Re: [Boost-users] [fusion] const and transform algorithm

Subject: Re: [Boost-users] [fusion] const and transform algorithm
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2009-01-07 01:29:51

----- Original Message ----- 
From: "Joel de Guzman" <joel_at_[hidden]>
To: <boost-users_at_[hidden]>
Sent: Wednesday, January 07, 2009 1:58 AM
Subject: Re: [Boost-users] [fusion] const and transform algorithm

> 
> vicente.botet wrote:
>> ----- Original Message ----- From: "Joel de Guzman"
>> <joel_at_[hidden]> To: <boost-users_at_[hidden]> Sent: Tuesday,
>> January 06, 2009 11:26 PM Subject: Re: [Boost-users] [fusion] const and
>> transform algorithm
>> 
>> 
>>> vicente.botet wrote:
>>>> Hi,
>>>> 
>>>> What is the reason fusion::transform taskes a const Sequence? template< 
>>>> typename Sequence, typename F
>>>>> 
>>>> typename result_of::transform<Sequence const, F>::type transform( 
>>>> Sequence const& seq, F f);
>>>> 
>>>> Does this means that the transform do not change the sequence itself o
>>>> also its elements?
>>> Yes. Fusion transform returns a lazy (transform) view. This view is
>>> non-mutating. It is not like STL's transform which mutates the target
>>> container in place. Fusion's is purely functional and lazily evaluated.
>> 
>> Can for_each mutate the sequence elements? 
> 
> Yes.
> 
> if yes, would the following get a
>> transformation I'm locking for?
> 
> I don't know. I'm not sure what you are looking for.

I just wat to apply the unction get to a tuple of futures and reviver the stored values. 
T& future<T>::get() is non const

>>> vector<int, char> v; v = transform(v, f);
>> 
>> I was lock for in the documentation and I have not found this assignation.
>> Where in the documentation can I found that I can do that?
> 
> See the sequence/views concepts and the docs for the containers.
> For example (http://tinyurl.com/84vdvp):
> 
> Notation:
> v Instance of vector
> s A Forward Sequence
> 
> Expression Semantics:
>  v =  s  Assigns to a vector, v, from a Forward Sequence, s.

Thanks for the reference. I was looking for a function prototype. BTW, the example is not in line with the functions.
vector<int, float> v(12, 5.5f);
std::cout << at_c<0>(v) << std::endl;
std::cout << at_c<1>(v) << std::endl;
 
>> If for_each can change/mutate the sequence itself, why don't have a
>> mutating_transform that takes a Sequence& and not a Sequence const&
> 
> Because it is not needed.
> 
>> Just a last question. How move semantics maps with purely functional
>> Sequences? Do you plan to add move semantics for the elements of the tuple?
>> The concept of MovableSequence has a sens for you?
> 
> Makes sense. Last BoostCon, we had a workshop about implementing
> Fusion for 0x incuding move. We'll have it when it is available.

Great! Would you try with a Boost.Move library?

Thanks,
Vicente