From: Peter Vandenabeele <peter@...>
Date: 2012-02-14T19:52:44+09:00
Subject: [ruby-core:42611] Re: [ruby-trunk - Bug #6020] Unexpected is_a/kind_of behaviour

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On Tue, Feb 14, 2012 at 11:41 AM, Alex N <masterlambaster@gmail.com> wrote:

>
> Issue #6020 has been updated by Alex N.
>
>
> =begin
> well, at least (({Integer.is_a?(Integer) #=> true})).



TL;DR : use `is_a?` on an _object_ of the class, not on the class itself.

Long version:

The confusion is that is_a? checks if the _object_ is of class Integer,
not the Integer _class_.

So.

$ irb
1.9.3p0 :001 > i = 12
 => 12
1.9.3p0 :002 > i.class
 => Fixnum

i is an _object_ of the Fixnum class.

1.9.3p0 :003 > i.is_a?(Integer)
 => true

yes, the _object_ i is an Integer ...

1.9.3p0 :004 > i.is_a?(Fixnum)
 => true

... and also a Fixnum

1.9.3p0 :005 > Integer.class
 => Class
1.9.3p0 :006 > Integer.is_a?(Integer)
 => false

but the _class_ Integer is not an Integer
(because Class does not inherit from Integer).

1.9.3p0 :007 > Class.ancestors
 => [Class, Module, Object, Wirble::Shortcuts, PP::ObjectMixin, Kernel,
BasicObject]

Class only inherits from Module, Object and BasicObject and mixes in some
additional functionality.

HTH,

Peter


-- 
*** Available for a new project ***

Peter Vandenabeele
http://twitter.com/peter_v
http://rails.vandenabeele.com
http://coderwall.com/peter_v

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<div class=3D"gmail_quote">On Tue, Feb 14, 2012 at 11:41 AM, Alex N <span d=
ir=3D"ltr">&lt;<a href=3D"mailto:masterlambaster@gmail.com">masterlambaster=
@gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
Issue #6020 has been updated by Alex N.<br>
<br>
<br>
=3Dbegin<br>
well, at least (({Integer.is_a?(Integer) #=3D&gt; true})).</blockquote><div=
><br><br>TL;DR : use `is_a?` on an _object_ of the class, not on the class =
itself.<br><br>Long version:<br><br>The confusion is that is_a? checks if t=
he _object_ is of class Integer,<br>
not the Integer _class_.<br><br>So.<br><br>$ irb<br>1.9.3p0 :001 &gt; i =3D=
 12<br>=C2=A0=3D&gt; 12 <br>1.9.3p0 :002 &gt; i.class<br>=C2=A0=3D&gt; Fixn=
um <br><br>i is an _object_ of the Fixnum class.<br><br>1.9.3p0 :003 &gt; i=
.is_a?(Integer)<br>
=C2=A0=3D&gt; true <br><br>yes, the _object_ i is an Integer ...<br><br>1.9=
.3p0 :004 &gt; i.is_a?(Fixnum)<br>=C2=A0=3D&gt; true <br><br>... and also a=
 Fixnum<br><br>1.9.3p0 :005 &gt; Integer.class<br>=C2=A0=3D&gt; Class <br>1=
.9.3p0 :006 &gt; Integer.is_a?(Integer)<br>
=C2=A0=3D&gt; false <br><br>but the _class_ Integer is not an Integer<br>(b=
ecause Class does not inherit from Integer).<br><br>1.9.3p0 :007 &gt; Class=
.ancestors<br>=C2=A0=3D&gt; [Class, Module, Object, Wirble::Shortcuts, PP::=
ObjectMixin, Kernel, BasicObject] <br>
<br>Class only inherits from Module, Object and BasicObject and mixes in so=
me<br>additional functionality.<br><br>HTH,<br><br>Peter<br clear=3D"all"><=
/div></div><br><br>-- <br>*** Available for a new project ***<br>
<br>Peter Vandenabeele<br>
<a href=3D"http://twitter.com/peter_v" target=3D"_blank">http://twitter.com=
/peter_v</a><div><a href=3D"http://rails.vandenabeele.com/" target=3D"_blan=
k">http://rails.vandenabeele.com</a></div><a href=3D"http://coderwall.com/p=
eter_v" target=3D"_blank">http://coderwall.com/peter_v</a><br>


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