I was porting my Evolutionary Computing homework written in Python over to D, and I've come across this bug I cannot for the life of me figure out.

https://gitlab.com/TheGag96/evo-pacman/blob/master/source/pacman/tree.d#L139

I don't think I could cut this down to a smaller reproducible scenario due to how bizarre and specific this problem is, so I apologize in advance if this is hard to follow.

Basically, imagine that I have a binary tree class where, due to how my program is set up, each node will have either children on both the left and right side or no children at all (the latter represented by a value of null for Tree's left and right member). I have a member function called "dup" -- marked const, mind you -- that just returns a deep copy of the tree and SHOULDN'T make any changes to the calling object.

I call this function a couple different places and it appears to function okay, but at the spot I linked, if I call .dup here, it will corrupt one of the tree's nodes and put something in its left member for no apparent reason. This oddly doesn't happen on every Tree calling this function. This could definitely be some stupid mistake on my part, but the fact that calling a const-marked function changes the state of the calling object makes me think something else is afoot here...

I would greatly appreciate anyone who would be willing to take a look at this. This bug is driving me absolutely nuts.

On 12/12/2016 12:15 AM, TheGag96 wrote:
> I was porting my Evolutionary Computing homework written in Python over
> to D, and I've come across this bug I cannot for the life of me figure out.
>
> https://gitlab.com/TheGag96/evo-pacman/blob/master/source/pacman/tree.d#L139

Not public, please pastebin.

> I don't think I could cut this down to a smaller reproducible scenario
> due to how bizarre and specific this problem is, so I apologize in
> advance if this is hard to follow.
>
> Basically, imagine that I have a binary tree class where, due to how my
> program is set up, each node will have either children on both the left
> and right side or no children at all (the latter represented by a value
> of null for Tree's left and right member). I have a member function
> called "dup" -- marked const, mind you -- that just returns a deep copy
> of the tree and SHOULDN'T make any changes to the calling object.
>
> I call this function a couple different places and it appears to
> function okay, but at the spot I linked, if I call .dup here, it will
> corrupt one of the tree's nodes and put something in its left member for
> no apparent reason. This oddly doesn't happen on every Tree calling this
> function. This could definitely be some stupid mistake on my part, but
> the fact that calling a const-marked function changes the state of the
> calling object makes me think something else is afoot here...
>
> I would greatly appreciate anyone who would be willing to take a look at
> this. This bug is driving me absolutely nuts.

On Sunday, 11 December 2016 at 11:17:50 UTC, rikki cattermole wrote:
> Not public, please pastebin.

https://github.com/TheGag96/evo-pacman/blob/master/source/pacman/tree.d#L135

I just put it on GitHub. No idea why the repo wasn't public even after I set it to be public...

On 12/12/2016 12:43 AM, TheGag96 wrote:
> On Sunday, 11 December 2016 at 11:17:50 UTC, rikki cattermole wrote:
>> Not public, please pastebin.
>
> https://github.com/TheGag96/evo-pacman/blob/master/source/pacman/tree.d#L135
>
>
> I just put it on GitHub. No idea why the repo wasn't public even after I
> set it to be public...

Can you please create a function that will cause this error to occur?
E.g. generate the source code from the tree.

That way we can test against it.

On 12/11/2016 12:43 PM, TheGag96 wrote:
> On Sunday, 11 December 2016 at 11:17:50 UTC, rikki cattermole wrote:
>> Not public, please pastebin.
>
> https://github.com/TheGag96/evo-pacman/blob/master/source/pacman/tree.d#L135
>
>
> I just put it on GitHub. No idea why the repo wasn't public even after I
> set it to be public...

Try putting an `assert(childCrossPoint !is otherCrossPoint);` before the assignment. If it fails, the variables refer to the same node. That would explain how otherCrossPoint.left gets set.

Also, what compiler are you using, what version of it, and on which platform?

On Sunday, 11 December 2016 at 11:58:39 UTC, ag0aep6g wrote:
>
> Try putting an `assert(childCrossPoint !is otherCrossPoint);` before the assignment. If it fails, the variables refer to the same node. That would explain how otherCrossPoint.left gets set.

Furthermore, I think he is calling breed on a Tree with itself.
i.e. assert(other !is this) would be a more reliable test since it won't be subject to randomness.

On Sunday, 11 December 2016 at 11:58:39 UTC, ag0aep6g wrote:
> Try putting an `assert(childCrossPoint !is otherCrossPoint);` before the assignment. If it fails, the variables refer to the same node. That would explain how otherCrossPoint.left gets set.

Ahh... This led me to it. I was about to say "That wouldn't be possible, childCrossPoint is part of a clone of the original caller!" But then I realized I did "this.getNodeList" towards the beginning instead of "child.getNodeList". I feel very silly right now, haha. Thanks for the help and your patience, guys.