Re: [boost] [mpl] as_sequence< X< Y > > instantiates typedefs inX<Y >

From: David Abrahams (dave_at_[hidden])
Date: 2005-08-03 06:34:24

Andreas Huber <ahd6974-spamgroupstrap_at_[hidden]> writes:

> David Abrahams <dave <at> boost-consulting.com> writes:
> [snip]
>> > I need to modify that sequence internally. 
>> 
>> You don't mean that, exactly, since all metadata is immutable.
>
> Right, I mean that I can't use e.g. push_front on some sequences.
>
>> > If any sequence was allowed (including immutable ones), I would need
>> > to copy that sequence into an mpl::list<> first. 
>> 
>> Why an mpl::list<>?  What's special about that structurue?  Why not
>> mpl::vector?
>
> The sequence just needs to support certain operations, e.g. push_front, 
> reverse, etc. So, mpl::vector<> should work too (I never checked).

If you're reversing the sequence, all your arguments about requiring
mutability for efficiency reasons are invalid.  You might as well do

   mpl::reverse<user_sequence, back_inserter<vector<> > >
   
> Don't know, I can't think of anything that would keep you from using
> deque or vector. I guess it would be best to document the exact
> requirements and make measurements so that I can tell the user which
> of the standard mpl sequences are best.

Not a bad idea, but I wouldn't go overboard.  In this case the first
priority should be to lift needless restrictions.  The restrictions
you're using don't even neccessarily lead to better efficiency.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com