Re: [boost] Boost.Conversion: functors namming

Subject: Re: [boost] Boost.Conversion: functors namming
From: Vicente Botet (vicente.botet_at_[hidden])
Date: 2011-05-25 07:29:21

Thomas Heller-7 wrote:
> 
> On Wed, May 25, 2011 at 10:44 AM, Vicente Botet
> <vicente.botet_at_[hidden]> wrote:
>>
>> Stewart, Robert wrote:
>>>
>>> Vicente Botet wrote:
>>>> Stewart, Robert wrote:
>>>>
>>>> > Â  Â auto f(factory<short>(_1));
>>>> > Â  Â short const s(f(static_cast<long>(3)));
>>>> >
>>>> > Your suggestions for the "factory" call are:
>>>> >
>>>> > A. boost::make_converter_to<short>(_1)
>>>> > B. boost::conversion::fp::convert_to<short>(_1)
>>>> > C. boost::convert_to<short>(_1)
>>>> >
>>>> > I definitely dislike B. Â A isn't bad, but it should be in the
>>>> > boost::conversion namespace. Â C is very nice, but it should
>>>> > be in the boost::conversion namespace. Â The introduction of
>>>> > the placeholder is enough to signal that the result is a
>>>> > Phoenix lambda.
>>>>
>>>> Even if C is the more elegant, to my taste, it introduce a
>>>> dependency on Boost.Phonix even if functors are not used, and
>>>> this is one thing I would like to avoid. So it seems that A is
>>>> a best compromise.
>>>
>>> That overload can be put into a separate header so it, and its
>>> dependency
>>> on Phoenix, is only visible when desired.
>>> &lt;boost/conversion/functor.hpp&gt;?
>>>
>>>
>>
>> Hi,
>>
>> this independent overloading could be done if there was a class
>> placeholder,
>> but in Phoenix a placeholder is a concept, isn't it. So the overloading
>> can
>> be done only using SFINAE, which implies that one overload works for T
>> that
>> are placeholders and the otherfor T that are no placeholders.
>>
>> Let me know if I'm missing something.
> 
> FWIW, a phoenix actor is a concept, yes. The file
> boost/phoenix/core/is_actor.hpp
> has only a dependency on the boost/mpl/bool.hpp header. So including this
> might
> not really add to much dependency on your code.
> 
> Another possibility certainly is to create your own trait:
> 
> template <typename T, typename Enable>
> struct enable_functor : mpl::false_ {};
> 
> or something, that gets specialized on phoenix::is_actor once your
> user includes the
> header that enables functors. Using this, you gain another point of
> flexibility by being able
> to support other functional style libraries.
> 
> 

Thanks for your clever suggestion. I will adopt it.

Best,
Vicente

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