Using Traits and Interfaces

It is considered a best practice to make use of interfaces as a means of establishing the classification of a set of classes, and to guarantee the existence of certain methods. Traits and Interfaces often work together, and are an important aspect of implementation. Wherever you have a frequently used Interface that defines a method where the code does not change (such as a setter or getter), it is useful to also define a Trait that contains the actual code implementation.

How to do it...

1. For this example, we will use ConnectionAwareInterface, first presented in Chapter 4, Working with PHP Object-Oriented Programming. This interface defines a setConnection() method that sets a $connection property. Two classes in the Application\Generic namespace, CountryList and CustomerList, contain redundant code, which matches the method defined in the interface.
2. Here is what CountryList looks like before the change:

   class CountryList
   {
     protected $connection;
     protected ...