User defined literals in Objective-C
OCUDL is an experiment to bring user defined literals to Objective-C. A literal is a shorthand expression that creates a value of a certain type. For example, 25ul creates an unsigned long of 25, and @”hello” creates an NSString of hello. User defined literals bring this brevity and expressivity to our own types.
Dustin has a post that is well worth reading that describes the details of OCUDL.