Question

o = Object.new

class << o
  public :puts
end
o.puts "1. #{o.class.method_defined? :puts}"              => false
o.puts "2. #{o.class.method_defined? :public_methods}     => true

method_defined? still give me false? even if I declare puts as public, why?

Answer 1

o.class
=> Object

Object.method_defined? :puts
=> false

o.singleton_class
=> #<Class:#<Object:0x2b23858>>

o.singleton_class.method_defined? :puts
=> true

I think the code above shows very clear explanation. If you modify the object itself, you should use singleton_class to access rather than class because the original class does not contain the singleton methods you added.