Ruby: Accessing class instance variables from one class in another class's class method

Question

I am working on a ruby program and have run into the following problem.

I have two classes AClass and BClass as follows:

class AClass
  attr_accessor :avar
  def initialize(input)
    @avar = input
  end
end

class BClass
  def BClass.build(aclass)
    bvalue = aclass.avar
    ....
  end
end

When i run:

aclass = AClass.new           
puts aclass.avar              
bclass = BClass.build(aclass) 

The first two lines work fine. aclass is intialized and avar is put out to the screen, but the third line creates an error. I seems that the BClass build method can not access the AClass instance variable. What do I need to do to make this work. I thought the attr_accessor would enable me to access the AClass instance variables. Thanks in advance for your input.

Answer 1

If you want to create a new type of initializer for BClass, you can do the following:

class AClass
  attr_accessor :avar

  def initialize(input)
    @avar = input
  end
end

class BClass
  attr_accessor :bvalue

  def self.build(aclass)
    bclass = self.new
    bclass.bvalue = aclass.avar
    bclass
  end
end

aclass = AClass.new 'ruby'
bclass = BClass.build aclass

This will set bclass.bvalue = aclass.avar = 'ruby'.

Answer 2

Mutu, you need to learn the basics of ruby... what you have there is not even valid ruby code.

try running this.

class AClass
  attr_accessor :avar

  def initialize(input)
    @avar = input
  end
end

class BClass
  attr_reader :bvalue

  def initialize(aclass)
    @bvalue = aclass.avar
  end
end

in irb

ruby-1.9.2-p136 :077 > a = AClass.new('ruby')
 => #<AClass:0x00000100997298 @avar="ruby"> 
ruby-1.9.2-p136 :078 > b = BClass.new(a)
 => #<BClass:0x000001009921d0 @bvalue="ruby"> 
ruby-1.9.2-p136 :079 > b.bvalue
 => "ruby" 
ruby-1.9.2-p136 :080 > a.avar
 => "ruby"