Description
JRSwizzle is source code package that offers a single, easy, correct+consistent interface for exchanging Objective-C method implementations ("method swizzling") across many versions of Mac OS X, Objective-C and runtime architectures.
More succinctly: JRSwizzle wants to be your one-stop-shop for all your method swizzling needs.
Download
JRSwizzle is still under development (set the open tickets) -- when it's ready I'll offer a .zip download link. Until then browse the latest source or check it out with svn co http://rentzsch.com/svn/trunk/cocoa/JRSwizzle.
Reason for Existence
- Easy: Just do this: [SomeClass jr_swizzle:@selector(foo) withMethod:@selector(my_foo) error:&error]; Voila.
- Correct: There's a subtle interaction between method swizzling and method inheritance. Following in Kevin Ballard's footsteps, this package Does The Right Thing.
- Compatible: JRSwizzle should Just Work on any version of Mac OS X you care about. Here's the exhaustive compatibility list:
- Mac OS X v10.3/ppc (Ballard implementation)
- Mac OS X v10.4/ppc (Ballard implementation)
- Mac OS X v10.4/i386 (Ballard implementation)
- Mac OS X v10.5/ppc (method_exchangeImplementations+Ballard implementation)
- Mac OS X v10.5/i386 (method_exchangeImplementations+Ballard implementation)
- Mac OS X v10.5/ppc64 (method_exchangeImplementations+Ballard implementation)
- Mac OS X v10.5/x86_64 (method_exchangeImplementations+Ballard implementation)
- Robust: All parameters are checked and JRSwizzle returns an optional NSError with high-quality diagnostics.
Comparison
There's at least four swizzling implementations floating around. Here's a comparison chart to help you make sense of how they relate to each other and why JRSwizzle exists.
| Scenario | Swizzle Technology | Method Implementation | Correct Behavior | 10.4 | 64-bit |
| 1 | Classic | Direct | YES | YES | NO |
| 2 | Classic | Inherited | NO | YES | NO |
| 3 | Ballard | Direct | YES | YES | NO |
| 4 | Ballard | Inherited | YES | YES | NO |
| 5 | Apple | Direct | YES | NO | YES |
| 6 | Apple | Inherited | NO | NO | YES |
| 7 | JRSwizzle | Direct | YES | YES | YES |
| 8 | JRSwizzle | Inherited | YES | YES | YES |
- Classic is the canonical MethodSwizzle() implementation as described in CocoaDev's MethodSwizzling page.
- Ballard is Kevin Ballard's improved implementation which solves the inherited method problem.
- Apple is 10.5's new method_exchangeImplementations API.
- JRSwizzle is this package.
License
The source code is distributed under the nonviral MIT License. It's the simplest most permissive license available.
Version History
- v1.0d0: Dec 28 2007: Under development.
