From: "Haase, Konstantin" <Konstantin.Haase@...>
Date: 2012-02-14T20:35:06+09:00
Subject: [ruby-core:42615] Re: [ruby-trunk - Bug #6020] Unexpected is_a/kind_of behaviour

> Yes, i know how instance is_a? works.

Apparently not.

	def is_a?(module)
	  self.class.ancestors.include? module
	end

	A.is_a? A # false since Module.ancestors == [Module, Object, Kernel, BasicObject]
	Module.is_a? Module # true since Module.class == Class and Class.ancestors == [Class, Module, Object, Kernel, BasicObject]
	BasicObject.is_a? BasicObject # true since BasicObject.class == Class and Class.ancestors == [Class, Module, Object, Kernel, BasicObject]

Konstantin

On Feb 14, 2012, at 12:23 , Alex N wrote:

> 
> Issue #6020 has been updated by Alex N.
> 
> 
> =begin
> Yes, i know how instance is_a? works. The problem is that the module owns the same functionality as well.
> For example:
> module A; end
> A.class #=> Module
> A.is_a?(A) #=> false
> A.is_a?(A.class) #=> true
> 
> From implementation perspective it's totally ok: Module is not A.
> But (({A.ancestors})) is (({[A]})), meanwhile (({Module.ancestors})) it the whole set of the core objects. At the same time module A is an BasicObject.
> I'm not saying that it's completely wrong, but it feels confusing. On the other had it's really really edge case.
> =end
> 
> ----------------------------------------
> Bug #6020: Unexpected is_a/kind_of behaviour
> https://bugs.ruby-lang.org/issues/6020
> 
> Author: Alex N
> Status: Feedback
> Priority: Low
> Assignee: 
> Category: core
> Target version: 
> ruby -v: ruby 2.0.0dev (2012-02-14 trunk 34598) [x86_64-darwin11.3.0]
> 
> 
> =begin
> I've noticed some inconsistent is_a?/kind_of? methods behavior in a very special cases
> self.class #=> Object
> 
> BasicObject.is_a?(BasicObject) #=> true
> Module.is_a?(Module) #=> true
> Class.is_a?(Class) #=> true
> Object.is_a?(Object) #=> true
> 
> BasicObject.is_a?(Module) #=> true
> 
> Integer.is_a?(Integer) #=> false
> class A; end
> A.is_a?(A) #=> false
> 
> module B; end
> B.is_a?(B) #=> false
> 
> class C < Object; end
> C.is_a?(C) #=> false
> C.is_a?(Object) #=> true
> C.is_a?(BasicObject) #=> true
> C.is_a?(Module) #=> true
> C.is_a?(Class) #=> true
> 
> c = C.new
> c.is_a?(Module) #=> false
> c.is_a?(Class) #=> false
> 
> It looks like it's because Class, Module, Object and BasicObject have class Class, superclass is set properly. 
> Anyway all is logical but not expected. 
> =end
> 
> 
> 
> 
> -- 
> http://bugs.ruby-lang.org/
>