Cocoa mail archive
Re: Strategies to prevent class name clashes
FROM : Jens Alfke
DATE : Sat Feb 16 17:42:27 2008
On 15 Feb '08, at 3:42 AM, Arne Scheffler wrote:
> the toolkit in question is VSTGUI. It's a C++ cross-platform UI
> library. It is statically linked into every plug-in. Mostly the
> users of it won't use Objective-C by them self.
> The problem I did face was that I have an ivar which is a C++ class
> of the lib. And when I used this ivar and the C++ object had a
> different layout than at build time it crashed.
I'm confused — is this a problem of collisions between C++ classes or
Obj-C classes?
If the C++ code is statically linked into each plugin, then it can't
conflict between multiple plugins. Each one will be directly calling
its own copy of the code, even if the C++ classnames and namespaces
are the same.
Objective-C classes _will_ conflict between multiple plugins, if they
have the same name. So what you have to do is make sure that every
plugin that statically links shared Obj-C code renames the classes
with unique prefixes. Basically, any time you write an Obj-C bundle or
framework, all the classes in it need to have a unique prefix, whether
or not you wrote those classes yourself.
It sounds like what's happening to you is that some of your classes
load out of your bundle and some get loaded from another plugin, and
these mismatched classes are passing C++ object pointers between
themselves. So when code from one plugin allocates a C++ object (with
one version of the C++ code), and then code from a different plugin
receives a pointer to that object and tries to operate on it using a
different version of the C++ code, you go boom.
But that's not a C++ specific problem. As soon as you have parts of
different versions of a library loaded and calling into each other,
there will be trouble. I've had this happen with Obj-C and pure C code
as well. You have to uniquify your Obj-C class names to avoid this.
—Jens_______________________________________________
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DATE : Sat Feb 16 17:42:27 2008
On 15 Feb '08, at 3:42 AM, Arne Scheffler wrote:
> the toolkit in question is VSTGUI. It's a C++ cross-platform UI
> library. It is statically linked into every plug-in. Mostly the
> users of it won't use Objective-C by them self.
> The problem I did face was that I have an ivar which is a C++ class
> of the lib. And when I used this ivar and the C++ object had a
> different layout than at build time it crashed.
I'm confused — is this a problem of collisions between C++ classes or
Obj-C classes?
If the C++ code is statically linked into each plugin, then it can't
conflict between multiple plugins. Each one will be directly calling
its own copy of the code, even if the C++ classnames and namespaces
are the same.
Objective-C classes _will_ conflict between multiple plugins, if they
have the same name. So what you have to do is make sure that every
plugin that statically links shared Obj-C code renames the classes
with unique prefixes. Basically, any time you write an Obj-C bundle or
framework, all the classes in it need to have a unique prefix, whether
or not you wrote those classes yourself.
It sounds like what's happening to you is that some of your classes
load out of your bundle and some get loaded from another plugin, and
these mismatched classes are passing C++ object pointers between
themselves. So when code from one plugin allocates a C++ object (with
one version of the C++ code), and then code from a different plugin
receives a pointer to that object and tries to operate on it using a
different version of the C++ code, you go boom.
But that's not a C++ specific problem. As soon as you have parts of
different versions of a library loaded and calling into each other,
there will be trouble. I've had this happen with Obj-C and pure C code
as well. You have to uniquify your Obj-C class names to avoid this.
—Jens_______________________________________________
Cocoa-dev mailing list (<email_removed>)
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Contact the moderators at cocoa-dev-admins(at)lists.apple.com
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