ruby metaprogramming usage using define_method and undef_method.txt

foo.rb

class Foo
  puts "define_method: #{defined?(define_method).inspect}"
  define_method(:bar) { puts "one" }
end

a = Foo.new
a.bar

class Foo
  class << self
    undef_method :define_method #why whis works
  end
  # undef_method :define_method # and this does not
  puts "define_method: #{defined?(define_method).inspect}"
end

class Foo
  puts "define_method: #{defined?(define_method).inspect}"
  define_method(:baz) { puts "two" }
rescue
  puts "define_method is undefined"
end

# on irb
# self.class.send(:define_method, :foo) { puts "foo" }
# irb is running as a special TopLevel object