Developer John Holdsworth set up a small site ( _from which it’s possible to download a pre-release version of Injection for Xcode.

Using Injection it’s possible to make a change to the implementation of an Objective-C class and have it take effect as soon as the class is saved without having to restart an application. This works for OS X and iOS applications in the simulator and on iOS devices.

Injection works by converting your classes into categories using a small set of preprocessor macros. This category can then be loaded at run time using a bundle. As Objective-C “binds” at runtime, it will always chose the new implementation of the class over that which the application was last built with.

Injection is free to evaluate for two weeks. After this you’ll be prompted to buy the application the next time it starts.