On Mon, Feb 1, 2010 at 6:30 AM, Per Bull Holmen <pbhol...@yahoo.com> wrote: > Hi > > I've been playing around with the idea of making a simple bridge between > Objective-C (running under Cocoa) and a script language. Not for the API, > that is, but for user defined classes and methods. For this reason, I'd like > to know whether there are any other ways than NSInvocation to send a message > without knowing arg types and numbers at compile time. Non-hackish ways, that > is. I see that people used objc_msgSendv earlier, but it is no longer > available in Objective-C 2.0. Also, using objc_msgSend doesn't seem to be > platform independent (PPC/Intel). So, does this mean that NSInvocation is the > only civilised way to go? NSInvocation is great, it's just that there's a lot > of overhead, so I assume this is because it has functionality I might not > need?
NSInvocation is the only mechanism provided by Cocoa where you can write code and have it be completely future-proof. Sending an Objective-C message is equivalent to calling a C function, and there's no portable way to do that with arbitrary arguments. NSInvocation handles all the nasty business for you and gives you a nice API. The downside is that it's really slow, as you've seen. My first recommendation would be to look at an existing bridge and see how they do it. Off the top of my head, there's PyObjC, CamelBones, and RubyCocoa. I haven't written a bridge, but here are a few ideas anyway. Since what you ultimately need is fast C function calling with arbitrary arguments, see what's available to do that. I think that libffi is probably your best bet here, although I've never used it. You will have to write more code for this, and possibly encode some platform-specific conventions as well. For example, you need to call the _stret version of objc_msgSend if the function (method) uses struct return calling conventions, but small structs use the normal calling convention, and the boundary between "small" and regular depends on the platform you use. Libffi *may* be able to help you figure out which is which, since it has to know this stuff too. If you really want to go nuts, you can build trampolines at runtime using LLVM. This will give you the speed of native code (once you take the hit of JITting the trampolines), although the complexity of the code gets pretty intense. (It's not as bad as "JIT" might make it sound, but a lot worse than NSInvocation....) If you're interested in this, I have an example where LLVM is put to use for something somewhat similar here: http://www.mikeash.com/?page=pyblog/friday-qa-2009-04-24-code-generation-with-llvm-part-2-fast-objective-c-forwarding.html Mike _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
