Re: [boost] [functors] proposal

Subject: Re: [boost] [functors] proposal
From: Piotr Wygocki (vwygos_at_[hidden])
Date: 2013-10-23 08:02:25

On 23 October 2013 13:21, Vicente J. Botet Escriba <vicente.botet_at_[hidden]
> wrote:

> Le 23/10/13 13:10, Piotr Wygocki a écrit :
>
>  Than you for your feedback!
>>
>>
>>
>>  Are you aware of Boost.Phoenix ( or its predecessor Boost.Lambda ) ? Also
>>> some of the functors appear to duplicate functors in the C++ standard
>>> library in functional.
>>>
>>
>> 1) This is good point, this functors are for this kind of people who like
>> lambdas.
>>
>>   Many of proposed functors are equivalent to very simple lambdas.
>>   For example:
>>      ArrayToFunction can be replaced in most cases replaced with
>>
>>     auto arrayToFunction = [&](int i){ return v[i];};
>>
>> or
>>
>>    auto arrayToFunction = phoenix::ref(v)[_1];
>>
>>    In this case my proposal is to standarize this kind of popular usage:
>>    auto arrayToFunction = make_ArrayToFunctor(v);
>>
> Popularity is subjective.

Sure. I chose functors which are popular in MY opinion.
I think you agree that "Less" is popular.

>  2) There is another use case for people who like passing functors and need
>> default arguments.
>>
>>   For example my SkipFunctor does exactly the same job as
>> phoenix::nothing.
>>   For example my RetrunFalseFunctor does exactly the same job as
>> phoenix::val(true).
>>
>>   Look at this use case:
>>
>>   template <typename SomeAction =  SkipFunctor, typename StopCondidtion =
>> ReturnFalseFunctor>
>>   struct Algorithm {
>>
>>   };
>>
>>   AFAIK it cannot be replaced with phoenix construction because we do not
>> have the type of the nothing functor.
>>   Particularly, note that decltype(phoenix::nothing) is not going to work.
>>
>>   This is tiny difference but this play a big role in a code I write.
>>
>>  What about adding phoenix::true_/phoenix::false_**?
>

I don't get it. Could you be more specific?

I'd like to reestablish my use case. My previous post was messy (sorry!).
We've got a class which can be modified by some functors.
This functors have default values:

  template <typename SomeAction =  SkipFunctor, typename StopCondidtion
=ReturnFalseFunctor>
  struct Algorithm {
      Algorithm(SomeAction action = SomeAction(), StopCondidtion =
StopCondition());

  };

Could you solve this using constructions from phoenix?
The second question is of course: is this a good design?

Regards,

Piotr

>>
>>  Vicente
>
>
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