From: john mair <redmine@...>
Date: 2011-01-12T20:46:59+09:00
Subject: [ruby-core:34426] [Ruby 1.8-Bug#4273][Open] Inherited hook called after module_eval for Class.new

Bug #4273: Inherited hook called after module_eval for Class.new
http://redmine.ruby-lang.org/issues/show/4273

Author: john mair
Status: Open, Priority: Normal
Category: core, Target version: Ruby 1.8.7
ruby -v: ruby 1.8.7 (2010-06-23 patchlevel 299) [i386-mingw32]

class Base
  def self.inherited(klass)
    klass.instance_variable_set(:@x, :base)
  end
end

Derived = Class.new(Base) do
            @x = :derived
          end

# BUG HERE!
Derived.instance_variable_get(:@x) #=> :base

In Ruby 1.9 the line above returns :derived. Ruby 1.9 has the expected behaviour as the inherited hook should be invoked prior to running the block -- so that the block can override any ivar defaults defined by the inherited hook.

The problem lies in the following code, from object.c:


static VALUE
rb_class_initialize(argc, argv, klass)
    int argc;
    VALUE *argv;
    VALUE klass;
{
    VALUE super;

    if (RCLASS(klass)->super != 0) {
	rb_raise(rb_eTypeError, "already initialized class");
    }
    if (rb_scan_args(argc, argv, "01", &super) == 0) {
	super = rb_cObject;
    }
    else {
	rb_check_inheritable(super);
    }
    RCLASS(klass)->super = super;
    rb_make_metaclass(klass, RBASIC(super)->klass);
*    rb_mod_initialize(klass);
*    rb_class_inherited(super, klass);

    return klass;
}

The fix would be simple, just swap the two starred lines above.

thanks,

John


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