Neil Groves wrote:
As a general idiom the use of lazily adapting upon the invocation of begin/end would mix two responsibilities. If one considers the complications involved with managing functor and predicate state being delayed until the invocation of begin/end it appears to be a considerably more complex solution. I do not perceive a compensating advantage for this approach. Of course, I may well be missing the advantage and invite correction.
But the lazy adaption is necessary to resolve the lifetime problem: * To resolve the lifetime problem, each pipe operator should move a temporary container. * Since moving a container might invalidate iterators, each range adaptors should be applied to the last moved container (i.e. the moved container which is moved by the last pipe operator). * We cannot distinguish the last pipe operator from other pipe operators. So the only feasible timing for applying range adaptors is when begin/end is (directly or indirectly) called. Regards, Michel