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Feature #2740

closed

Extend const_missing to pass in the nesting

Added by wycats (Yehuda Katz) over 11 years ago. Updated almost 4 years ago.

Status:
Closed
Priority:
Normal
Target version:
[ruby-core:28154]

Description

=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


Files

const_missing_nesting.diff (621 Bytes) const_missing_nesting.diff Patch that provides the nesting to const_missing if arity != 1 wycats (Yehuda Katz), 02/13/2010 08:53 AM
const_missing_murphy.patch (2.56 KB) const_missing_murphy.patch another patch for NoConstantError behavior murphy (Kornelius Kalnbach), 02/16/2010 11:53 AM
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