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An abstract class may have member variables as well as non-abstract methods or properties. An interface cannot. A class or abstract class can only inherit from one class or abstract class. A class or abstract class may implement one or more interfaces. An interface can only extend other interfaces.
In C#, class methods, indexers, properties and events can all be overridden. Non-virtual or static methods cannot be overridden. The overridden base method must be virtual, abstract, or override. In addition to the modifiers that are used for method overriding, C# allows the hiding of an inherited property or method.
Kotlin allows multiple inheritance of Interfaces, however, in a Diamond problem scenario, the child class must override the method that causes the inheritance conflict and specify which parent class implementation should be used. eg super<ChosenParentInterface>.someMethod()
Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should favor polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) over inheritance from a base or parent class. [2]
In most quarters, class inheritance for the sole purpose of code reuse has fallen out of favor. [citation needed] The primary concern is that implementation inheritance does not provide any assurance of polymorphic substitutability—an instance of the reusing class cannot necessarily be substituted for an instance of the inherited class.
If the derived class calls an inherited function which then calls another member function, then that function will never call any derived or overridden member functions in the derived class. However, if base class member functions use CRTP for all member function calls, the overridden functions in the derived class will be selected at compile time.
The factory method design pattern solves problems such as: How can an object's subclasses redefine its subsequent and distinct implementation? The pattern involves creation of a factory method within the superclass that defers the object's creation to a subclass's factory method.
In such a use, derived classes will supply all implementations. In such a design pattern, the abstract class which serves as an interface will contain only pure virtual functions, but no data members or ordinary methods. In C++, using such purely abstract classes as interfaces works because C++ supports multiple inheritance. However, because ...