Tobias Schwinger wrote:
2. Fusion and MPL placeholder expressions
MPL placeholder expressions are very convenient for specifying the result because of their lazy nature (see lines 267, 312). Of course, this approach trades compile time for syntactic sugar. The syntactic sugar might not be entirely irrelevant, because it allows us to emphasize even complex problems with little code.
Sure.
So, I still wonder, whether it is a good idea to use MPL lambda for the result computation or not. Is it?
I think so, yes.
If so (even occasionanlly), it would be necessary to have at least accessors for pair members (they are needed to keep the evaluation lazy, see line 211) or, ideally, if there would be a normalization between the STL and the MPL pair concepts (then MPL's accessors, 'first' and 'second', could be borrowed).
If my suggestion to make mpl/fusion pair fully conforming mpl/fusion sequences is accepted, then you can use code like mpl::begin<_> or mpl::at<_, N>.
(It would also be cool if one could just typedef the lambda expression to nested result or inherit from a wrapper. I don't know whether it's possible and a good idea - this part is just loud thinking)...
Hmmm... can you elaborate. I lost you here. Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net