我可以从模块内部添加到类定义吗？

Question

I have a method I want to add to a class in a Rails app. I tried to separate it out into a module, like so:

module Hah
  class String
    def hurp
      "hurp durp"
    end
  end
end
#make sure the file containing the module is loaded correctly.
puts "Yup, we loaded"

#separate file
include Hah
"foobar".hurp
#should be "hurp durp"

I know the file containing the module is being loaded correctly because the puts prints correctly when I include the file, but I get an error:

undefined method `hurp' for "foobar":String

So how can I do this?

Answer 1

module Hah
  class String
    #...
  end
end

is roughly equivalent to:

class Hah::String
  #...
end

which makes a class Hah::String and does not refer to the class String in the global namespace. Note that the latter only works if module Hah was already declared (with the module keyword, Module.new , etc), while the former declares or re-opens module Hah and then within that scope declares or re-opens class String which, in context, is implicitly class Hah::String .

To open the class String in the global namespace, use:

module Hah
  class ::String
    #...
  end
end

because ::String references the class String strictly in the top level / global namespace.