OBJECTIVE-C keywords

OBJECTIVE-C keywords

OBJECTIVE-C keywords

Objective-C is a superset of C language, so program written in c and C++ should compile as objective-c. It provides some additional keywords, to avoid conflict with keywords in other language it uses ‘@’ at the beginning of keyword. These keyword are called Compiler Directives.

Directives used to declare and define classes, categories and protocols:

• @interface used to declare of class or interface.
•                                 
•  @implementation used to define a class or category.
•  @protocol used to declare a formal protocol.
• @end ends the declaration, definition, category or protocol.
• 
  
• Directive used to specify the visibility of the instance. Default is @protected.
• @private Limits the scope of an instance variable to the class that declares it.
• @protected Limits instance variable scope to declaring and inheriting classes.
• @public Removes restrictions on the scope of instance variables.
• Exception handling directives.
• @try Defines a block within which exceptions can be thrown.
• @throw Throws an exception object.
• @catch Catches an exception thrown within the preceding @try block.
• @finally A block of code that is executed whether exceptions were thrown or not in a @try block.
• Directive used for particular purpose.
• @class Declares the names of classes defined elsewhere.
• @selector(method_name) It returns the compiled selector that identifies method_name.
• @protocol(protocol_name) Returns the protocol_name protocol (an instance of the Protocol class). (@protocol is also valid without (protocol_name) for forward
• declarations.)
• @encode(type_spec) Yields a character string that encodes the type structure of type_spec.
• @"string" Defines a constant NSString object in the current module and
• initializes the object with the specified 7-bit ASCII-encoded string.
• @"string1" @"string2" ...
• @"stringN" Defines a constant NSString object in the currentmodule. The string
• created is the result of concatenating the strings specified in the two
• directives.
• @synchronized() Defines a block of code that must be executed only by one thread
• at a time.