Previous discussion on this: https://bugs.php.net/bug.php?id=48358

I agree that doubly linked lists need this ability to add elements in their inner content. The implementation seems OK (+- whitespaces). I however have some concern that with that patch, they interface of DLL becomes (even more) odd:

To modify the content, you have: offsetSet, offsetUnset, and insertAfterOffset, insertBeforeOffset

What are you suggesting: that they should be offsetInsertBefore() and offsetInsertAfter()?

Well, I'm not sure, since offset* comes from ArrayAccess.

But I would rather have some general-purpose discussion about interfaces of collections rather than adding one method at a time that we will not be able to rename in the future.

I honestly fear that we are not reaching a conclusion on how to name the interfaces (and particularly as we cannot rename existing methods). Nevertheless I do think a linkedlist must have these methods similar methods to add elements to after an arbitrary poisiton.

After an discussion with @colder, I think the best way to go is dropping insertAfter and adding a

add(int $index, mixed $newval)

similar to Javas API. It behaves like insertBefore. The insertAfter can be easily written as a userland function using the add method. This way we keep things simple and our interface is similar to the Java LinkedList and C# LinkedList

EDIT: NInja edit. Java add behaves like insertBefore not insertAfter..

I think the best way to go is dropping insertAfter and adding a

add(int $index, mixed $newval)

👍 since insertAfterOffset($offset, $newval) might as well be add($offset+1, $newval). I don't see a compelling reason to have this split over two methods.

The only argument I can think of for having both before and after versions is for after with an index of the last entry, effectively pushing a new value; but as push() is already available, this functionality is already available anyway.
With some minor mods, add($offset+1, $newval) can still do this when $offset is the last entry in the list; so I'll make those changes and rewrite the tests

Changes duly made as suggested to provide a single add() method

This suggestion might be a bit iffy, but I'd quite like a NULL offset to act the same as specifying count(…). It would be consistent with offsetSet() and would save having to call count()—though why you would use add() for this rather than offsetSet() or push(), I don't know. Just a thought.

I think if you want to push to the linked list, you would use push. It makes much more sense and is more readable than add(null, $value)

I dont think we should handle NULL special. Anyway the patch looks good to me and if there are no objections I will merge it before beta1.

Sounds good to me. 🐹

I squashed the branch to one commit and removed the newline changes and pushed it as 4257469. Thanks for the pull request.