From: Peter <peter.c.r.lane@...>
Date: 2010-09-01T19:30:16+09:00
Subject: Re: Ruby constant lookup for classes in modules

On Sep 1, 1:09 am, Jack Christensen <j...@jackchristensen.com> wrote:
>   What's the difference between defining a class inside of a module and
> using the module as a prefix?
>
> module Foo
>    class Bar
>    end
> end
>
> module Foo
>    class Works
>      def f
>        Bar.new
>      end
>    end
> end
>
> class Foo::Fails
>    def f
>      Bar.new
>    end
> end
>
> Foo::Works.new.f
> Foo::Fails.new.f
>
> The last line fails:
>
> lookup.rb:16:in `f': uninitialized constant Foo::Fails::Bar (NameError)
>      from lookup.rb:21
>
> I would have thought that both ways of placing a class in a module would
> be equivalent.
>
> Thanks.
>
> Jack

Hi Jack,

I believe the difference is one of scope:

module Foo
  class Works

means "put Works in the namespace of Foo" and "define Works in the
scope of the module Foo", and hence 'Bar' is accessible.

class Foo::Fails

means, "put Fails in the namespace of Foo" but "define Fails in the
current scope", and hence 'Bar' is not accessible.

Hope that helps,

  Peter.