Objective-C
Objective-C is an object-oriented superset of the derived from::compatible with::C language. It mostly copies the message passing system from derived from::Smalltalk. It was popularized by NeXT, and then again by Apple Inc with Mac OS X and iOS to implement the Cocoa frameworks. Its main reference implementation is within the gcc compiler, maintained mostly by Apple.
As of October 2011, with the release of XCode 4.2, Apple switched from gcc to Clang as its default compiler. Clang/LLVM offers competitive execution times, better compile times, improved error messages, and supports a simpler alternative syntax for expressing NSArray & NSDictionary literals and indexing. In the same release Apple also introduced automatic reference counting (ARC) which eliminates the need to manually release/retain memory. With ARC the compiler reports an error any time it encounters a call to release, autorelease, retain, or dealloc.
The release of Xcode 4.4 (4.5 for iOS) added syntax to specify literals for NSArray, NSDictionary, NSNumber, and NSString, as well as subscript syntax to access elements of NSArray and NSDictionary.
Unless otherwise stated, Objective-C code samples will assume that they are compiled with ARC enabled, and that the compiler supports Objective-C literals and Blocks.
For details of how to compile and run examples of Rosetta Code tasks written in Objective C under Linux or Windows see GNUstep