Mac OS X Leopard - ARCAism

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CHAPTER 26 MAC OS X DEVELOPMENT: OBJECTIVE-C
hue, and, uh . . . needless to say, most programmers spend a lot of time looking up functions to
remember how to write them, let alone ever trying to read them. Now, consider the same thing
as an Objective-C method:
[myObject setColorWithRed:0.4 green:0.3 blue:0.0 alpha:1.0];
It’s pretty clear what each of the arguments mean, whether you’re writing the code for the
first time or you’re reading someone else’s code three years down the line.
A method’s prototype is equally readable, outlining not only the meaning of the method
parameters but also their types, the return type, and whether the method belongs to the class or
its individual instances:
- (void)setColorWithRed:(CGFloat)red green:(CGFloat)green blue:(CGFloat)blue
alpha:(CGFloat)alpha;
This method is of type void, so it returns nothing. All its arguments are of type CGFloat. As
detailed in this chapter, CGFloat is a width-neutral floating-point scalar that is converted at compile
time into a float on 32-bit systems or a double on 64-bit systems. In this case, the method is
an instance method, as indicated by the starting -. Class methods start with +.
This method is, for all intents and purposes, identical to the following function:
void setColor(CGFloat red, CGFloat green, CGFloat blue, CGFloat alpha);
As would be expected, pointers to objects are represented with the * operator. For example,
a class method that took an argument of type NSNumber and returned an NSString would look
like this:
+ (NSString *)stringWithNumber:(NSNumber *)number;
Objective-C Improves C
Although C has its own compiler directives, using the # prefix, Objective-C introduces a new set
of its own, using the @ prefix. This is an artifact of Objective-C’s origins as a C preprocessor but
continues to serve as a convenient sigil of which features are part of Objective-C and which features
are just plain C.
Objective-C separates interface from implementation but does so at the preprocessor level
with the directives @interface, @implementation, and @end. This allows the use of separate header
and implementation files but also allows multiple classes to be defined in a single file, as appropriate.
Finally, many parts of the C standard library have new, upgraded versions in Cocoa that
should be used instead. The older C features are still there, and the two can be intermixed.
Memory Management
Object life cycles and interaction complicate memory management, so the entire C memory system
has been abstracted. Although malloc and free are still there, they’re not used. Instantiation
in Objective-C is actually a four-step process: declaration, assignment, allocation, and initialization.
These are usually done on one line:
NSObject *object = [[NSObject alloc] init];