Problem with class variables

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January 16th, 2012, 05:33 PM

haosmark

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Problem with class variables

I'm trying to learn Ruby by reading "Humble Little Ruby" book and yesterday I got stuck and wondering if anyone here can help me.
Basically the code creates a class "boogeyman" with several methods, right now the author is explaining class variables, so he creates one in the boogeyman class to keep track of which instance of boogeyman was created last by user. I copied the code word to word, but still get an error:

Quote:

undefined method `latest' for Boogeyman:Class (NoMethodError)

Here's the code itself:

Code:

class Boogeyman
  attr_writer :scare_factor
  
  def initialize(name, location)
    @name = name
    @location = location
    
    @@latest = @name
    @@location = @location
    puts "Yes, master?"
  end
  
  def change_location(new_location)
    @location = new_location
    puts "I moved to #{new_location}!"
    self.get_info
  end
  
  def change_name(new_name)
    @name = new_name
    puts "I shall be called #{new_name} from now on."
    self.get_info
  end
  
  def get_info
    puts "I'm #{@name} in #{@location}."
  end
  
  def scare_factor
    return "#{@scare_factor / 1000}Fg"
  end
  

  protected
  def are_you_a_monster?(whosasking)
    puts "Yes #{whosasking}, I'm a monster!"
    return true
  end
  
  private
  def phone_home(message)
    puts message
  end
  
  public
  def scare(who)
    phone_home("I just scared the living **** out of #{who}")
  end
end

#test the class
monster1 = Boogeyman.new("Crazy Cal", "Nashville, TN")
monster2 = Boogeyman.new("Gory Gary", "Reston, WV")
puts Boogeyman.latest
#monster1.scare("bitch")
#monster1.scare_factor = 6000
#puts monster1.scare_factor
#monster1.change_location("Wyoming")
#monster1.change_name("Beezlebub")

Class variable is create in initialize method.
Thanks for the help in advance.

January 17th, 2012, 10:28 AM

Schol-R-LEA

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The problem here is that class variables are private to the class in question; thus, trying to access the variable Bogeyman.latest will cause this error, since while the variable has been created and set, it isn't visible from outside of the class.

Worse, you cannot have an attribute for the class vars either, as attributes are part of the object, not the class. There are extensions in Rails for class attributes, but in plain Ruby, you can't access the class variables from outside of the class except through a class method.

I'm not sure what the book's author had in mind when he or she wrote that; it may have been intentional, to see if you picked up on the error, in which case it will probably say so later in the text.

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Problem with class variables

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