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one-stop-shop for all your method swizzling needs
Objective-C Ruby
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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.


$ cd /path/to/top/of/your/project
$ git submodule add 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 v1.0d0

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.


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.


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


The source code is distributed under the nonviral MIT License. It's the simplest most permissive license available.

Version History

  • v1.0d0: Apr 09 2009: Moved to github.
  • v1.0d0: Dec 28 2007: Under development.
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