TAILIEUCHUNG - HandBooks Professional Java-C-Scrip-SQL part 107

Tham khảo tài liệu 'handbooks professional java-c-scrip-sql part 107', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Type qualifiers Type qualifiers go before a C or Objective-C type in a method declaration and modify that type. Supported qualifiers are in oneway out bycopy inout byref These qualifiers can only be used in formal protocols and implementations not in class or category declarations. They specify how parameters are to be passed when you are using remote messaging. Type qualifiers can be combined although not all combinations make sense. They are discussed at greater length in Section . Predefined Types Constants and Variables Objective-C adds the special type id which is generic like a void in C but which does not preclude you from sending messages. In addition the Objective-C environment provides some C types constants and variables to support object-oriented programming. Types Along with class types that you define Objective-C introduces these built-in types you can use when declaring variables id A generic Objective-C object pointer type. You can send any message to the variables of this type without compiler warnings. See Section . At runtime the receiver may handle the message delegate it or explicitly ignore it. If it does none of these a runtime exception occurs. See Section . Unspecified method return or parameter types default to id. The name id is a C typedef for a pointer to a structure with one member a field that points to a class object. Section discusses this at greater length. Class A pure C type a pointer to an Objective-C class structure. The runtime system contains a structure for each Objective-C class in your program s code. Calling the -class method of any object returns a value of this type. MetaClass Provided in the GNU runtime but not in Darwin this is identical to Class. It s used for clarity when operating with metaclass objects. Protocol An Objective-C class. The runtime system contains an instance for each Objective-C protocol that is either adopted by a class in your program s code or referred to in

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