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polymorphism    音标拼音: [p,ɑlim'ɔrfɪzəm] [p,ɑlim'ɔrfɪzm]
n. 多形,同质异像,多形现象

多形,同质异像,多形现象

polymorphism
多型

polymorphism
n 1: (genetics) the genetic variation within a population that
natural selection can operate on
2: (chemistry) the existence of different kinds of crystal of
the same chemical compound [synonym: {polymorphism},
{pleomorphism}]
3: (biology) the existence of two or more forms of individuals
within the same animal species (independent of sex
differences)

Polymorphism \Pol`y*mor"phism\, n.
1. (Crystallog.) Same as {Pleomorphism}.
[1913 Webster]

2. (Biol.)
(a) The capability of assuming different forms; the
capability of widely varying in form.
(b) Existence in many forms; the coexistence, in the same
locality, of two or more distinct forms independent of
sex, not connected by intermediate gradations, but
produced from common parents.
[1913 Webster]

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)


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