From: Matt Mongeau <halogenandtoast@...>
Date: 2013-02-21T06:46:04+09:00
Subject: Re: THE CLASS/OBJECT CHICKEN-AND-EGG PARADOX

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It's not really a paradox. Take for example
irb(main):001:0> a = []
=> []
irb(main):002:0> a << a
=> [[...]]

How can a contain itself? The answer is that it's a reference. This is the
case for Class, the internal structure for determining the class of an
object holds a reference to itself

290  struct RBasic {
 291      unsigned long flags;
 292      VALUE klass;
 293  };

See how klass is a VALUE, in the c-land VALUE is the equivalent of an
Object, so Class is an object where klass is set to point to itself.

You wouldn't really be able to create a class whose superclass is itself in
Ruby (at least nothing I can think of). I think this is often where people
get confused, the c implementation is not under the same restrictions as
the ruby implementation.

Object is in a similar situation:

295  struct RObject {
 296      struct RBasic basic;
 297      struct st_table *iv_tbl;
 298  };

You can see that Object has an RBasic struct inside of it. In class.c you
can see that these cases are handled in a special way.

375     rb_cObject = boot_defclass("Object", rb_cBasicObject);
376     rb_cModule = boot_defclass("Module", rb_cObject);
377     rb_cClass =  boot_defclass("Class",  rb_cModule);

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<div dir=3D"ltr"><div style>It&#39;s not really a paradox. Take for example=
</div><div>irb(main):001:0&gt; a =3D []</div><div>=3D&gt; []</div><div>irb(=
main):002:0&gt; a &lt;&lt; a</div><div>=3D&gt; [[...]]</div><div><br></div>=
<div style>
How can a contain itself? The answer is that it&#39;s a reference. This is =
the case for Class, the internal structure for determining the class of an =
object holds a reference to itself=A0</div><div style><pre class=3D"" style=
=3D"line-height:14px;padding:8px;background-color:rgb(238,238,238);color:rg=
b(0,0,0)">
290  struct RBasic {
 291      unsigned long flags;
 292      VALUE klass;
 293  };</pre></div><div style>See how klass is a VALUE, in the c-land VALU=
E is the equivalent of an Object, so Class is an object where klass is set =
to point to itself.</div><div style><br></div><div style>You wouldn&#39;t r=
eally be able to create a class whose superclass is itself in Ruby (at leas=
t nothing I can think of). I think this is often where people get confused,=
 the c implementation is not under the same restrictions as the ruby implem=
entation.</div>
<div style><br></div><div style>Object is in a similar situation:</div><div=
 style><pre class=3D"" style=3D"line-height:14px;padding:8px;background-col=
or:rgb(238,238,238);color:rgb(0,0,0)">295  struct RObject {
 296      struct RBasic basic;
 297      struct st_table *iv_tbl;
 298  };</pre></div><div style>You can see that Object has an RBasic struct=
 inside of it. In class.c you can see that these cases are handled in a spe=
cial way.</div><div style><br></div><div style><div>375 =A0 =A0 rb_cObject =
=3D boot_defclass(&quot;Object&quot;, rb_cBasicObject);</div>
<div>376 =A0 =A0 rb_cModule =3D boot_defclass(&quot;Module&quot;, rb_cObjec=
t);</div><div>377 =A0 =A0 rb_cClass =3D =A0boot_defclass(&quot;Class&quot;,=
 =A0rb_cModule); =A0 =A0</div></div></div>

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