From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2013-03-13T06:12:38+09:00
Subject: [ruby-core:53345] [ruby-trunk - Bug #8078][Rejected] Once nil is frozen, an unfrozen instance cannot be reached


Issue #8078 has been updated by marcandre (Marc-Andre Lafortune).

Status changed from Open to Rejected

nil is an immediate. There are no multiple nils; nil.object_id is a constant. Same as true & false.

Any code that checks for `frozen?` and then does a dup might have problems with any Ruby immediate. Note that fixnums & floats are frozen in Ruby 2.0.0. There is `duplicable?` in activesupport for that reason.

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Bug #8078: Once nil is frozen, an unfrozen instance cannot be reached
https://bugs.ruby-lang.org/issues/8078#change-37541

Author: mhuggins (Matt Huggins)
Status: Rejected
Priority: Normal
Assignee: 
Category: core
Target version: 
ruby -v: ruby 1.9.3p327 (2012-11-10) [i386-mingw32]


=begin
This is a rather peculiar bug I stumbled across.  The basic issue is that once `nil` has been frozen, there is no way to access an unfrozen instance of nil.

 nil.frozen?    => false
 nil.freeze
 nil.frozen?    => true

I say this is a peculiar bug because generally it doesn't matter if `nil` is frozen or not (since it is basically frozen even if not explicitly defined as such).  However, since Ruby is based upon duck typing, you might run into a scenario like the following:

 def get(cache_key)
   content = Rails.cache.read(cache_key)
   content.frozen? ? content.dup : content
 end

If I call the above method and the cache key exists, `content` is a frozen string, which I then `dup` to get an unfrozen copy.  If I call the above method and the cache key does NOT exist, `content` is a frozen `nil`, which it then attempts to `dup` unsuccessfully since a NilClass instance cannot be duped.
=end



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