Re: [boost] [Fusion] Heads up

From: David Abrahams (dave_at_[hidden])
Date: 2006-09-01 06:43:02

Joel de Guzman <joel_at_[hidden]> writes:

> David Abrahams wrote:
>> Joel de Guzman <joel_at_[hidden]> writes:
>> 
>>> There's also an interesting
>>> use-case that became apparent recently: making arbitrary structs/classes
>>> conforming sequences easily-- as easy as providing a single function.
>>> Pardon me if this is rather sketchy at this point, but imagine
>>> being able to write:
>>>
>>> Our user defined struct:
>>>
>>>      struct point { float x, float y; };
>>>
>>> Customization:
>>>
>>>      fusion::map<keys::x_, keys::y_, float&, float&>
>>>      as_fusion_sequence(point& p)
>>>      {
>>>          return fusion::map_tie<keys::x_, keys::y_>(p.x, p.y);
>>>      }
>>>
>>> Use:
>>>
>>>      point p = { 123.456, 789.012 };
>>>      fusion::for_each(p, std::cout << _1 << std::endl);
>> 
>> That's nice, but I don't think it's really the same thing.  Doesn't it
>> incur an extra level of indirection?
>
> Not the same as what? Sorry, I think I missed something in
> your question/comment.

It's not really the same as making point actually *be* a conforming
fusion sequence, in some sense, is it?  You've sorta "cheated" by
giving it a kind of implicitly-recognized conversion into a view.

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