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- [Voiceover] Hi, welcome
to the second video

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of this section, polymorphism.

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In the previous video, we
learned about inheritance.

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In this video, we'll go through
the concept of polymorphism,

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and take a look at an example.

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Polymorphism allows us to write code

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that is less dependent on the types

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we are trying to manipulate.

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This can make our code
clearer and more efficient.

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It means different forms.

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If the objects that we code

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can be more than one type of thing,

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that we can take advantage of this.

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Boiled down to its simplest definition,

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polymorphism is this:

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Any sub-class can be used

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as part of the code that
uses the super-class.

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This means we can write code

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that is simpler and easier to understand,

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and also easier to modify or change.

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Also, we can write code
for the super-class,

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and rely on the fact that
no matter how many times

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it is sub-classed, within
certain parameters,

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the code will still work.

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Let's discuss an example.

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Suppose we want to use polymorphism

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to help write a zoo management game,

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where we have to feed and
tend to the needs of animals.

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We will probably want to have
a function such as "feed."

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We will also probably
want to pass an instance

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of the animal to be fed
into the feed function.

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A zoo of course has many types of animals.

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Lion, elephant and three-toed sloth.

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With our new knowledge of C++ inheritance,

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it will make sense to code an animal class

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and have all the different
types of animal inherit from it.

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If we want to write a function, "feed,"

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that we can pass lion,
elephant, and three-toed sloth

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into as a parameter,

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it might seem like we need
to write a feed function

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for each and every type of animal.

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However, we can write
polymorphic functions,

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with polymorphic return
types and arguments.

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Take a look at this definition

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of the hypothetical feed function:

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This function has the animal
reference as a parameter.

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Meaning that, any object
that is built from a class

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that extends animal can be passed into it.

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So you can even write code today,

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and make another sub-class
in a week, month, or year.

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And the very same functions
and data structures

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will still work.

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Also, we can enforce upon our sub-classes,

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a set of rules for what
they can and cannot do,

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as well as how they do it.

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So, good design in one stage

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can influence it at other stages.

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But will we really ever want to

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instantiate an actual animal?

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We'll find out.

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In this video, we've
looked at polymorphism.

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Great.

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Next, as I just said,
we'll see abstract classes,

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virtual and pure virtual functions.