The aim of this manual is to introduce you to the Objective-C language and the GNUstep development environment, in particular the Base library. The manual is organised to give you a tutorial introduction to the language and APIs, by using examples whenever possible, rather than providing a lengthy abstract description.
While Objective-C is not a difficult language to learn or use, some of the terms may be unfamiliar, especially to those that have not programmed using an object-oriented programming language before. Whenever possible, concepts will be explained in simple terms rather than in more advanced programming terms, and comparisons to other languages will be used to aid in illustration.
What is Object-Oriented Programming?
There are several object-oriented (OO) programming languages in common use today and you have probably heard of some of them: C++ and Java for example, and of course Objective-C. OO languages all have one thing in common: they allow you to design and write programs in a different way than if you used a traditional procedural language like C or Pascal.
Procedural languages provide the programmer with basic building blocks that consist of data types, (integers, characters, float etc) and functions that act on that data. This forces the program designer to design the program using these same building blocks. Quite often this requires quite a leap in imagination between what the program must do and how it can be implemented.
Object-oriented languages allow the program designer to think in terms of building blocks that are closer to what the program will actually do. Rather than think in terms of data and functions that act on that data, OO languages provide you with objects and the ability to send messages to those objects. Objects are, in a sense, like mini programs that can function on their own when requested by the program or even another object.
For example, an object may exist that can draw a rectangle in a window; all you need to do as a programmer is send the appropriate messages to that object. The messages could tell the object the size of the rectangle and position in the window, and of course tell the object to draw itself. Program design and implementation is now reduced to sending messages to the appropriate objects rather than calling functions to manipulate data.
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