This workshop is about using polymorphism to build simpler code.

1. Describe polymorphism as "being able to use different things in the same way".

2. Explain how polymorphism can be used to build simpler code.

3. Refactor some code to use polymorphism to make it simpler.

Here's some code that moves planes and cars:

def move_200(thing)
  if thing.is_a?(Car)
    thing.drive(200)
  elsif thing.is_a?(Plane)
    thing.fly(200)
  end
end

This code isn't polymorphic. It treats different things differently.

How would you add a Skateboard class?

You might do this:

def move_200(thing)
  if thing.is_a?(Car)
    thing.drive(200)
  elsif thing.is_a?(Plane)
    thing.fly(200)
  elsif thing.is_a?(Skateboard)
    thing.skate(200)
  end
end

But imagine if you refactored the Car, Plane and Skateboard to all have a move method. You could rewrite move_200 as:

def move_200(vehicle)
  vehicle.move(200)
end

The Car, Plane and Skateboard are now treated polymorphically as just "vehicles".

How does the code above relate to duck typing?

How is the polymorphic code simpler?

There's a project inside this directory. It's a very simple test assertion library. It lets you create a list of assertions and then check them. For example:

assertion_list = AssertionList.new
assertion_list.add(TruthyAssertion.new(""))
assertion_list.add(EqualAssertion.new(1, 1))

assertion_list.run_all_assertions

You job is to simplify the code by making it polymorphic.

There are two feature tests to help you refactor the code. To make the refactoring easier, there are no unit tests. Depending on the changes you make, you may be able to leave the feature tests unchanged, or you may need to change them slightly.

cd to/this/directory
bundle install

rspec

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