hundreds of user-interface (i.e. not implementation detail 
> macros).

I don't have a strong position on this one, but will point out that
there are other options such as BOOST_CHAOS_ or BOOST_CPP_

> A quick example:
>
> #include <chaos/preprocessor/arithmetic/dec.h>
> #include <chaos/preprocessor/control/if.h>
> #include <chaos/preprocessor/facilities/empty.h>
> #include <chaos/preprocessor/punctuation/comma.h>
> #include <chaos/preprocessor/recursion/basic.h>
> #include <chaos/preprocessor/recursion/expr.h>
> #include <chaos/preprocessor/tuple/eat.h>
>
> // interface:
>
> #define DELINEATE(c, sep, m, ...) \
>     DELINEATE_S(CHAOS_PP_STATE(), c, sep, m, __VA_ARGS__) \
>     /**/
> #define DELINEATE_S(s, c, sep, m, ...) \
>     DELINEATE_I(s, c, CHAOS_PP_EMPTY, sep, m, __VA_ARGS__) \
>     /**/
>
> // implementation:
>
> #define DELINEATE_I(s, c, s1, s2, m, ...) \
>     CHAOS_PP_IF(c)( \
>         DELINEATE_II, CHAOS_PP_EAT \
>     )(CHAOS_PP_OBSTRUCT(), CHAOS_PP_NEXT(s), \
>         CHAOS_PP_DEC(c), s1, s2, m, __VA_ARGS__) \
>     /**/
> #define DELINEATE_INDIRECT() DELINEATE_I
> #define DELINEATE_II(_, s, c, s1, s2, m, ...) \
>     CHAOS_PP_EXPR_S _(s)(DELINEATE_INDIRECT _()( \
>         s, c, s2, s2, m, __VA_ARGS__ \
>     )) \
>     m _(s, c, __VA_ARGS__) s1() \
>     /**/
>
> // reusable:
>
> #define REPEAT(c, m, ...) DELINEATE(c, CHAOS_PP_EMPTY, m, __VA_ARGS__)
> #define REPEAT_S(s, c, m, ...) \
>     DELINEATE_S(s, c, CHAOS_PP_EMPTY, m, __VA_ARGS__) \
>     /**/

What's the point of showing REPEAT here?  It doesn't seem to be used
below.  Are you just illustrating that you can build REPEAT and ENUM
using the same foundation?

> #define ENUM(c, m, ...) DELINEATE(c, CHAOS_PP_COMMA, m, __VA_ARGS__)
> #define ENUM_S(s, c, m, ...) \
>     DELINEATE_S(s, c, CHAOS_PP_COMMA, m, __VA_ARGS__) \
>     /**/
>
> // recursive:
>
> #define TTP(s, n, id) \
>     template<CHAOS_PP_EXPR(ENUM( \
>         CHAOS_PP_INC(n), class CHAOS_PP_EAT, ~ \

Did CHAOS_PP_INC come in with CHAOS_PP_DEC?  I don't see an #include for
it.

>     ))> class id ## n \
>     /**/
>
> CHAOS_PP_EXPR(ENUM(3, TTP, T))
>
> -> template<class> class T0 ,
>     template<class, class> class T1 ,
>      template<class, class, class> class T2
>
> Complicated?...yes.  But compare that to the implementation of 
> BOOST_PP_REPEAT.  Unlike BOOST_PP_REPEAT, however, this macro can be 
> recursively reentered about 500 times.  The actual implementations of 
> these in Chaos is far fancier.

I went to look at the code and found the mercurial repo doesn't appear
to contain most of chaos, which was a little confusing.  Just thought it
would be worth telling people to look at the CVS.

-- 
Dave Abrahams
BoostPro Computing                  Software Development        Training
http://www.boostpro.com             Clang/LLVM/EDG Compilers  C++  Boost