instance_eval -- instance_exec -- class var

test.rb

# encoding: utf-8

class Person

  code = proc { puts self }

  code2 = proc { |greet| puts "#{greet} #{self}" }

  define_method :name do
    self.class.instance_eval &code
  end

  define_method :name2 do
    self.class.instance_exec "Hello", &code2
  end

  @@code = proc { puts self }

  def n
    self.class.instance_eval &@@code
  end
end

class Developer < Person;end

Person.new.n        # Person
Developer.new.n     # Developer

Person.new.name     # Person
Developer.new.name  # Developer

Person.new.name2    # Hello Person
Developer.new.name2 # Hello Developer