foreach_reverse and lockstep.

[Jonathan M Davis via Digitalmars-d]

On Thursday, March 31, 2016 03:12:34 Sean Campbell via Digitalmars-d wrote:
> Why doesn't reverse iteration of lockstep work? It does for zip.
> Is this intended or is it a bug?

Glancing over the code quickly, it looks like lockstep doesn't actually
generate a range but an object that defines opApply so that it can be used
in a foreach loop but not in general range-based algorithms. IIRC, it used
to be that opApply worked with foreach_reverse but did exactly the same
thing as foreach, so it was made an error to use it with foreach_reverse
rather than having the buggy behavior persist and confuse folks (you'd need
some sort of opApplyReverse function to go with foreach_reverse, and no such
thing exists). zip, on the other hand, generates an actual range, and if the
ranges that it's given are bidirectional ranges, then it too will be a
bidirectional range, and it'll work with foreach_reverse via the back and
popBack functions.

- Jonathan M Davis