7: Polymorphism

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Polymorphism
is the third essential feature of an object-oriented programming language,
after data abstraction and inheritance.

It
provides another dimension of separation of interface from implementation, to
decouple
what
from
how.
Polymorphism allows improved code organization and readability as well as the
creation of
extensible
programs that can be “grown” not only during the original creation
of the project but also when new features are desired.

Encapsulation
creates new data types by combining characteristics and behaviors.
Implementation hiding separates the interface from the implementation by making
the details
private.
This sort of mechanical organization makes ready sense to someone with a
procedural programming background. But polymorphism deals with
decoupling
in terms of
types.
In the last chapter, you saw how
inheritance
allows the treatment of an object as its own type
or
its base type. This ability is critical because it allows many types (derived
from the same base type) to be treated as if they were one type, and a single
piece of code to work on all those different types equally. The
polymorphic
method call allows one type to express its distinction from another, similar
type, as long as they’re both derived from the same base type. This
distinction is expressed through differences in behavior of the methods you can
call through the base class.

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