Re: @property problem
Re: @property problem
- Subject: Re: @property problem
- From: Jean-Daniel Dupas <email@hidden>
- Date: Sun, 17 Feb 2008 20:18:47 +0100
Le 17 févr. 08 à 19:52, William Squires a écrit :
On Feb 17, 2008, at 12:03 PM, Bill Bumgarner wrote:
On Feb 17, 2008, at 9:47 AM, William Squires wrote:
On Feb 17, 2008, at 11:13 AM, Jim Correia wrote:
On Feb 17, 2008, at 11:59 AM, William Squires wrote:
But it doesn't answer the question. Why even make the change in
the 64-bit runtime? This would seem to hide a source of bugs, by
taking the responsibility for providing storage away from the
programmer. Some storage is still necessary.
As it stands, you cannot add iVars to a base class in the 32-bit
runtime without required that all subclasses be recompiled.
??? Why should the subclasses know anything about the base class
other than what the base class exposes in its API (from the POV of
whomever is writing the subclass code, if they follow proper OO
methodologies)? Only if I rewrite the subclass to specifically use
the new iVar should I need to recompile it.
i.e. If I have a base class A
It is an implementation detail.
In the legacy -- 32 bit -- runtime, each subclass effectively tacks
its instance variables onto the end of the superclass's instance
variables as if it were all one big extensible C structure. If the
superclass adds an ivar, the offset of the ivars in said structure
are thus incorrect and, unless you recompile, subclasses will read/
write from the wrong spot in memory and *boom*.
The modern -- 64 bit -- runtime fixes this particular issue.
Okay, that explains it - weird... I wonder why ObjC did that?
That's not an obj-c issue. That's a runtime and compiler issue. If you
want to know why the OS X runtime did that, you will have to go back
to the NeXT's days.
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