I see people have forked this so I figured I should add some information.

The only changes I've made to my knowledge were small ones to make it work on an iOS device. Use at your own risk! Below was the original README.

JRSwizzle

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

$ cd /path/to/top/of/your/project
$ git submodule add git://github.com/rentzsch/jrswizzle.git JRSwizzle
$ git submodule init && git submodule update

# OPTIONAL: Execute the following commands if you want to explicitly peg
# to a certain version. Otherwise `git submodule update` will keep you
# current with HEAD.

$ cd JRSwizzle
$ git checkout v1.0d1

Reasons 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.

Support

Please use JRSwizzle's Lighthouse project site to file bugs or feature requests.

To contribute, please fork this project, make+commit your changes and then send me a pull request.

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

• v1.0d1: May 31 2009

  • [FIX] Soothe valgrind by nulling out hoisted_method_list->obsolete, which it apparently reads. (Daniel Jalkut)

  • [FIX] Xcode 3.2 apparently now needs ARCHS set explicitly for 10.3 targets. (rentzsch)

• v1.0d0: Apr 09 2009

  • Moved to github.

• v1.0d0: Dec 28 2007

  • Under development.