What is polymorphism, what is it for, and how is it used?

Question

What is polymorphism, what is it for, and how is it used?

Answer 1

Polymorphism allows the same routine (function, method) to act on different types.

Since many existing answers are conflating subtyping with polymorphism, here are three ways (including subtyping) to implement polymorphism.

• Parameteric (generic) polymorphism allows a routine to accept one or more type parameters, in addition to normal parameters, and runs itself on those types.
• Subtype polymorphism allows a routine to act on any subtype of its parameters.
• Ad hoc polymorphism generally uses routine overloading to grant polymorphic behavior, but can refer to other polymorphism implementations too.

See also:

http://wiki.c2.com/?CategoryPolymorphism

https://en.wikipedia.org/wiki/Polymorphism_(computer_science)