Re: [boost] If boost::fusion is the hammer, then what's the nail?

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2006-12-14 09:52:04

John Maddock wrote:
> Weapon Liu wrote:
> 
>>I personally very like this fancy facility, and that's why I present
>>these mumbles here to annoy you guys( if so, my apologies go here:-))
>>Any comments?
> 
> 
> I can give you one use I have for tuples:

> I've also used tuples in place of struct's whenever I have an API that needs 
> to return more than 2 items.  For example I have some root finding 
> algorithms that accept a unary functor whose root is to be found: the 
> functor returns a tuple containing the function evaluation, plus the first 
> two derivatives.  Using a tuple here simplified both implementation and 
> documentation. 

I have used tuples in a similar manner, but I kinda think its not the 
best to do; a named tuple would be more appropriate, or maybe just a struct.

What bothers me is the self-explanatory properties are lost; I can't 
figure out what tuple element that means what by just looking at the 
code. Is it

   tie(eval,dev1,dev2) = find_root(...)

or

   tie(dev1,dev2,eval) = find_root(...)

?

Instead a struct would be somewhat unambiguous:

   template< class Float >
   struct root_result
   {
     Float eval, dev1, dev2;
   };

   root_result<float> r = find_root( ... );

-Thorsten