Polymorphism

[pol-ee-mawr-fiz-uh m] /ˌpɒl iˈmɔr fɪz əm/

noun
1.
the state or condition of being .
2.
Crystallography. crystallization into two or more chemically identical but crystallographically distinct forms.
3.
Biology. the existence of an organism in several form or color varieties.
4.
Genetics. the presence of two or more distinct phenotypes in a population due to the expression of different alleles of a given gene, as human blood groups O, A, B, and AB.
/ˌpɒlɪˈmɔːfɪzəm/
noun
1.
(biology)

2.
the existence or formation of different types of crystal of the same chemical compound
n.

1839, from polymorph + -ism.

polymorphism pol·y·mor·phism (pŏl’ē-môr’fĭz’əm)
n.

pol’y·mor’phic or pol’y·mor’phous adj.
polymorphism
(pŏl’ē-môr’fĭz’əm)

theory, programming
A concept first identified by Christopher Strachey (1967) and developed by Hindley and Milner, allowing types such as list of anything. E.g. in Haskell:
length :: [a] -> Int
is a function which operates on a list of objects of any type, a (a is a type variable). This is known as parametric polymorphism. Polymorphic typing allows strong type checking as well as generic functions. ML in 1976 was the first language with polymorphic typing.
Ad-hoc polymorphism (better described as overloading) is the ability to use the same syntax for objects of different types, e.g. “+” for addition of reals and integers or “-” for unary negation or diadic subtraction. Parametric polymorphism allows the same object code for a function to handle arguments of many types but overloading only reuses syntax and requires different code to handle different types.
See also generic type variable.
In object-oriented programming, the term is used to describe a variable that may refer to objects whose class is not known at compile time and which respond at run time according to the actual class of the object to which they refer.
(2002-08-08)