Polymorphism (computer science)

In programming languages and type theory, polymorphism (from Greek πολύς, polys, "many, much" and μορφή, morphē, "form, shape") is the provision of a single interface to entities of different data types.

Description

A polymorphic type is one whose operations can also be applied to values of some other type, or types.

There are several fundamentally different kinds of polymorphism:

• Ad hoc polymorphism: when a function denotes different and potentially heterogeneous implementations depending on a limited range of individually specified types and combinations. Ad hoc polymorphism is supported in many languages using function overloading.
• Parametric polymorphism: when code is written without mention of any specific type and thus can be used transparently with any number of new types. In the object-oriented programming community, this is often known as generics or generic programming. In the functional programming community, this is often shortened to polymorphism.
• Subtyping (also called subtype polymorphism or inclusion polymorphism): when a name denotes instances of many different classes related by some common superclass. In the object-oriented programming community, this is often simply referred to as polymorphism.

The interaction between parametric polymorphism and subtyping leads to the concepts of variance and bounded quantification.

See also

• Ad hoc polymorphism
• Bounded quantification
• Covariance and contravariance (computer science)
• Data type
• Duck typing for polymorphism without (static) types
• Function overloading
• Object-oriented programming
• Parametric polymorphism
• Polymorphic code (Computer virus terminology)
• Subtyping
• System F for a lambda calculus with parametric polymorphism.
• Type class
• Type theory
• Virtual inheritance

External links

• Polymorphism (computer science) @ Wikipedia

Computer programming