OBJECT-ORIENTED PROGRAMMING

The Objective-C Language

This chapter describes the Objective-C language and discusses the principles of object-oriented programming as they're implemented in Objective-C. It covers all the basic features that the language adds to standard C. The next chapter continues the discussion by taking up more advanced and less commonly used language features.

Objective-C syntax is a superset of standard C syntax, and its compiler works for both C and Objective-C source code. The compiler recognizes Objective-C source files by a ``.m'' extension, just as it recognizes files containing only standard C syntax by a ``.c'' extension. The Objective-C language is fully compatible with ANSI standard C.

Objective-C can also be used as an extension to C++. At first glance, this may seem superfluous since C++ is itself an object-oriented extension of C. But C++ was designed primarily as ``a better C,'' and not necessarily as a full-featured object-oriented language. It lacks some of the possibilities for object-oriented design that dynamic typing and dynamic binding bring to Objective-C. At the same time, it has useful language features not found in Objective-C. When you use the two languages in combination, you can assign appropriate roles to the features found in each and take advantage of what's best in both.

Because object-oriented programs postpone many decisions from compile time to run time, object-oriented languages depend on a run-time system for executing the compiled code. The run-time system for the Objective-C language is discussed in Chapter 4. This chapter and the next present the language, but touch on important elements of the run-time system as they're important for understanding language features. NeXT has modified the GNU C compiler to also compile Objective-C and provides its own run-time system.