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PHP 5 Power Programming by Derick Rethans, Stig Sæther Bakken, Andi Gutmans

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3.13. Interfaces

Class inheritance enables you to describe a parent-child relationship between classes. For example, you might have a base class Shape from which both Square and Circle derive. However, you might often want to add additional “interfaces” to classes, basically meaning additional contracts to which the class must adhere. This is achieved in C++ by using multiple inheritance and deriving from two classes. PHP chose interfaces as an alternative to multiple inheritance, which allows you to specify additional contracts a class must follow. An interface is declared similar to a class but only includes function prototypes (without implementation) and constants. Any class that “implements” this interface automatically has the interface's ...

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