NSDictionary with 3 key/value pairs. Value sub-expressions of a dictionary literal must be Objective-C object pointer typed, as in array literals. Key sub-expresions must be of an Objective-C object pointer type that implements the <NSCopying> protocol.
+This creates an NSDictionary with 3 key/value pairs. Value sub-expressions of a dictionary literal must be Objective-C object pointer typed, as in array literals. Key sub-expressions must be of an Objective-C object pointer type that implements the <NSCopying> protocol.
+Neither keys nor values can have the value nil in containers. If the compiler can prove that a key or value is nil at compile time, then a warning will be emitted. Otherwise, a runtime error will occur.
Using array and dictionary literals is safer than the variadic creation forms commonly in use today. Array literal expressions expand to calls to +[NSArray arrayWithObjects:count:], which validates that all objects are non-nil. The variadic form, +[NSArray arrayWithObjects:] uses nil as an argument list terminator, which can lead to malformed array objects. Dictionary literals are similarly created with +[NSDictionary dictionaryWithObjects:forKeys:count:] which validates all objects and keys, unlike +[NSDictionary dictionaryWithObjectsAndKeys:] which also uses a nil parameter as an argument list terminator.