Polymorphism (computer science): Difference between revisions

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{{Distinguish|Polymorphic code}}

{{Polymorphism}}

In [[programming language theory]] and [[type theory]], '''polymorphism''' is the useapproach ofthat oneallows symbola tovalue representtype to multipleassume different types.<ref name="Luca">{{Cite journal |last1=Cardelli |first1=Luca |author1-link=Luca Cardelli |last2=Wegner |first2=Peter |author2-link=Peter Wegner (computer scientist)|doi=10.1145/6041.6042 |title=On understanding types, data abstraction, and polymorphism |journal=[[ACM Computing Surveys]] |volume=17 |issue=4 |pages=471–523 |date=December 1985 |url=http://lucacardelli.name/Papers/OnUnderstanding.A4.pdf |citeseerx=10.1.1.117.695 |s2cid=2921816}}: "Polymorphic types are types whose operations are applicable to values of more than one type."</ref>

In [[object-oriented programming]], polymorphism is the provision of one [[Interface (object-oriented programming)|interface]] to entities of different [[data type]]s.<ref>{{cite web |url=http://www.stroustrup.com/glossary.html#Gpolymorphism |last1=Stroustrup |first1=Bjarne |author1-link=Bjarne Stroustrup |title=Bjarne Stroustrup's C++ Glossary |date=February 19, 2007 |quote=polymorphism – providing a single interface to entities of different types.}}</ref> The concept is borrowed from a principle in [[biology]] where an organism or species can have many different forms or stages.<ref name="Moved">{{cite web |title=Polymorphism |work=The Java Tutorials: Learning the Java Language: Interfaces and Inheritance |publisher=Oracle |url=https://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html |access-date=2021-09-08}}</ref>

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===Ad hoc polymorphism===

{{Further|Ad hoc polymorphism}}

[[Christopher Strachey]] chose the term ''ad hoc polymorphism'' to refer to polymorphic functions that can be applied to arguments of different types, but that behave differently depending on the type of the argument to which they are applied (also known as [[function overloading]] or [[operator overloading]]).<ref name=Strachey00/> The term "[[ad hoc]]" in this context is not pejorative: instead, it means that this form of polymorphism is not a fundamental feature of the type system. In the [[Java (programming language)|Java]] example below, the <code>Addadd</code> functions seem to work generically over two types ([[Integer (computer science)|integer]] and [[String (computer science)|string]]) when looking at the invocations, but are considered to be two entirely distinct functions by the [[compiler]] for all intents and purposes:

<syntaxhighlight lang="java">

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static void letsHear(final Pet pet) {

System.out.println(pet.speak());

}