Issue #13257 has been reported by Satoshi TAGOMORI.

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Bug #13257: Symbol#respond_to?(:singleton_class) should be false (but true)
https://bugs.ruby-lang.org/issues/13257

* Author: Satoshi TAGOMORI
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin15]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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Objects of some classes doesn't have singleton classes (e.g., Symbol, Integer, Float...).
Symbol#singleton_class raises TypeError.

But Symbol#respond_to?(:singleton_class) returns true, and we cannot know when `#singleton_class` returns a valid class or raise errors in any way (except for calling it).
Symbol#respond_to?(:singleton_class) should return false for such cases. (Integer, Float and other classes without singleton_class too.)



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