From: Yehuda Katz <wycats@...>
Date: 2011-12-01T10:36:55+09:00
Subject: [ruby-core:41425] [ruby-trunk - Feature #2740] Extend const_missing to pass in the nesting


Issue #2740 has been updated by Yehuda Katz.


What's the status of this?
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Feature #2740: Extend const_missing to pass in the nesting
http://redmine.ruby-lang.org/issues/2740

Author: Yehuda Katz
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: core
Target version: 2.0.0
ruby -v: ruby 1.8.7 (2008-08-11 patchlevel 72) [universal-darwin10.0] 


=begin
 At the moment, it is impossible for const_missing to differentiate between these cases:
 
     class Foo::Bar
       Baz
     end
  
     class Foo
       class Bar
         Baz
       end
     end
 
 In Rails, we implement a class loading system that loads classes from the file system if they are not found. In the above case, Foo::Baz might be stored in app/models/foo/baz.rb. We would like to be able to use the same Ruby constant lookup logic when looking up classes from the file system.
 
     class Foo::Bar
       Baz
     end
 
 Here, we should look in "app/models/foo/bar/baz.rb" and in "app/models/baz.rb" just as Ruby would search for Foo::Bar::Baz and then Object::Baz.
 
     class Foo
       class Bar
         Baz
       end
     end
 
 Here, we should look in "app/models/foo/bar/baz.rb", then "app/models/foo/baz.rb", and finally "app/models/baz.rb" just as Ruby would search for Foo::Bar::Baz, then Foo::Baz, and then Object::Baz.
 
 In order to achieve this, I propose that we extend the const_missing method to take an optional second parameter containing the nesting:
 
     class Foo
       class Bar
         def self.const_missing(id, nesting)
           id == :Baz
           nesting == [Foo::Bar] # first case
           nesting == [Foo::Bar, Foo] # second case
         end
       end
     end
 
 This would allow people who wish to do their own custom constant loading (such as Rails) to do so in a way that is consistent with Ruby's own constant lookup. In order to avoid backward-compatibility issues, we can check the arity of the const_missing method, and only pass in the nesting if a second parameter was provided.
=end



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