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Polymorphism allows us to have a single interface to handle entities of different types. In other words, we can send the same exact message to different objects and get different results in return.
In this exercise, you'll see that there's a method in the PhonePlan class that calculates the cost of a plan differently depending on its type. However, the class should only know how to retrieve the cost, not the details of how to calculate it. Let's extract some new classes to separate the concerns and hide those details.
To start, you'll want to clone and run the setup script for the repo
git clone [email protected]:thoughtbot-upcase-exercises/replace-conditional-with-polymorphism.git
cd replace-conditional-with-polymorphism
bin/setup
Open up lib/phone_plan.rb. There you will see a single method named cost. Its corresponding tests are in spec/lib/phone_plan_spec.rb.
Replace the conditionals in cost with polymorphism. Each conditional should be represented by a new class, accompanied by their own tests.
When you're done, make sure that all the tests are passing by running:
rake
Check out the featured solution branch to see the approach we recommend for this exercise.
If you find yourself stuck, be sure to check out the associated Upcase Forum discussion for this exercise to see what other folks have said.
When you've finished the exercise, head on back to the Refactoring course to find the next exercise, or explore any of the other great content on Upcase.
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