ruby nested classes and modules

Question

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

Nesting classes within another class

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

Nesting modules within another class

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

thanks, ash

Chuck · Accepted Answer · 2010-05-14 15:51:23Z

3

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.

answered May 14, 2010 at 15:51

Chuck

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Ben Hughes · Accepted Answer · 2010-05-14 12:45:00Z

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.

answered May 14, 2010 at 12:45

Ben Hughes

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4 Comments

Chuck Over a year ago

Those are examples of classes within modules, though, while the question is about classes in classes.

Ben Hughes Over a year ago

HTTP doesn't have to be a module. It could be a class depending on how the way you design the program.

user290870 Over a year ago

So it is just a namespace and has no special behavior like, only enclosing class being able to create instances of the enclosed class?

Jörg W Mittag Over a year ago

@user290870: You don't nest classes and modules. You nest constants. Ruby doesn't have nested classes like Beta or Newspeak.

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