This extension is EXPERIMENTAL. The behaviour of this extension—including the names of its functions and any other documentation surrounding this extension—may change without notice in a future release of PHP. This extension should be used at your own risk.
In Object Oriented Programming, it is common to see the composition of simple classes (and/or instances) into a more complex one. This is a flexible strategy for building complicated objects and object hierarchies and can function as a dynamic alternative to multiple inheritance. There are two ways to perform class (and/or object) composition depending on the relationship between the composed elements: Association and Aggregation.