[boost] Re: Request for mpl::empty_sequence

From: Alexander Nasonov (alnsn-mycop_at_[hidden])
Date: 2004-04-29 13:54:42

Aleksey Gurtovoy wrote:

> Alexander Nasonov writes:
>> For the purpose of forward declaration of class templates this read-only
>> lightweight sequence might be useful. For example, one might declare
>> class template Selector in fwd file:
>> 
>> // empty_sequence.hpp is designed for inclusion into fwd files
>> #include <boost/mpl/empty_sequence.hpp>
>> 
>> template<class Variants = empty_sequence>
>> class Selector;
> 
> Seems like a reasonable wish, somewhat correlating with 'single_view'
> (http://tinyurl.com/yqfp2). Why don't you write up the docs for it, and
> I'll put it in? A reference page template attached.

Ok. I'll do it.

>> This is not yet complete. I hope that support for some transformations
>> will be added later (transformation doesn't change empty_sequence unless
>> the size is changed)
> 
> I am afraid I don't understand this part.

I was trying to say that the following doesn't work
transform_view<empty_sequence, add_pointer<_1> >.

Any transformation that doesn't change the size of empty_sequence is
certainly a trivial transformation. Why not allow it to compile?
If I understand MPL philosophy correctly it's enough to add clear_traits
specialization.

-- 
Alexander Nasonov
Independent Developer and Consultant