Ruby how to modify a instance variable from another method?

Question

Basically, i need to increase by one my variable variable_position every time the method set_variable_value is called, so every bin_val variable created through that method gets created with a different incremental variable_position parameter starting from 16.

Right know, it goes from 15 (see initialize method) to 16 in the first method call, but then i stays at 16 no matter how many times the method is called.

require "./my_math.rb"
    class Rules
      attr_accessor :variable_position
      JUMP_ARR = [";JGT", ";JEQ", ";JGE", ";JLT", ";JNE", ";JLE", ";JMP"]

      def initialize
        @variable_position = 15
      end

      # A instructions have to be 16 bit long
      def self.a_16_bit (line)
        a_rules = Rules.new
        if line[1] == 'R'
          bin_val = a_rules.set_reserved_variable_value(line)
        elsif (/^[[:alpha:]]+$/).match(line[1..line.length])
          bin_val = a_rules.set_variable_value #HERE IS WHERE I CALL THE METHOD
        else
          bin_val = MyMath.to_binary(line[1..line.length])
        end
        n = bin_val.to_s.length
        m = 16 - n
        complete_number = ("0"*m) + bin_val.to_s
      end

      def set_variable_value
        @variable_position += 1 #HERE IS WHERE I TRY TO INCREASE THE VALUE
        bin_val = MyMath.to_binary(@variable_position)
      end
    end

Thanks a lot for reading.

@mudasobwa is right in the self.a_16_bit method; I added a comment so you can find it easier — Sebastian Delgado
– Sebastian Delgado, Commented Mar 26, 2017 at 7:25
@SebastianDelgado after calling ::a_16_bit a new Rules object is created. So every time you call that method, you are initializing a new object, with a new instance variable. Plus you call it only once from within ::a_16_bit, so it can change only by 1. Maybe @variable_position should be a class instance variable? — Adam Zapaśnik
– Adam Zapaśnik, Commented Mar 26, 2017 at 7:52

JPCL · Accepted Answer · 2017-03-26 08:21:11Z

3

When you call a_rules = Rules.new you are creating a new instance of Rules. So the constructor initialize is setting the @variable_position value to 15 once for every instance.

Then, when you call the method bin_val = a_rules.set_variable_value it increases the value of @variable_position once because you are still working on the same instance.

I suggest that @variable_position should be a class variable. That way you won't be resetting it's value every time you instance a new object.

answered Mar 26, 2017 at 8:21

JPCL

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Sebastian Delgado Over a year ago

Thanks for your help

Aleksei Matiushkin · Accepted Answer · 2017-03-26 08:26:43Z

1

You don’t need an instance of the object at all:

require "./my_math.rb"
class Rules
  JUMP_ARR = [";JGT", ";JEQ", ";JGE", ";JLT", ";JNE", ";JLE", ";JMP"]

  @variable_position = 15

  # A instructions have to be 16 bit long
  def self.a_16_bit (line)
    bin_val = if line[1] == 'R'
                # code from set_reserved_variable_value(line) here
              elsif (/^[[:alpha:]]+$/).match(line[1..line.length])
                MyMath.to_binary(@variable_position += 1)
              else
                MyMath.to_binary(line[1..line.length])
              end
    n = bin_val.to_s.length
    m = 16 - n
    complete_number = ("0"*m) + bin_val.to_s
  end
end

In your current code you are messing with instance variables and class methods.

answered Mar 26, 2017 at 8:26

Aleksei Matiushkin

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1 Comment

Sebastian Delgado Over a year ago

Thanks for your help

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