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A Cocoa library to extend the Objective-C programming language.

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The Extended Objective-C library extends the dynamism of the Objective-C programming language to support additional patterns present in other programming languages (including those that are not necessarily object-oriented).

libextobjc is meant to be very modular – most of its classes and modules can be used with no more than one or two dependencies.


libextobjc currently includes the following features:

  • Safe categories, using EXTSafeCategory, for adding methods to a class without overwriting anything already there (identifying conflicts for you).
  • Concrete protocols, using EXTConcreteProtocol, for providing default implementations of the methods in a protocol.
  • Simpler and safer key paths, using EXTKeyPathCoding, which automatically checks key paths at compile-time.
  • Compile-time checking of selectors to ensure that an object declares a given selector, using EXTSelectorChecking.
  • Easier use of weak variables in blocks, using
    , and
    from the EXTScope module.
  • Scope-based resource cleanup, using
    in the EXTScope module, for automatically cleaning up manually-allocated memory, file handles, locks, etc., at the end of a scope.
  • Algebraic data types generated completely at compile-time, defined using EXTADT.
  • Synthesized properties for categories, using EXTSynthesize.
  • Block-based coroutines, using EXTCoroutine.
  • EXTNil, which is like
    , but behaves much more closely to actual
    (i.e., doesn't crash when sent unrecognized messages).
  • Lots of extensions and additional functionality built on top of
    , including extremely customizable method injection, reflection upon object properties, and various functions to extend class hierarchy checks and method lookups.

The experimental branch contains additional features that may be interesting, but are not considered stable or safe for production use. Check out the headers for more information.

Running tests

To execute libextobjc's tests, first run

git submodule update --init --recursive
to bring in the xcconfigs submodule, then open the project file and choose the desired test target.

Adding to your project

If you want to add libextobjc as a dependency to an application, add the repository as a submodule, then include the source files you care about in your Xcode project.

If you want to add libextobjc as a dependency to a framework or library, prefer subtree merging, which will allow you to rename symbols to avoid conflicts, and make any tweaks you need to for your library.

To create a libextobjc subtree:

$ git remote add libextobjc
$ git fetch libextobjc
$ git read-tree --prefix=External/ -u libextobjc/master
$ git reset

Rename any symbols or change whatever you want,

git add
the specific files that you want in your library, and then add them to your Xcode project.

To bring in upstream changes later:

$ git fetch -p libextobjc
$ git merge -Xsubtree=External/ libextobjc/master
$ git reset

Then, again, just add the changes you want.


Released under the MIT License. See the LICENSE file for more information.


libextobjc must be built with ARC enabled, and many of its macros require ARC in the calling files as well. MRR usage is not supported.

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