From: Jeremy Henty <jeremy@...>
Date: 2007-02-20T18:30:12+09:00
Subject: Re: Why should initialize_copy verify the class of the original?

On 2007-02-19, David Vallner <david@vallner.net> wrote:
> On Sun, 18 Feb 2007 17:10:06 +0100, Jeremy Henty <jeremy@chaos.org.uk>  
> wrote:
>
>> [...] If #initialize_copy is only called from inside #dup or #clone
>> then surely the receiver has to be of the same class as the
>> original!  What am I missing?
>
> CDPlayer.new.instance_eval {initialize_copy(TeddyBear.new)}

That's the conclusion we came to in the other thread (though it wasn't
written down explicitly as you did here).

> Which would probably cause the C implementation to do Bad Things
> without said check.

Yes, if the instances of the CDPlayer and TeddyBear classes are T_DATA
objects that wrap (CDPlayer *) and (TeddyBear *) pointers, then this
code will coerce a (TeddyBear *) to a (CDPlayer *).  Hilarity may well
ensue.

Incidentally the Pickaxe is (IMHO) a little misleading on this point,
it describes Data_Get_Struct as "a type-safe wrapper around the macro
DATA_PTR(obj)".  In fact it's only type-safe with respect to the TYPE
of obj , it's not type-safe with respect to the type of the C pointer
that obj wraps.

Regards, 

Jeremy Henty