Ruby类（超级）

Question

I just started classes this week at Bloc. I've been practicing with Ruby for about 3 months but I'm finally stuck. Hoping to maybe get some help on this.

The section I'm stuck on pertains to Super

Here are the plain formatted specifications:

• The President class should accept name and age on initialization, and define getters and setters for those two attributes.

• FrancePresident and UnitedStatesPresident should inherit from President .

• The two child classes of President should define a citizenship class method, which returns "La France" or "The United States of America" , as appropriate.

• All instances of President should also have citizenship methods, which return the classes' citizenships.

• All instances of FrancePresident should append a ", bien sur" to their responses when asked for their name , age , or citizenship . This is a good case for super

Here are the RSpec Specs I'm trying to meet:

describe President do
  describe "initialization" do
    it "takes a name and age, and delegates citizenship to the class default" do
      prez = President.new("George Washington", 283)
      expect( prez.name ).to eq("George Washington")
      expect( prez.age ).to eq(283)
    end
  end

  describe "children" do
    it "is the parent of FrancePresident and UnitedStatesPresident" do
      expect( FrancePresident.superclass ).to eq(President)
      expect( UnitedStatesPresident.superclass ).to eq(President)
    end
  end
end

describe FrancePresident do
  describe "catchphrase" do
    it "sounds just right" do
      expect( FrancePresident.citizenship ).to eq("La France")
      sarcozy = FrancePresident.new("Nicolas Sarkozy", 59)
      expect( sarcozy.citizenship ).to eq("La France, bien sur")
      expect( sarcozy.age ).to eq("59, bien sur")
      expect( sarcozy.name ).to eq("Nicolas Sarkozy, bien sur")
    end
  end
end

And here is my code currently:

class President
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age 
  end
end

class FrancePresident < President
  def self.citizenship
    "La France"
  end
end

class UnitedStatesPresident < President
  def self.citizenship
    "The United States of America"
  end
end

All in all, I'm stuck with trying to get the citizenship class method to work. And from the instructions it almost seems like they want me to define a citizenship class method within the President . But I don't see how that could work and meet the specs because you can't set the citizenship individually for each child as far as I can see.

So Basically I'm stuck on the third & fourth objectives. Please get back to me on this if you've got the time.

Answer 1

In your specs you expect two flavors of citizenship responses. One with catchphrase, one without. So you must have two different methods. One class method, one instance method. It should go along these lines:

class FrancePresident < President
  def self.citizenship
    "La France"
  end

  # instance method which adds the catchphrase
  def citizenship
    append_catchphrase(self.class.citizenship)
  end

  # here's your super
  def age
    append_catchphrase(super)
  end

  def catchphrase
    'bien sur'
  end

  private

  def append_catchphrase(val)
    [val, catchphrase].join(', ')
  end
end

Answer 2

You're pretty close, you just need to define instance methods in the child classes in addition to their class methods

class FrancePresident < President
  def self.citizenship
    "La France"
  end

  def citizenship
    "La France, bien sur"
  end
end

class UnitedStatesPresident < President
  def self.citizenship
    "The United States of America"
  end

  def citizenship
    "The United States of America"
  end
end

Answer 3

First I think that citizenship method should be instance method, you can define in in your President class and override it in child classes. For your last objective here is an example:

class FrancePresident < President
  # citizenship method
  def name
    super + ", bien sur"
  end 
  def age
   super + ", bien sur"
  end
end

Answer 4

First you are not looking for a class method, it should be instance method. Here's the refactored code form what I understand:

class President
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def citizenship
    self.class.citizenship
  end

end

class FrancePresident < President
  END_STRING = ", bien sur"

  def self.citizenship
    "La France"
  end

  def age
    "#{@age}#{END_STRING}"
  end

  def name
    "#{@name}#{END_STRING}"
  end
  def citizenship
    "#{self.class.citizenship}#{END_STRING}"
  end
end

class UnitedStatesPresident < President
  def self.citizenship
    "The United States of America"
  end
end



aa = UnitedStatesPresident.new("Roosevelt", 35)
puts aa.citizenship
puts aa.name
puts aa.age
ff = FrancePresident.new("France", 35)
puts ff.citizenship
puts ff.name
puts ff.age