polymorphism

pol·y·mor·phism   (pŏl'ē-môr'fĭz'əm)    n.   Biology The occurrence of different forms, stages, or types in individual organisms or in organisms of the same species, independent of sexual variations. Chemistry Crystallization of a compound in at least two distinct forms. Also called pleomorphism. pol'y·mor'phic, pol'y·mor'phous adj., pol'y·mor'phous·ly adv.

Main Entry: poly·mor·phism
Pronunciation: "päl-i-'mor-"fiz-&m
Function: noun
: the quality or state of existing in or assumingdifferent forms: as a (1) : existence of a species in several forms independent of the variations of sex (2) : existence of a gene in several allelic forms (3) : existence of a molecule (as an enzyme) in several forms in a single species b : the property of crystallizing in two or more forms with distinct structure

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

1. The occurrence of different forms, stages, or types in individual organisms or in organisms of the same species, independent of sexual variations.

2. Crystallization of a compound in at least two distinct forms. Also called pleomorphism.

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pol'y·mor'phic or pol'y·mor'phous adj.

polymorphism   (pŏl'ē-môr'fĭz'əm)  Pronunciation Key  The existence of two or more different forms in an adult organism of the same species, as of an insect. In bees, the presence of queen, worker, and drone is an example of polymorphism. Differences between the sexes and between breeds of domesticated animals are not considered examples of polymorphism. The crystallization of a compound in at least two distinct forms. Diamond and graphite, for example, are polymorphs of the element carbon. They both consist entirely of carbon but have different crystal structures and different physical properties.

polymorphism 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)