「More C++ Idioms/インタフェースクラス(Interface Class)」の版間の差分

* To separate an interface of a class from its implementation.

* Invoke implementation of an abstraction/class using runtime polymorphism.

 

Separating an interface of a class from its implementation is fundamental to good quality object oriented software design/programming. For object oriented programming, the principle mechanism of separation is the Interface Class. However C++ (when compared to, say, Java) provides no exclusive mechanism for expressing such a separation. In Java, '''interface''' keyword is used to specify only the public methods that are supported by an abstraction. C++ does not have such a keyword but its functionality can be expressed closely using the Interface Class idiom. The idea is to express only the public methods of an abstraction and provide no implementation of any of them. Also, lack of implementation means no instances of the interface class should be allowed.

 

An interface class contains only a virtual destructor and pure virtual functions, thus providing a construct similar to the interface constructs of other languages (e.g. Java). An interface class is a class that specifies the polymorphic interface i.e. pure virtual function declarations into a base class. The programmer using a class hierarchy can then do so via a base class that communicates only the interface of classes in the hierarchy.

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* Dependency Inversion Principle (DIP) states that implementation classes should not depend on each other. Instead, they should depend on common abstraction represented using an interface class. DIP reduces coupling in a object-oriented system.

 

Nearly all good object-oriented software in C++!

 

* [[More C++ Idioms/Capability Query|Capability Query]]

* [[More C++ Idioms/Inner Class|Inner Class]]

 

[http://www.twonine.co.uk/articles/CPPInterfaceClassesIntro.pdf C++ Interface Classes - An Introduction]

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