INTRO TO CLASSES - Bloc Checkpoint

Attr Accessor

Getter and setter methods are so common that Ruby provides a shortcut to create them. The attr_accessor method creates a getter and setter method based on an argument. You call the attr_accessor with a Symbol argument:

class Square
  attr_accessor :size
end

s = Square.new
s.size = 10   # This is the setter
s.size        #=> 10 # This is the getter
Notice how we have both the getter and setter methods for size, because we called:

  attr_accessor :size
What's going on here? Ruby is essentially writing the size=() and size methods for you when you add attr_accessor :size to your class.

To complete this exercise, create a class named Playlist. It should have attributes for name, author, and song_list. These attributes should readable and writable.

SPEC
describe "Playlist" do
  describe "instance variables" do
    it "should be able to create a country playlist" do
      playlist = Playlist.new
      
      # Setters
      playlist.name = "Country"
      playlist.author = "Blake Shelton"
      playlist.song_list = ["Sure Be Cool If You Did", "God Gave Me You"]

      # Getters
      expect( playlist.name ).to eq("Country")
      expect( playlist.author ).to eq("Blake Shelton")
      expect( playlist.song_list ).to eq(["Sure Be Cool If You Did", "God Gave Me You"])
    end
    it "should be able to create a Rock playlist" do
      playlist = Playlist.new
      
      # Setters
      playlist.name = "Rock"
      playlist.author = "R&R"
      playlist.song_list = ["Radioactive", "Clouds"]

      # Getters
      expect( playlist.name ).to eq("Rock")
      expect( playlist.author ).to eq("R&R")
      expect( playlist.song_list ).to eq(["Radioactive", "Clouds"])
    end
  end
end
CODE
class Playlist
  attr_accessor :name
  attr_accessor :author
  attr_accessor :song_list
end

Basics

Create a Book class with two instance methods. The set_title_and_author instance method should act as a setter for two attributes by those names -- taking title and author arguments and setting them as attributes on a book instance. There is no direct test spec for this method, its implementation will be tested indirectly in the description method (below).

Note that this "setter" method doesn't have a = in its title. The equal sign is just a convention for clarity. It is unecessary here, because the method name itself implies its purpose.

The description method should return a string with both instance variables, formatted as:

"Title was written by author"

Remember that the words "title" and "author" will be replaced by instance variables defined in the title_and_author method.

SPEC
describe "Book" do
  describe "description" do
    it "should return title and author in description" do
      book = Book.new
      book.set_title_and_author("Ender's Game","Orson Scott Card")
      expect( book.description ).to eq("Ender's Game was written by Orson Scott Card")
    end
  end
end

CODE
class Book
  def set_title_and_author (title, author)
    @title = title
    @author = author
  end
  
  def description 
    "#{@title} was written by #{@author}"
  end
end

Getters and Setters

As we learned in the checkpoint, getter and setter methods allow you to access attributes of a class instance.

Let's look at another example as a refresher. Below we define two methods in the Car class. The color=(c) method sets the @color instance variable, and the color method gets the @color instance variable. The last two lines of code below demonstrate how the getter and setter methods are used on the ferrari instance of the Car class:

class Car
  def color=(c)
    @color = c
  end

  def color
    @color
  end
end

ferrari = Car.new

ferrari.color= "Red" # setter
ferrari.color        # getter
#=> "Red"

SPEC
describe "Book" do
#   describe "instance variables" do
#     it "should be able get and set the title to 'LOTR'" do
#       b = Book.new
#       # Ability to get/set title
#       b.title = "LOTR"
#       expect( b.title ).to eq("LOTR")
#       # Ability to get/set pages
#       b.pages = 1000
#       expect( b.pages ).to eq(1000)
#       # Ability to get/set author
#       b.author = "J. R. R. Tolkien"
#       expect( b.author ).to eq("J. R. R. Tolkien")
#     end
#     it "should be able to set the title to 'Hitchhiker's Guide'" do
#       b = Book.new
#       # Ability to get/set title
#       b.title = "Hitchhiker's Guide"
#       expect( b.title ).to eq("Hitchhiker's Guide")
#       # Ability to get/set pages
#       b.pages = 700
#       expect( b.pages ).to eq(700)
#       # Ability to get/set author
#       b.author = "Douglas Adams"
#       expect( b.author ).to eq("Douglas Adams")
#     end
#   end
# end
CODE
class Book
  
  def title=(t)
    @title = t
  end
  
  def author=(a)
    @author = a
  end
  
  def pages=(p)
    @pages = p
  end
  
  def title
    @title
  end
  
  def author
    @author
  end
  
  def pages
    @pages
  end
end

RSpec Class Errors

SPEC
describe MadeUpClass do
  describe "#return_string" do
    it "returns the right string" do
      expect( MadeUpClass.new.return_string ).to eq("String to return")
    end
  end
end
CODE
class MadeUpClass
  def return_string
  p = "String to return"
   end 
end