From: Shugo Maeda <redmine@...>
Date: 2012-03-16T14:42:10+09:00
Subject: [ruby-core:43333] [ruby-trunk - Bug #5544] Lookup scope for class variables in class_eval'd procs changed in 1.9.3


Issue #5544 has been updated by Shugo Maeda.


Joshua Ballanco wrote:
> While I prefer the behavior in 1.9.3 (it is more consistent with constant lookup rules), the inconsistency between 1.9.2 and 1.9.3 is unsettling.

It is intended, so I've fixed the documentation of class_eval.
Please file a feature request ticket if you don't like it.

----------------------------------------
Bug #5544: Lookup scope for class variables in class_eval'd procs changed in 1.9.3
https://bugs.ruby-lang.org/issues/5544#change-24642

Author: Joshua Ballanco
Status: Closed
Priority: Normal
Assignee: Shugo Maeda
Category: core
Target version: 
ruby -v: ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-darwin11.2.0]


When using class_eval with a proc, references to class variables scoped to the receiver in 1.9.2, but in 1.9.3 class variables are now lexically scoped to the environment of the proc. For example, this code:

    class Foo
      def initialize
        @@value = "Set from Foo initialize"
      end
      def report
        @@value
      end
    end
    
    class Bar
      def initialize
        @@value = "Set from Bar initialize"
      end
      def report
        @@value
      end
      def monkey
        Foo.class_eval do
          def set(value)
            @@value = value
          end
        end
      end
    end
    
    b = Bar.new
    b.monkey
    f = Foo.new
    
    puts "Before monkeying:"
    puts "Bar's class var: #{b.report}"
    puts "Foo's class var: #{f.report}"
    
    f.set("Set through Monkey")
    
    puts "After monkeying:"
    puts "Bar's class var: #{b.report}"
    puts "Foo's class var: #{f.report}"

Running under 1.9.2-p290:

    Before monkeying:
    Bar's class var: Set from Bar initialize
    Foo's class var: Set from Foo initialize
    After monkeying:
    Bar's class var: Set from Bar initialize
    Foo's class var: Set through Monkey

Running under 1.9.3-p0:

    Before monkeying:
    Bar's class var: Set from Bar initialize
    Foo's class var: Set from Foo initialize
    After monkeying:
    Bar's class var: Set through Monkey
    Foo's class var: Set from Foo initialize




-- 
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