In a new post to his blog Benjamin Eberlei talks about enum data types in PHP and how the is getting close but still isn't quite there yet.

If you want to implement Enum behaviour with a simple string or int value you end up with having to validate the values at several different locations in the code rather than being able to strictly enforce the Enum structure by using typehints.

In an effort to try to help the situation he and a colleague came up with an abstract class MyEnum that uses the __toString method to do value checking. Code examples are included for the class and how to use it.