On 8/9/2011 11:17 PM, Joel de Guzman wrote:
On 8/10/2011 12:56 PM, Eric Niebler wrote:
A sequence created by push_back is a Forward Sequence, which means you can't call pop_back on it. I think that's a serious shortcoming. Fusion needs something like MPL's Back Extensible and Front Extensible concepts.
http://www.boost.org/doc/libs/1_47_0/libs/mpl/doc/refmanual/back-extensible-...
Unfortunately, this would likely require a redesign of the whole (push|pop)_(front|back) mechanism.
Man, this is a major bummer, alright. One plausible clean way I can think of is:
1) Make single_view random_access (if it's not already; IIRC No).
I implemented this not too long ago.
2) Make joint_view assume the least sequence category of its subsumed sequences. There's already some work done related to this where joint_view inherits the 'associative'-ness of its held sequences.
I don't think that's good enough. Take my example above. In, push_back(nil(), 1), the traversal type of nil is Forward, and so too would be the resulting view. It probably makes sense to see how MPL manages it. -- Eric Niebler BoostPro Computing http://www.boostpro.com