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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.
Some languages like Go do not support inheritance at all. Go states that it is object-oriented, [37] and Bjarne Stroustrup, author of C++, has stated that it is possible to do OOP without inheritance. [38] The doctrine of composition over inheritance advocates implementing has-a relationships using composition instead of inheritance. For ...
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]
Since all polymorphism has a genetic basis, genetic polymorphism has a particular meaning: Genetic polymorphism is the simultaneous occurrence in the same locality of two or more discontinuous forms in such proportions that the rarest of them cannot be maintained just by recurrent mutation or immigration, originally defined by Ford (1940).
[citation needed] In C++ private inheritance can be used as a form of implementation inheritance without substitutability. Whereas public inheritance represents an "is-a" relationship and delegation represents a "has-a" relationship, private (and protected) inheritance can be thought of as an "is implemented in terms of" relationship. [16]
[citation needed] Examples of strictly object-based languages – supporting an object feature but not inheritance or subtyping – are early versions of Ada, [2] Visual Basic 6 (VB6), and Fortran 90. Some classify prototype-based programming as object-based even though it supports inheritance and subtyping albeit not via a class concept.
One issue with static polymorphism is that without using a general base class like AbstractShape from the above example, derived classes cannot be stored homogeneously – that is, putting different types derived from the same base class in the same container.
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 .