Bug #5828: Non anonymous classes can't be frozen, cloned and then inspected

• Status: Closed
• Assignee: akr (Akira Tanaka)
• Target version: -
• ruby -v: ruby 2.0.0dev (2011-11-27 trunk 33860) [x86_64-darwin10.8.0]

[agrimm (Andrew Grimm)]

=begin
If you assign a class to a constant (that is, it isn't anonymous), and you freeze it and then clone it, you can't call to_s on it.

MyClass = Class.new ; MyClass.freeze.clone.to_s
RuntimeError: can't modify frozen Class
	from (irb):1:in `to_s'
	from (irb):1
	from /Users/agrimm/.rvm/rubies/ruby-head/bin/irb:16:in `<main>'

MyConstantObject = Object.new ; MyConstantObject.freeze.clone.to_s # => "#<Object:0x00000100884d60>"
MyClass_2 = Class.new ; MyClass_2.clone.to_s # => "#<Class:0x00000100872930>"
MyClass_3 = Class.new ; MyClass_3.freeze.to_s # => "MyClass_3" 
MyClass_4 = Class.new.freeze ; MyClass_4.clone.to_s # => "#<Class:0x0000010088d4d8>" 
MyClass_5 = Class.new.freeze ; MyClass_5.freeze.clone.to_s # => An exception
local_variable_class = Class.new ; local_variable_class.freeze.clone.to_s # => "#<Class:0x00000100964028>" 

Presumably this is caused by class only determining whether it's assigned to a constant when it's first inspected.

I don't have a use case for freezing and cloning a class.
=end

[ko1 (Koichi Sasada)]

• Assignee set to akr (Akira Tanaka)

Tanaka-san says he found the reason of this issue.

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned

[akr (Akira Tanaka)]

• Status changed from Assigned to Feedback

The name of anonymous class is searched and cached when it is first inspected.
The cache is implemented as a hidden instance variable of the class.
If the class is frozen, the cache is failed as the exception because the instance variable is not assignable.

Note that Class.new.freeze.to_s doesn't raise the exception.
This is because Kernel#freeze is redefined by Module#freeze and it caches the class name before freezing.

Kernel#clone is not redefined.
So there is not such trick to avoid the exception.

I'm not sure that it is worth to fix this problem.

[agrimm (Andrew Grimm)]

I'm happy for this bug to be closed, as I don't have a need to freeze and clone a class.

[akr (Akira Tanaka)]

• Status changed from Feedback to Closed
• % Done changed from 0 to 100

Applied in changeset r46370.

---

• object.c (rb_mod_initialize_clone): Override Kernel#initialize_clone
  to avoid an exception on Class.new.freeze.clone.to_s.
  Reported by Andrew Grimm. [ruby-core:41858] [Bug #5828]

[akr (Akira Tanaka)]

I decided to fix this problem because to_s method is useful for debugging and exception on to_s can be
irritating.