learn-co-students/ruby-puppy-nyc-web-111918

Ruby Remembrance Lab

Learning Goals

• Use a class variable to keep track of every instance of a class that is created.
• Write a class method to access the list of all instances of a class, stored in a class variable.

Introduction

The government has decided to start tracking every new puppy that is born, just like we track every new child who is born with a birth certificate. Because you're such a notoriously skilled programmer, you've been hired by the newly minted United States Department of Canines to write a program that will do just that.

You need to write a program that stores each new puppy that is born. You will write a Dog class that initializes with a name and also stores each new instance of Dog that is instantiated.

Instructions

Code your solution in lib/dog.rb, using the test error messages from running learn as a guide to your solution.

• Create a class variable @@all set to an empty array inside your class. This array is the storage container for each instance of a Dog that gets created. In other words, every puppy that is born should get pushed into this array at the moment of instantiation––in the #initialize method! Use the self keyword inside the #initialize method to refer to the new dog you are trying to store in your @@all array.

• Write a class method, .all, that reads this variable. From inside the Dog class, we can access the @@all class variable, but whenever we might be interacting with our Dog class from the outside, this .all class method acts as our direct interface to the @@all variable.

• You will need to write a class method, .print_all, that iterates over all of the individual dogs stored in the @@all array and puts out their name to the terminal.

• Now that we've gotten these methods written out, it is time do a bit of refactoring. Rather than pushing self into the @@all variable inside of #initialize, we're extract this action into its own method. Call this method #save. The method should handle the task of pushing self into @@all. Once written, update your code in #initialize so that it uses #save.

There is one method that we'll talk about together:

The .clear_all Method

What happens if we want to clear out our list of existing dogs? It is not at all uncommon to want to "reset" or "restart" our program. You'll be building a class method, .clear_all, that does just that. This method should operate on the @@all array of existing dogs and empty that array. Hint: look up the Array#clear method.

A Note on Testing

In the test suite, you'll see this code:

expect(Dog.class_variable_get(:@@all)).to match([])

Here, we are using the .class_variable_get(name_of_class_variable) method on the Dog class. This method introspects on the class on which it is called and retrieves the value of the class variable passed into the method as an argument. We use it here in the test suite to check that you do in fact set a class variable, @@all, equal to an empty array and that you fill that array up with new dogs as they are instantiated.