Re: [boost] Alternative solution to intermediate results problem of expression templates.

From: Korcan Hussein (korcan_h_at_[hidden])
Date: 2005-10-24 04:08:31

"Joel de Guzman" <joel_at_[hidden]> wrote in message 
news:djhds4$vvv$1_at_sea.gmane.org...
>
> I didn't run it but I think I understand what's going on. It simply
> encodes the recursive expression-type in the recursive variant.
> There's a significant flaw with this approach: all nodes must
> be known in advance. There is no possibility of user defined leaves;
> nor is there a possibility for having nodes that are from a different
> library;

I relized this when i was reading Spirit's documentation. I did mention from 
the begining all terminal leaf node types must be given, like in an MPL 
sequence (and probably for nonterminal node types if you can add more to the 
set). I did also mention this was in no way been generalized or a library of 
any form it was just an idea i had the other day. It's not true that there 
is "no possibility user-defined leaves" it is just not as simple as erasing 
type.

I had some ideas to get around this, my initial thought was have a fallback 
on to type erasing  you have a catch all type of the set of types in a 
variant that uses type erasing i don't like the idea but in this case there 
would probably be no choice.

So yeah this does not gel so well with Spirit, maybe if boost::variant was 
like OCaml's polymorphic variants it would be a more feasible. Still though 
this could have it uses in other places where client wouldn't normally add 
new internal (nonterminal) nodes.