Question

Ruby 1.9

I suddenly realize I don’t understand how to define and initialize an instance variable in Ruby. It must be used only within a certain class and not accessible out of a class at all, so attr_accessor or attr_reader is not what I need.

class MyClass

  #how do I initialize it?
  @my_var = 'some value'

  def method1
    #I need to do something with @my_var
    puts @my_var
  end
  def method2
    #I need to do something with @my_var
    puts @my_var
  end
end

a = MyClass.new
a.method1 #empty 
a.method2 #empty

So I found that there is another way to do it

class MyClass

  #is this the only way to do it?
  def initialize
    @my_var = 555
  end

  def method1
    #I need to do something with @my_var
    puts @my_var
  end

  def method2
    #I need to do something with @my_var
    puts @my_var
  end
end

a = MyClass.new
a.method1 #555; it's ok
a.method2 #555; it's ok

Well, is second approach the right one?

Answer 1

each class has an initialize() method that acts similar to a constructor in other languages, instance variables should be initialized there:

class MyClass

  def initialize
     @my_var = 'some value'
  end

  # etc...
end