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Ideally all reuse can be achieved by assembling existing components, but in practice inheritance is often needed to make new ones. Therefore inheritance and object composition typically work hand-in-hand, as discussed in the book Design Patterns (1994). [3]
The defining feature of inheritance is that both interface and implementation are inherited; if only interface is inherited, this is known as interface inheritance or subtyping. Inheritance can also be done without classes, as in prototype-based programming .
Polymorphism can be distinguished by when the implementation is selected: statically (at compile time) or dynamically (at run time, typically via a virtual function). This is known respectively as static dispatch and dynamic dispatch, and the corresponding forms of polymorphism are accordingly called static polymorphism and dynamic polymorphism.
When using polymorphism, one sometimes needs to create copies of objects by the base class pointer. A commonly used idiom for this is adding a virtual clone function that is defined in every derived class. The CRTP can be used to avoid having to duplicate that function or other similar functions in every derived class.
The relationship can be expressed explicitly via inheritance in languages that support inheritance as a subtyping mechanism. For example, the following C++ code establishes an explicit inheritance relationship between classes B and A , where B is both a subclass and a subtype of A and can be used as an A wherever a B is specified (via a ...
The concept of the virtual function solves the following problem: In object-oriented programming, when a derived class inherits from a base class, an object of the derived class may be referred to via a pointer or reference of the base class type instead of the derived class type.
What you're describing is called inheritance, and polymorphism is a consequence of inheritance. All systems using inheritance are polymorphic, but not all polymorphic systems use inheritance (in Smalltalk you can use inheritance, but it's not necessary), or even have the concept of "class" (like Self or Javascript which are based on prototypes ...
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.