instance_eval's behaviour inside a instance method

Question

Below is my snippet which i tried,

class Person
  def test(arg)
    self.class.instance_eval do
      define_method(arg) {puts "this is a class method"}
    end
  end
end

irb(main):005:0> Person.new.test("foo")
=> #<Proc:0x9270b60@/home/kranthi/Desktop/method_check.rb:4 (lambda)>

irb(main):003:0> Person.foo
NoMethodError: undefined method `foo' for Person:Class

irb(main):007:0> Person.new.foo
this is a class method
=> nil

Here am adding a method to the Person class dynamically using instance_eval and define_method. But why is this behaving as instance method?. Is that completely dependent on self? Confused. Can anyone explain me or a reference link also appreciated.

Answer 1

It's because define_method defines instance method of the receiver . Your receiver ( self ) is Person class, so it defines instance method of Person class. You can achieve what you want accessing to Person 's metaclass:

def test(arg)
  class << self.class
    define_method(arg) { puts 'this is a class method' }
  end
end

I haven't tested it, but it should work.