How do I set an attr_accessor for a dynamic instance variable?

Question

I dynamically created an instance variable within my class:

class Mine   attr_accessor :some_var    def intialize     @some_var = true   end    def my_number num     self.instance_variable_set "@my_#{num}", num   end end 

How do I make @my_#{num} now as an attr value?

e.g. I want to be able to do this:

dude = Mine.new dude.my_number 1 dude.my_1 => 1 

Answer 1

this answer doesn't pollutes the class space, example.. if i do mine.my_number 4 then the other instances of Mine will not get the my_4 method.. this happens because we use the singleton class of the object instead of the class.

class Mine   def my_number num     singleton_class.class_eval { attr_accessor "my_#{num}" }     send("my_#{num}=", num)   end end  a = Mine.new b = Mine.new a.my_number 10 #=> 10 a.my_10 #=> 10 b.my_10 #=> NoMethodError 

Answer 2

This can be accomplished using __send__. Here:

class Mine   attr_accessor :some_var    def intialize     @some_var = true   end    def my_number num     self.class.__send__(:attr_accessor, "my_#{num}")     self.__send__("my_#{num}=", num)   end end  dude = Mine.new dude.my_number 1 puts dude.my_1  => 1