• Sean Campbell (2/2) Mar 30 2016 Why doesn't reverse iteration of lockstep work? It does for zip.
• ZombineDev (11/13) Mar 31 2016 Lockstep is actually not a range. It overloads the opApply[1]
• Jack Stouffer (2/4) Mar 31 2016 Please file an enhancement request at issues.dlang.org
• Jonathan M Davis via Digitalmars-d (13/15) Apr 01 2016 Glancing over the code quickly, it looks like lockstep doesn't actually
• Simen Kjaeraas (6/8) Apr 01 2016 Actually, it exists and it works. It's just not implemented for
• ZombineDev (2/10) Apr 01 2016 I'm already working on a PR. I think I can be ready by tomorrow.
• ZombineDev (2/15) Apr 01 2016 https://issues.dlang.org/show_bug.cgi?id=15860
• Simen Kjaeraas (5/18) Apr 01 2016 Sure, but mine's ready now :p

Sean Campbell <sycam.inc gmail.com> writes:

Why doesn't reverse iteration of lockstep work? It does for zip. 
Is this intended or is it a bug?

ZombineDev <petar.p.kirov gmail.com> writes:

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

Lockstep is actually not a range. It overloads the opApply[1] 
operator to support foreach. To support foreach_reverse, it would 
also have to override opApplyReverse. I'd say that it's not a bug 
but still a valid enhancement request. BTW the upcomming release 
has better documentation on the differences between lockstep [2] 
and zip [3].

[1]: 
https://github.com/D-Programming-Language/phobos/blob/master/std/range/package.d#L4153

[2]: http://dlang.org/phobos-prerelease/std_range#lockstep

[3]: http://dlang.org/phobos-prerelease/std_range#zip

Jack Stouffer <jack jackstouffer.com> writes:

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

Please file an enhancement request at issues.dlang.org

Jonathan M Davis via Digitalmars-d <digitalmars-d puremagic.com> writes:

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

Simen Kjaeraas <simen.kjaras gmail.com> writes:

On Friday, 1 April 2016 at 14:37:36 UTC, Jonathan M Davis wrote:
 (you'd need some sort of opApplyReverse function to go with 
 foreach_reverse, and no such thing exists).

Actually, it exists and it works. It's just not implemented for
lockstep. I'm trying to clean up my Phobos repo so I can make a
PR to fix this. Apparently I need to learn more git. :)

--
   Simen

ZombineDev <petar.p.kirov gmail.com> writes:

On Friday, 1 April 2016 at 16:10:01 UTC, Simen Kjaeraas wrote:
 On Friday, 1 April 2016 at 14:37:36 UTC, Jonathan M Davis wrote:
 (you'd need some sort of opApplyReverse function to go with 
 foreach_reverse, and no such thing exists).

 Actually, it exists and it works. It's just not implemented for
 lockstep. I'm trying to clean up my Phobos repo so I can make a
 PR to fix this. Apparently I need to learn more git. :)

 --
   Simen

I'm already working on a PR. I think I can be ready by tomorrow.

ZombineDev <petar.p.kirov gmail.com> writes:

On Friday, 1 April 2016 at 17:44:40 UTC, ZombineDev wrote:
 On Friday, 1 April 2016 at 16:10:01 UTC, Simen Kjaeraas wrote:
 On Friday, 1 April 2016 at 14:37:36 UTC, Jonathan M Davis 
 wrote:
 (you'd need some sort of opApplyReverse function to go with 
 foreach_reverse, and no such thing exists).

 Actually, it exists and it works. It's just not implemented for
 lockstep. I'm trying to clean up my Phobos repo so I can make a
 PR to fix this. Apparently I need to learn more git. :)

 --
   Simen

 I'm already working on a PR. I think I can be ready by tomorrow.

https://issues.dlang.org/show_bug.cgi?id=15860

Simen Kjaeraas <simen.kjaras gmail.com> writes:

On Friday, 1 April 2016 at 17:44:40 UTC, ZombineDev wrote:
 On Friday, 1 April 2016 at 16:10:01 UTC, Simen Kjaeraas wrote:
 On Friday, 1 April 2016 at 14:37:36 UTC, Jonathan M Davis 
 wrote:
 (you'd need some sort of opApplyReverse function to go with 
 foreach_reverse, and no such thing exists).

 Actually, it exists and it works. It's just not implemented for
 lockstep. I'm trying to clean up my Phobos repo so I can make a
 PR to fix this. Apparently I need to learn more git. :)

 --
   Simen

 I'm already working on a PR. I think I can be ready by tomorrow.

Sure, but mine's ready now :p

https://github.com/D-Programming-Language/phobos/pull/4138

--
   Simen