The Standard PHP Library was recently completed by a couple of data structures, namely heaps and doubly linked lists. You can find more information about those on
php.net/spl.datastructures
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I've made a new skin using the same design with blue colors: Clearblue. Check it out
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New datastructures made their way into SPL recently:
as long with two childs:
Those structures implement Iterator, ArrayAccess and Countable which makes them easy to handle. There are also multiple ways to iterate through them.
More datastructures will get implemented in the future. The goal is to implement quite every basic datastructure along with algorithms related to them. SPL could then be used as an object oriented replacement for ADT.
I've been looking everywhere for this.. :). My mind can rest now.