Question

I am newish to Ruby and I am trying to write a method to dynamically add methods to n existing ruby class, here is what I have so far:

class Person
end

def attr_addr (target, attr)
    target.send :attr_accessor, attr
end

bob = Person.new

attr_addr(Person,"name")

bob.name = "bob"

But I get:

private method `name=' for ....

What am I doing wrong here? – am I using the wrong approach entirely ;-)?

Answer 1

Your original code works for me. Anyway, here’s another way to write it:

def attr_addr(target, attr)
  target.instance_eval "attr_accessor :#{attr}"
end

Here it is in action in an IRB session:

>> bob = Person.new
=> #<Person:0x00000000df8798>
>> bob.name = "bob"
NoMethodError: undefined method `name=' for #<Person:0x00000000df8798>
        from (irb):6
        from /home/michi/.rbenv/versions/1.9.3-p0/bin/irb:12:in `<main>'
>> attr_addr(Person, "name")
=> nil
>> bob.name = "bob"
=> "bob"
>> bob
=> #<Person:0x00000000df8798 @name="bob">