Re: [Boost-users] Odd limitation in Fusion design ?

Subject: Re: [Boost-users] Odd limitation in Fusion design ?
From: Larry Evans (cppljevans_at_[hidden])
Date: 2010-07-07 21:26:46

On 07/07/10 19:40, John Dlugosz wrote:

 > I see that the "Cons" sequence is Forward-only.  reverse_view
 > requires a Bidirectional sequence, at least.  The for_each iteration
 > function goes forward.

 > However, hand-written recursive loop on a cons-like thing can do
 > stuff before and other stuff after the recursive call to the cdr
 > portion.  Putting stuff "after" will give a reversed processing.
 > So, in general, a reversed_for_each is not out of the question, and
 > can be specialized for Cons when the general form of iterating
 > backwards does not work.
 >

 > I also ponder that a more general form that indeed does stuff before
 > AND other stuff after recursing the tail would be a useful addition.
 > It might actually perform one operation iterating forward, then
 > perform the other operation iterating backward back to the
 > beginning; or use recursion; depending on the nature of the
 > container.

[snip]

Sounds like the if_recur template metaprogram found here:

http://svn.boost.org/svn/boost/sandbox/variadic_templates/boost/mpl/if_recur.hpp

does what your asking, except for templates, not values.
I'd guess it could serve as a guide on how to do it for values.

-regards,

Larry