Including/Extending the Kernel doesn't add those methods on main:Object

Question

I\'m trying to add a method into the Kernel module, but instead of reopening the Kernel and directly defining an instance method, I\'m writing a mo

Answer 1

You want include, not extend.

include adds the contents of the module as instance methods (like when you open a class or module normally); extend adds them as class methods (so in your example, you could call Kernel.hello, though this isn't what you want).

You might now be inclined to try this:

module Talk
  def hello
    puts "hello there"
  end
end

module Kernel
  include Talk
end

But this won't work either, because main has already been instantiated, and include simply alters the ancestry of Kernel.

You could force main to include your module at runtime, like this:

# (in global scope)
class << self
  include Talk
end

This way, you're altering the metaclass of main, not Kernel (which would imply including it on a ton of other object you may not want).

If you do, you can also just do an include Talk in global scope, but beware that this will pollute integers and other things with your methods.