The Standard PHP Library (SPL), is one of the best possible features of the PHP language in last few years. SPL was created to solve common problems which were lacking in PHP. SPL extended the language in many ways but one of the striking features of SPL is its support of data structures. Though SPL is used for many other purposes, we are going to focus on the data structure part of SPL. SPL comes with core PHP installations and does not require any extension or change in configurations to enable it.

SPL provides a set of standard data structures through Object-Oriented Programming in PHP. The supported data structures are:

• Doubly linked lists: It is implemented in SplDoublyLinkedList.
• Stack: It is implemented in SplStack by using SplDoublyLinkedList.
• Queue: It is implemented in SplQueue by using SplDoublyLinkedList.
• Heaps: It is implemented in SplHeap. It also supports max heap in SplMaxHeap and min heap in SplMinHeap.
• Priority queue: It is implemented in SplPriorityQueue by using SplHeap.
• Arrays: It is implemented in SplFixedArray for a fixed size array.
• Map: It is implemented in SplObjectStorage.

In coming chapters, we are going to explore each of the SPL data structure implementations and know their pros and cons, along with their performance analysis with our implementation of corresponding data structures. But as these data structures are already built in, we can use them for a quick turnaround of features and applications.

After the release of PHP 7, everyone was happy with the performance boost of the PHP application in general. PHP SPL is not having the similar performance boost in many cases, but we are going to analyze those in upcoming chapters.