Question

It looks like const_missing is an instance method of Object. If so, why doesn’t this code work?

module Extensions
  def const_missing(c)
    puts c
  end
end

class Object
  include Extensions
end

NonExistent.new

In order to get it to function correctly, I have to change def const_missing to def Object.const_missing. Why?

Answer 1

This is just a consequence of the way method calls are resolved in Ruby.

First, singleton methods are checked. Then instance methods of the class, followed by the ancestors (which will be the included modules, then superclasses with their included modules).

So you could define Object.const_missing directly, or include your Module in the singleton class of Object:

class << Object
  include Extensions
end

NonExistent # => prints "NonExistent"

You could also monkeypatch Module#const_missing.