Re: [boost] [TTI] Review

Subject: Re: [boost] [TTI] Review
From: lcaminiti (lorcaminiti_at_[hidden])
Date: 2011-07-11 18:25:13

Edward Diener-3 wrote:
> 
> On 7/11/2011 5:02 PM, lcaminiti wrote:
>>
>> Edward Diener-3 wrote:
>>>
>>> On 7/11/2011 2:45 PM, Joel falcou wrote:
>>>> See :
>>>>
>>>> https://github.com/MetaScale/nt2/blob/master/modules/sdk/include/nt2/sdk/details/preprocessor.hpp
>>>>
>>>>
>>>>
>>>> for the file, line 85 and after.
>>>>
>>>> The point is it works without variadics
>>>
>>> Line 87: #define NT2_PP_DETAILS_STRIP_PARENS_I(...) 1,1
>>> Line 91: #define NT2_PP_DETAILS_TEST_ARITY_I(a,b,c,...) c
>>> Line 96: #define NT2_PP_DETAILS_MAYBE_STRIP_PARENS_2_I(...) __VA_ARGS__
>>>
>>> Clearly it needs variadic macro support.
>>>
>>> I have already added a REMOVE_PARENS ( the equivalent to NT2_PP_STRIP(X)
>>> in your URL above ) to a proposed addition to pp-lib which I am
>>> discussing with Paul Mensonides, based on the updated variadic macro
>>> support on which both of us worked and which is now in the Boost trunk.
>>>
>>> My point is also that I may well be able to simplify the
>>> BOOST_TTI_TEMPLATE macros in TTI using variadic macro support
>>> techniques, as Lorenzo suggested, but I do not feel correct in dropping
>>> macro support support for compilers which do not support variadic macros
>>> although I understand there are few of them left.
>>>
>>
>> I will later reply to all your comments on my review but let me quickly
>> clarify a couple of things.
>>
>> My suggestion was to have the *same* macro TTI_TEMPLATE handle *both*
>> variadics tupletes and sequences.
> 
> I did understand it, and I am willing to do that, but of course it needs 
> variadic macro support in the compiler. But what do you think I should 
> do if the compiler does not support variadic macros ? The possibilities
> are:
> 

I was trying to say for compilers without variaidics (detected by
BOOST_NO_VARIADIC_MACROS) you can do:

    TTI_TEMPLATE(trait, [tpl_signature_seq_ {class | struct}] name)

And for compilers with variadics you can do:

    TTI_TEMPLATE(trait, [{tpl_signature_seq_ | tpl_signature_va_} {class |
struct}] name)

Can't you? (Am I missing something?)

> 1) All compilers for which TTI will compile correctly support variadic 
> macros so don't worry about it and do nothing.
> 
> 2) If the compiler does not support variadic macros, then the particular 
> BOOS_TTI_TEMPLATE macro and functionality can not be used, and this 
> needs to be documented.
> 
> 3) Along with the the variadic version of BOOST_TTI_TEMPLATE which you 
> suggested, and which in agreeing with you I can indeed implement and 
> have decided to so do ( thanks for the good suggestion ), I will still 
> need separate versions of BOOST_TTI_TEMPLATE and 
> BOOST_TTI_TEMPLATE_CHECK_PARAMS for compilers which do not support 
> variadic macros, possibly with slightly different names.
> 
> Now you may feel that 1) or 2) are the right ways to look at things, but 
> I am obliged to do 3) even if it adds another macro name ( or two ) for 
> compilers which do not support variadic macros. This still means that I 
> will do as you have suggested for compilers which do support variadic 
> macros. So I hope my choice of 3) satisfies you while still supporting 
> the rare compiler user when variadic macros are not supported.
> 
> Also please remember that while most compilers support variadic macros, 
> some of them need a compiler switch to be turned on to do so properly, 
> and there are programmers who may not want to use that compiler switch.
> 
>> The pp skeleton code will go something
>> like:
>>
>> #if VARIADICS
>>
>> #define TTI_TEMPLATE_VA_(...) \
>>      TTI_TEMPLATE_SEQ_(VA_TUPLE_TO_SEQ(__VA_ARGS__))
>>
>> #define TTI_TEMPLATE(...) \
>>      BOOST_PP_IIF(IS_VARIADIC(__VA_ARGS__), \
>>          TTI_TEMPLATE_VA_ \
>>      , \
>>          TTI_TEMPLATE_SEQ_ \
>>      )(__VA_ARGS__)
>>
>> #else // variadics
>>
>> #define TTI_TEMPLATE(seq) TTI_TEMPLATE_SEQ_(seq)
>>
>> #endif // variadics
>>
>> Take a look at BOOST_LOCAL_FUNCTION_PARAMS at:
>> http://svn.boost.org/svn/boost/sandbox/local/boost/local/function.hpp
>>
>> This macro could be expanded to also detect a single token and accept the
>> trait parameters in front. The full grammar will then read something
>> like:
>>
>> TTI_TEMPLATE(trait, [tpl_signature_ {class | struct }] name)
>>
>> If the compiler supports variadics:
>>
>> tpl_signature_:
>>      tpl_signature_va_ | tpl_signature_seq_ // you can use either
>> variadics
>> or sequences :)
>>
>> If not:
>>
>> tpl_signature_:
>>      tpl_signature_seq_ // you must use sequences (because variadiacs are
>> not
>> supported)
>>
>> Where:
>>
>> tpl_signature_seq_:
>>      template( (class | typename | type_identifier | tpl_signature_seq_)
>> ...
>> ) // the pp-seq
>>
>> tpl_signature_va_:
>>      template<  {class | typename | type_identifier | tpl_signature_seq_}
>> ...
>>> // the pp-variadic tuple
>>
>> Where lexical conventions are:
>>      [token] := token is optional
>>      token1 | token 2 := either token1 or token2
>>      {expr} := the token(s) resulting from the inner expression epxr
>>      (tokens) ... := repeat tokens within parenthesis one or more times
>> (tokens) (tokens) etc
>>      tokens ... := repeat tokens separated by commas one or more times
>> tokens, tokens etc
>>
>> I think this should be possible but usually the devil is in the
>> details...
>> so I don't know unless someone tries to implement it :)
>>
>> The real question still stands: Would this be a better interface for
>> TTI_TEMPLATE? (You know my opinion is yes, but that's just my opinion.)
>>
>> Please ask questions and let me know if I am not able to explain myself.
> 
> I appreciate the code, and logic, but I can work it out for myself. My 
> experience working with Paul Mensonides on variadic macro support for 
> pp-lib has made me a much better macro coder using pp-lib, and I have 
> learned nearly all the good 'tricks'.
> 

Sure. BTW, if you end-up taking a look at Boost.Local and see strange
things, please let me know (I'm happy to improve/fix my code if needed).

Thanks,
--Lorenzo

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