Parametric polymorphism

In programming languages and type theory, parametric polymorphism allows a single piece of code to be given a "generic" type, using variables in place of actual types, and then instantiated with particular types as needed.^: 340 Parametrically polymorphic functions and data types are sometimes called generic functions and generic datatypes, respectively, and they form the basis of generic programming.

Parametric polymorphism may be contrasted with ad hoc polymorphism. Parametrically polymorphic definitions are uniform: they behave identically regardless of the type they are instantiated at.^{: 340 : 37} In contrast, ad hoc polymorphic definitions are given a distinct definition for each type. Thus, ad hoc polymorphism can generally only support a limited number of such distinct types, since a separate implementation has to be provided for each type.