Multiple inheritance

One feature that PHP lacks is multiple inheritance. That means a class can only extend one parent and not several classes. This presents the developers with a limitation on how they design their classes. To address this limitation, there is a known pattern called a mixin. A mixin is like a partial class that can be 'mixed in' to another class in order to supply extended functionality. Since these classes provide extra functionality, they can be reused.

To aid users with mixins, Symfony has a sfMixer class. The class that requires the mixin must extend a parent, and then declare and register the extensions using the sfMixer class.

Note

Symfony only provides a class for mixin, most of the complex sites don't really require use of mixins.