Skip to content


Subversion checkout URL

You can clone with
Download ZIP

Fetching latest commit…

Cannot retrieve the latest commit at this time

Failed to load latest commit information.




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 v1.0d1

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.


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

  • v1.0d1: 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.
Something went wrong with that request. Please try again.