Objective-C Fundamentals

Declared properties
109
- (PropertyType)propertyType {
return propertyType;
}
@end
Most of the methods in CTRentalProperty.h are relatively straightforward (for example,
setRentalPrice: B updates the value of an instance variable). One method that
deserves extra attention is setAddress: because it must deal with memory management
issues. Rather than storing the new address in the instance variable directly, it
makes a copy d (taking care to free any previous address first c). This is done so
code similar to the following will work as expected:
NSMutableString *anAddress =
[NSMutableString stringWithString:@"13 Adamson Crescent"];
myRental.address = anAddress;
[anAddress replaceOccurrencesOfString:@"Crescent"
withString:@"Street"
options:NSCaseInsensitiveSearch
range:NSMakeRange(0, [anAddress length])];
NSLog(@"The address is %@", myRental.address);
Most developers would expect this code snippet to indicate the address is 13 Adamson
Crescent even though the string variable is updated to 13 Adamson Street. Making a
copy of the string provided to setAddress: ensures this works as expected. Writing
code to handle conditions like these can get arduous and error prone fairly quickly. It’s
just the kind of thing you let slip toward the end of a late-night, caffeine-aided coding
session. Luckily, Objective-C provides special features to make writing such code easier.
5.4 Declared properties
In listings 5.1 and 5.2, much of the code is related to the declaration and implementation
of getter and setter methods to provide safe access to associated instance variables
and provide extensibility points for future logging or validation. Objective-C can automatically
implement most of the code required to implement these methods using a
feature called Declared Properties.
A property allows you to describe the intent of a setter and getter method pair
while leaving it up to the compiler to provide the actual implementation. This is more
convenient to write and ensures consistent code quality.
5.4.1 @property syntax
The first step in using a property is to declare its presence in the @interface section
of a class. To do this, you use a special @property directive. As an example, you can
declare a property called rentalPrice of type float as follows:
@property float rentalPrice;
You can consider this property declaration as being equivalent to manually declaring
the following two methods:
- (float)rentalPrice;
- (void)setRentalPrice:(float)newRentalPrice;