Issue #13145 has been reported by Tatsuhiro Aoshima.

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Bug #13145: Symbol#clone doesn't work correctly
https://bugs.ruby-lang.org/issues/13145

* Author: Tatsuhiro Aoshima
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin16]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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 Ruby 2.4.0 has a bug that Symbol converted from String at first cannot be cloned:
~~~ ruby
user@mypc ~$ irb
irb(main):001:0> :abc.clone  # When :abc has not been created from String (e.g. 'abc'.to_s.to_sym), clone will work.
=> :abc
irb(main):002:0> 'abc'.to_s.to_sym
=> :abc
irb(main):003:0> :abc.clone  # This clone will also work.
=> :abc
irb(main):004:0> 'abcd'.to_s.to_sym
=> :abcd
irb(main):005:0> :abcd.clone  # This clone WON'T WORK!?
TypeError: allocator undefined for Symbol
	from (irb):5:in `clone'
	from (irb):5
	from /usr/local/bin/irb:11:in `<main>'
irb(main):006:0>
~~~

As written in Ruby 2.4.0 documentation (e.g. https://docs.ruby-lang.org/ja/latest/method/Object/i/clone.html),
Symbol#clone must return itself.

Currently, I define Symbol#clone as the following in order to fix this bug:
~~~ ruby
class Symbol
  def clone
    self
  end
end
~~~
I think something has gone wrong ...



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