ruby nested classes and modules

Question

Hi,

I am familiar with the concept of nesting classes and modules within another module and grouping them in a namespace. What is the idea / purpose behind

1. Nesting classes within another class

class A
  class B
    def method_B
      ...
    end
  end
end

2.Nesting modules within another class

class A
     module c
       def method_c
         ...
       end
     end
   end

thanks, ash

Answer 1

It is all about grouping related concerns while exposing sensible semantics. As an example of number 1 an HTTP::Request (Request class embedded in a larger HTTP protocol class) is a quite different thing from an FTP::Request. With modules it enables the common ruby idiom of Behavior::InstanceMethods and Behavior::ClassMethods for handling mixins.

Answer 2

Classes are also namespaces, so it's the same idea. Class is a subclass of Module, so if you get it in the context of modules, you also get it in the context of classes.