Setter with side effects

person.h

#import <Foundation/Foundation.h>

@interface Person
@property(nonatomic, copy) NSString *firstName;
@property(nonatomic, copy) NSString *lastName;
@property(nonatomic, readonly, strong) NSString *fullName
@end

person.m

#import "person.h"

@interface Person()
// A property can be readonly for the public API, but 
// readwrite internally. Again we do not specifiy copy
// because we are in control of creation of the variable
@property(nonatomic, strong) NSString *fullName;

- (void)updateFullName;
@end

@implementation Person

// Optional synthesize, will be auto synthesized
@synthesize fullName = _fullName;

// Because we are overriding the setters we need to 
// use explicit synthesize
@synthesize firstName = _firstName, lastName = _lastName;

#pragma mark - Overriden property accessor
- (void)setFirstName:(NSString *)firstName {
  if (_firstName != firstName) { // Prevent udpates if the same object is passed again
    _firstName = [firstName copy]; // Copy the value to conform with the property
    
    [self updateFullName]; 
  }
}

- (void)setLastName:(NSString *)lastName {
  if (_lastName != lastName) {
    _lastName = [lastName copy];
    
    [self updateFullName];
  }
}


- (void)updateFullName {
  // No need for copy here stringWithFormat: creates a new string
  self.fullName = [NSString stringWithFormat@"%@ %@", self.firstName, self.lastName];
}

@end