Access super variables using class object

Question

Heey I am new to Ruby. I need to create a factory method, which will return me an object of a class. Using that object I should be able to access the variables of the class. I have written the following code, but I surely have miss something.

class Super
  @@super_temp = 1

  def Super.get_instance(world)          
    platform = world
    if @@instance == nil
      if platform==1
        @@instance = BaseA.new
      else
        @@instance = BaseB.new
      end
    end
    return @@instance
  end
end

class BaseA < Super    
  @@base_temp = 2      
end


class BaseB < Super
  @@base_temp = 3    
end


class Demo
  def Demo.call_demo
    obj = Super.get_instance(0)

    puts "---------temp is #{obj.base_temp}"      
  end
end

Demo.call_demo

I need to retrieve the value of base_temp in class Demo.

Answer 1

Don't use @@ (Why should we avoid using class variables @@ in rails?) - @ solves your problem just as easily.

Aside from that, all that is missing in your code is a getter:

class Super
  @super_temp = 1

  def Super.get_instance(world)          
    platform = world
    if @instance == nil
      if platform==1
        @instance = BaseA.new
      else
        @instance = BaseB.new
      end
    end
    return @instance
  end

  def base_temp
    self.class.base_temp
  end

  def self.base_temp
    @base_temp
  end
end

class BaseA < Super    
  @base_temp = 2      
end


class BaseB < Super
  @base_temp = 3    
end


class Demo
  def Demo.call_demo
    obj = Super.get_instance(0)

    puts "---------temp is #{obj.base_temp}"      
  end
end

Demo.call_demo
# ---------temp is 3

The instance getter (implemented as self.class.base_temp) calls the class method base_temp of the instance's class. If we add prints of the internal products of the function, you can have some insights about its internals:

class Super
  def base_temp
    p self
    p self.class
    p self.class.base_temp
  end
end

BaseA.new.base_temp
# #<BaseA:0x000000027df9e0>
# BaseA
# 2

BaseB.new.base_temp
# #<BaseB:0x000000027e38b0>
# BaseB
# 3