Question

Newbie here, having a hard time understanding Class methods and why I cannot get an attribute to show up correctly in the instance.

class Animal
  attr_accessor :noise, :color, :legs, :arms

  def self.create_with_attributes(noise, color)
    animal = self.new(noise)
    @noise = noise
    @color = color
    return animal
  end

  def initialize(noise, legs=4, arms=0)
    @noise = noise
    @legs = legs
    @arms = arms
    puts "----A new animal has been instantiated.----"
  end
end

animal1 = Animal.new("Moo!", 4, 0)
puts animal1.noise
animal1.color = "black"
puts animal1.color
puts animal1.legs
puts animal1.arms
puts

animal2 = Animal.create_with_attributes("Quack", "white")
puts animal2.noise
puts animal2.color

When I use the class method create_with_attributes (on animal.2), I expect "white" to appear when I puts animal2.color.

It seems as though I have defined it using attr_accessor just like I have “noise”, and yet noise appears correctly while color will not. I do not get an error when I run this program, but the .color attribute is just not appearing. I believe it is because I have somehow labeled it incorrectly in the code.

Answer 1

self.create_with_attributes is a class method, so setting @noise and @color within it is not setting an instance variable, but instead what’s known as a class instance variable.

What you want to do is set the variables on the instance you’ve just created, so instead, change self.create_with_attributes to look something like:

 def self.create_with_attributes(noise, color)
     animal = self.new(noise)
     animal.noise = noise
     animal.color = color
     animal
 end

which will set the attributes on your new instance, instead of on the class itself.