Mac OS X Leopard - ARCAism

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CHAPTER 26 MAC OS X DEVELOPMENT: OBJECTIVE-C
Booleans
In C, there is no Boolean type. In operations, zero is considered false, while anything other than
zero is considered true. Objective-C maintains this convention but adds the scalar type BOOL,
whose values are YES and NO.
Equality
Both C and Objective-C use the = operator for assignment and the == operator to represent
equality. However, since objects in Objective-C are represented by pointers, comparing two
objects with == will not return true unless both are the same pointer.
To work around this problem, NSObject defines the isEqual: method, which compares the
objects’ hash values. Although it’s possible to override isEqual:, it’s not easy, because you also
have to override hash, and hashing is tricky. Plus, it’s often much faster to disqualify equality
based on something like the length of a string or the number of objects in an array than it is to
generate a hash. As such, many classes have their own equality methods, as shown in Table 26-2.
Table 26-2. Class-Specific Equality Methods
Class Method
NSArray isEqualToArray:
NSData isEqualToData:
NSDate isEqualToDate:
NSDictionary isEqualToDictionary:
NSHashTable isEqualToHashTable:
NSIndexSet isEqualToIndexSet:
NSNumber isEqualToNumber:
NSSet isEqualToSet:
NSValue isEqualToValue:
It’s not as bad as sounds. Aside from the rather obvious pattern, Xcode’s autocomplete is
there to help. Whenever you type isEqual, instead of typing the colon and the argument, press the
Esc key. This will open the autocomplete list, and you can see whether a more specific completion
is available.
Void
CAUTION Don’t be fooled by isEqualTo:, which is part of AppleScript and should not be
used directly.
C functions can return nothing by declaring themselves to be of type void and can accept any
pointer by declaring arguments that are pointers to void:
void nothingFromSomething(void *anything)
Void return types and void pointers can also be used in Objective-C:
- (void)nothingFromSomething:(void *)anything;