Re: [boost] [local] Review (and resignation from review assistant)

Subject: Re: [boost] [local] Review (and resignation from review assistant)
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2011-11-21 10:33:20

On 11/21/2011 09:31 AM, Lorenzo Caminiti wrote:
> On Mon, Nov 21, 2011 at 9:56 AM, Joel de Guzman
> <joel_at_[hidden]>  wrote:
>> On 11/21/2011 10:41 PM, Andrzej Krzemienski wrote:
>>>>> - What is your evaluation of the design?
>>>
>>>> The library is very well designed.  The function declaration syntax looks
>>> a little foreign at first, but it is very easy to get used to.
>>>   Furthermore, error messages are usually able to point you to what you did
>>> wrong.  The fact that you can write the body of the function in plain C++
>>> code is a major advantage of this library.  Some have referred to
>>> Boost.Bind, Boost.Lambda and Boost.Phoenix as essentially being equivalent
>>> to this library, but in none of those libraries can you express the body of
>>> your function in plain C++;  one advantage of this is that errors in your
>>> code result in normal C++ error messages rather than cryptic error messages.
>>>
>>> Lorenzo, given this comment by Greg, I do have one more suggestion for
>>> documentation (or did someone already say it?). Given the heated discussion
>>> of whether Boost.Bind, Boost.Lambda and Boost.Phoenix are sufficient to
>>> render Boost.Local unnecessary, perhaps it would be worth to provide a
>>> comparison of how my code (not too trivial, and not too complex) would look
>>> in either case. For instance:
>>>
>>>
>>> With C++11 lambdas:
>>>
>>> for_each( vec.begin(), vec.end(), []( std::string&  n ){ if(n.empty()) n =
>>> "n/a";} );
>>>
>>>
>>> With Boost.Lambda + Boost.Bind:
>>>
>>> for_each( vec.begin(), vec.end(), if_then(boost::bind(&std::string::empty,
>>> _1), _1 = "n/a") );
>>>
>>>
>>> With Phoenix:
>>>
>>> using boost::phoenix::arg_names::arg1;
>>> using boost::phoenix::if_;
>>> using boost::phoenix::bind; // right?
>>>
>>> for_each( vec.begin(), vec.end(), if_(bind(&std::string::empty, arg1)) [
>>> arg1 = "n/a" ] );
>>
>> Better:
>>
>>   for_each( vec.begin(), vec.end(), if_(empty(_1)) [_1 = "n/a" ] );
>>
>>> With Boost.Local (Boost.Closure):
>>>
>>> BOOST_CLOSURE_PARAMS( std::string&  n ) {
>>>      if( n.empty() ) n = "n/a";
>>> }BOOST_CLOSURE_NAME(replace_empties);
>>>
>>> for_each( vec.begin(), vec.end(), replace_empties );
>>>
>>>
>>> Ok, I am not sure if there are no better ways to write it in each variant,
>>> and I may be biased. I also didn't try to compile the examples. But it
>>> should give the potential users an overview of options they have.
>>
>> Yep. This highlights the verbosity well:
>>
>>   for_each( vec.begin(), vec.end(), if_(empty(_1)) [_1 = "n/a"] );
>>
>> vs:
>>
>>   BOOST_CLOSURE_PARAMS( std::string&  n ) {
>>     if( n.empty() ) n = "n/a";
>>   }BOOST_CLOSURE_NAME(replace_empties);
>>
>>   for_each( vec.begin(), vec.end(), replace_empties );
>
> IMO, I'd be better if the example had more than 1-line of code in its
> body. In the docs, I have an example to show the different approaches
> that has 2-lines and I'd still think more than 2 statements would be
> better:
>
> https://svn.boost.org/svn/boost/sandbox/local/libs/local/doc/html/boost_local/Alternatives.html#boost_local.Alternatives.local_functions.examples
>
> C++11 lambdas:
>
>      std::for_each(v.begin(), v.end(), [&sum, factor](double num) {
>          sum += factor * num;
>          std::cout<<  "Summed: "<<  sum<<  std::endl;
>      });
>
> Boost.Local:
>
>      void BOOST_LOCAL_FUNCTION_PARAMS(double num,
>              bind&  sum, const bind&  factor) {
>          sum += factor * num;
>          std::cout<<  "Summed: "<<  sum<<  std::endl;
>      } BOOST_LOCAL_FUNCTION_NAME(add)
>      std::for_each(v.begin(), v.end(), add);
>
> Boost.Phoenix:
>
>      std::for_each(v.begin(), v.end(), let(_f = cref(factor))[
>          ref(sum) += _f * _1,
>          std::cout<<  val("Summed: ")<<  ref(sum)<<  "\n"
>      ]);

Why not just:
       std::for_each(v.begin(), v.end(),
           ref(sum) += cref(factor) * _1,
           std::cout<<  val("Summed: ")<<  ref(sum)<<  "\n"
       );

> HTH,
> --Lorenzo
>
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