Since PHP 7.0 release, a raising concern for developers is the performance issue of SPL classes. PHP 7.0 does not bring any improvement to early designed SPL classes, and many developers are now sceptical about using it further. Many developers have written custom libraries and extensions for PHP to improve the data structure efficiency. One of such extensions is PHP DS, a specialized extension for PHP 7 data structures. The extension is written by Joe Watkins and Rudi Theunissen. The official documentation of PHP DS extension can be found in the PHP manual at http://php.net/manual/en/book.ds.php.

The library works as an alternative to PHP array, which is a very flexible, dynamic, hybrid data structure. This extension comes up with lots of pre-built data structures such as set, map, sequence, collection, vector, stack, queue, priority queue, and so on. We will explore them in the next few sections.