From: George Ogata <g_ogata@...>
Date: 2006-02-04T18:38:19+09:00
Subject: Re: I Broke Ruby (i.e. Missing the Brutally Obvious)

Michael Judge <mjudge@surveycomplete.com> writes:

>   File a.rb
>     require "b"
>
>     class A < Array
>       # Do nothing
>     end
>
>   File b.rb
>     require "a"
>
>     class B < A
>       # Do nothing
>     end
>
> Where's the brutally obvious mistake I made?  Why would A be an 
> uninitialized constant?

Because it hasn't been defined when "class B < A" is evaluated.
Here's what happens, step by step:

- irb evaluates: require "a"
  + ruby parses the 'a.rb' file into an internal representation, doing
    syntax checking along the way
  + ruby evaluates the first expression: require "b"
    * ruby parses the 'b.rb' file into an internal representation,
      doing syntax checking along the way
    * ruby evaluates the first expression: require "a".  As 'a.rb' has
      already been required, this does effectively nothing (see `ri
      require').
    * ruby evaluates the next expression: class B < A ... end.  As A
      is not defined, ruby raises the exception you see.

Why does 'a.rb' require 'b.rb' ?  Circular requires are a bad thing.
You'll need to break it up.

One option is to just have the toplevel file just have a whole
sequence of requires, and have each source file define what it needs
to without messing around with any requires whatsoever.

Hope this helps.