From: "Michael T. Richter" <ttmrichter@...>
Date: 2008-07-23T22:03:59+09:00
Subject: Re: circular 'require'

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On Wed, 2008-07-23 at 20:39 +0900, Calamitas wrote: 

> test1.rb is executed twice, but what probably caused the error in the
> OP's original program (the OP pared it down to a point where it
> actually did "work") is the fact that "the rest of test1.rb" is
> executed before "the rest of test2.rb". It can probably be solved by
> doing "ruby -r test1.rb" instead, but that's icky. Generally, if I
> *were* to use circular requires, I'd never put "executable code" in
> either file, just "declarations". I don't use them though. Not anymore
> after I've been bitten a few times.


Here's what the OP was talking about, I suspect, taken down to its
briefest possible example:


        $ cat test1.rb
        require 'test2'
        class NeededInTest2
          @@funny_stuff = NeededInTest1.new
        end
        
        michael@isolde:~/junk$ cat test2.rb
        require 'test1'
        class NeededInTest1
          @@funny_stuff = NeededInTest2.new
        end
        
        michael@isolde:~/junk$ ruby test1.rb
        ./test1.rb:3: uninitialized constant NeededInTest2::NeededInTest1 (NameError)
        	from /home/michael/software/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require'
        	from /home/michael/software/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
        	from ./test2.rb:1
        	from /home/michael/software/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require'
        	from /home/michael/software/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
        	from test1.rb:1


This is the problem boiled down to its essence.  There is no easy way
out of this either that doesn't either a) mangle the architecture or b)
fail.  You can't use something like C/++'s "include guards" to get
around this, nor can you use any kind of super-class elevation trick or
the like.  What would be needed to solve this issue would be for ruby to
have a proper sense of modules and do linkage across those instead of
treating the entire tree of requires as, in effect, one ginormous text
file.

-- 
Michael T. Richter <ttmrichter@gmail.com> (GoogleTalk:
ttmrichter@gmail.com)
Theory is knowledge that doesn't work. Practice is when everything works
and you don't know why. (Hermann Hesse)

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