Modern Objective-C introduces several syntactic sugars that simplify working with collections and objects in Objective-C, including array, dictionary and boxed expression literals that avoid explicit constructor methods, as well as object subscripting syntax that allows accessing elements in collections using subscript syntax like nsarray[index]. These features help reduce verbosity and make code more readable while still generating the same underlying method calls as before.

1. Modern Objective-C
Giuseppe Arici
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2. It’s All About ...
Syntactic Sugar
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3. Unordered Method
Declarations
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4. Public & Private Method Ordering
@interface SongPlayer : NSObject
- (void)playSong:(Song *)song;
@end
@implementation SongPlayer
- (void)playSong:(Song *)song {
NSError *error;
[self startAudio:&error];
/* ... */
}
- (void)startAudio:(NSError **)error { /* ... */ }
Warning:
@end
instance method '-startAudio:' not found (return type defaults to 'id')
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5. Wrong Workaround
In the public interface
@interface SongPlayer : NSObject
- (void)playSong:(Song *)song;
- (void)startAudio:(NSError **)error;
@end
@implementation SongPlayer
- (void)playSong:(Song *)song {
NSError *error;
[self startAudio:&error];
/* ... */
}
- (void)startAudio:(NSError **)error { /* ... */ }
@end
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6. Okay Workaround 1
In a class extension
@interface SongPlayer ()
- (void)startAudio:(NSError **)error;
@end
@implementation SongPlayer
- (void)playSong:(Song *)song {
NSError *error;
[self startAudio:&error];
/* ... */
}
- (void)startAudio:(NSError **)error { /* ... */ }
@end
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7. Okay Workaround 2
Reorder methods
@interface SongPlayer : NSObject
- (void)playSong:(Song *)song;
@end
@implementation SongPlayer
- (void)startAudio:(NSError **)error { /* ... */ }
- (void)playSong:(Song *)song {
NSError *error;
[self startAudio:&error];
/* ... */
}
@end
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8. Best Solution
Parse the @implementation declarations then bodies
@interface SongPlayer : NSObject
- (void)playSong:(Song *)song;
@end
@implementation SongPlayer
- (void)playSong:(Song *)song {
NSError *error;
[self startAudio:&error]; Xcode 4.4+
/* ... */
}
- (void)startAudio:(NSError **)error { /* ... */ }
@end
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9. Enum with Fixed
Underlying Type
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10. Enum with Indeterminate Type
Before OS X v10.5 and iOS
typedef enum {
NSNumberFormatterNoStyle,
NSNumberFormatterDecimalStyle,
NSNumberFormatterCurrencyStyle,
NSNumberFormatterPercentStyle,
NSNumberFormatterScientificStyle,
NSNumberFormatterSpellOutStyle
} NSNumberFormatterStyle;
//typedef int NSNumberFormatterStyle;
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11. Enum with Explicit Type
After OS X v10.5 and iOS
enum {
NSNumberFormatterNoStyle,
NSNumberFormatterDecimalStyle,
NSNumberFormatterCurrencyStyle,
NSNumberFormatterPercentStyle,
NSNumberFormatterScientificStyle,
NSNumberFormatterSpellOutStyle
};
typedef NSUInteger NSNumberFormatterStyle;
• Pro: 32-bit and 64-bit portability
• Con: no formal relationship between type and enum constants
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12. Enum with Fixed Underlying Type
LLVM 4.2+ Compiler
typedef enum NSNumberFormatterStyle : NSUInteger {
NSNumberFormatterNoStyle,
NSNumberFormatterDecimalStyle,
NSNumberFormatterCurrencyStyle,
NSNumberFormatterPercentStyle,
NSNumberFormatterScientificStyle,
NSNumberFormatterSpellOutStyle
} NSNumberFormatterStyle;
Xcode 4.4+
• Stronger type checking
• Better code completion
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13. Enum with Fixed Underlying Type
NS_ENUM macro
typedef NS_ENUM(NSUInteger, NSNumberFormatterStyle) {
NSNumberFormatterNoStyle,
NSNumberFormatterDecimalStyle,
NSNumberFormatterCurrencyStyle,
NSNumberFormatterPercentStyle,
NSNumberFormatterScientificStyle,
NSNumberFormatterSpellOutStyle
};
Xcode 4.4+
• Foundation declares like this
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14. Enum with Fixed Underlying Type
Stronger type checking (-Wenum-conversion)
NSNumberFormatterStyle style = NSNumberFormatterRoundUp; // 3
warning:
implicit conversion from enumeration type 'enum
NSNumberFormatterRoundingMode' to different enumeration type
'NSNumberFormatterStyle' (aka 'enum NSNumberFormatterStyle')
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15. Enum with Fixed Underlying Type
Handling all enum values (-Wswitch)
- (void) printStyle:(NSNumberFormatterStyle) style{
switch (style) {
case NSNumberFormatterNoStyle:
break;
case NSNumberFormatterSpellOutStyle:
break;
}
}
warning:
4 enumeration values not handled in switch:
'NSNumberFormatterDecimalStyle',
'NSNumberFormatterCurrencyStyle',
'NSNumberFormatterPercentStyle'...
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16. @Synthesize by
Default
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17. Properties Simplify Classes
@interface instance variables
@interface Person : NSObject {
NSString *_name;
}
@property(strong) NSString *name;
@end
@implementation Person
@synthesize name = _name;
@end
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18. Properties Simplify Classes
@implementation instance variables
@interface Person : NSObject
@property(strong) NSString *name;
@end
@implementation Person {
NSString *_name;
}
@synthesize name = _name;
@end
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19. Properties Simplify Classes
Synthesized instance variables
@interface Person : NSObject
@property(strong) NSString *name;
@end
@implementation Person
@synthesize name = _name;
@end
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20. @Synthesize by Default
LLVM 4.2+ Compiler
@interface Person : NSObject
@property(strong) NSString *name;
@end
@implementation Person
Xcode 4.4+
@end
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21. Instance Variable Name !?
Instance variables now prefixed with “_”
@interface Person : NSObject
@property(strong) NSString *name;
@end
@implementation Person
- (NSString *)description {
return _name; Xcode 4.4+
}
/* as if you'd written: @synthesize name = _name; */
@end
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22. Backward Compatibility !?
Be careful, when in doubt be fully explicit
@interface Person : NSObject
@property(strong) NSString *name;
@end
@implementation Person
@synthesize name;
/* as if you'd written: @synthesize name = name; */
@end
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23. To @Synthesize by Default
• Warning: @Synthesize by Default will not
synthesize a property declared in a protocol
• If you use custom instance variable naming
convention, enable this warning
( -Wobjc-missing-property-synthesis )
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24. Core Data NSManagedObject
Opts out of synthesize by default
/* NSManagedObject.h */
NS_REQUIRES_PROPERTY_DEFINITIONS
@interface NSManagedObject : NSObject {
• NSManagedObject synthesizes properties
• Continue to use @property to declare typed accessors
• Continue to use @dynamic to inhibit warnings
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25. NSNumbers Literals
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26. NSNumber Creation
NSNumber *value;
value = [NSNumber numberWithChar:'X'];
value = [NSNumber numberWithInt:42];
value = [NSNumber numberWithUnsignedLong:42ul];
value = [NSNumber numberWithLongLong:42ll];
value = [NSNumber numberWithFloat:0.42f];
value = [NSNumber numberWithDouble:0.42];
value = [NSNumber numberWithBool:YES];
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27. NSNumber Creation
NSNumber *value;
value = @'X';
value = @42;
value = @42ul;
value = @42ll;
value = @0.42f;
Xcode 4.4+
value = @0.42;
value = @YES;
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28. Backward Compatibility !?
#define YES (BOOL)1 // Before iOS 6, OSX 10.8
#define YES ((BOOL)1) // After iOS 6, OSX 10.8
Workarounds
@(YES) // Use parentheses around BOOL Macros
#if __IPHONE_OS_VERSION_MAX_ALLOWED < 60000
#if __has_feature(objc_bool)
#undef YES
#undef NO // Redefine BOOL Macros
#define YES __objc_yes
#define NO __objc_no
#endif
#endif
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29. Boxed Expression
Literals
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30. Boxed Expression Literals
NSNumber *orientation =
[NSNumber numberWithInt:UIDeviceOrientationPortrait];
NSNumber *piOverSixteen =
[NSNumber numberWithDouble:( M_PI / 16 )];
NSNumber *parityDigit =
[NSNumber numberWithChar:"EO"[i % 2]];
NSString *path =
[NSString stringWithUTF8String:getenv("PATH")];
NSNumber *usesCompass =
[NSNumber numberWithBool:
[CLLocationManager headingAvailable]];
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31. Boxed Expression Literals
NSNumber *orientation =
@( UIDeviceOrientationPortrait );
NSNumber *piOverSixteen =
@( M_PI / 16 );
NSNumber *parityDigit =
@( "OE"[i % 2] );
NSString *path =
@( getenv("PATH") );
Xcode 4.4+
NSNumber *usesCompass =
@( [CLLocationManager headingAvailable] );
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32. Array Literals
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33. Array Creation
More choices, and more chances for errors
NSArray *array;
array = [NSArray array];
array = [NSArray arrayWithObject:a];
array = [NSArray arrayWithObjects:a, b, c, nil];
id objects[] = { a, b, c };
NSUInteger count = sizeof(objects) / sizeof(id);
array = [NSArray arrayWithObjects:objects count:count];
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34. Nil Termination
Inconsistent behavior
// if you write:
id a = nil, b = @"hello", c = @42;
NSArray *array
= [NSArray arrayWithObjects:a, b, c, nil];
Array will be empty
// if you write:
id objects[] = { nil, @"hello", @42 };
NSUInteger count = sizeof(objects)/ sizeof(id);
NSArray *array
= [NSArray arrayWithObjects:objects count:count];
Exception: attempt to insert nil object from objects[0]
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35. Array Creation
NSArray *array;
array = [NSArray array];
array = [NSArray arrayWithObject:a];
array = [NSArray arrayWithObjects:a, b, c, nil];
id objects[] = { a, b, c };
NSUInteger count = sizeof(objects) / sizeof(id);
array = [NSArray arrayWithObjects:objects count:count];
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36. Array Creation
NSArray *array;
array = @[];
array = @[ a ];
array = @[ a, b, c ];
Xcode 4.4+
array = @[ a, b, c ];
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37. How Array Literals Work
// when you write this:
NSArray *array = @[ a, b, c ];
// compiler generates:
id objects[] = { a, b, c };
NSUInteger count = sizeof(objects)/ sizeof(id);
NSArray *array
= [NSArray arrayWithObjects:objects count:count];
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38. Dictionary Literals
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39. Dictionary Creation
More choices, and more chances for errors
NSDictionary *dict;
dict = [NSDictionary dictionary];
dict = [NSDictionary dictionaryWithObject:o1 forKey:k1];
dict = [NSDictionary dictionaryWithObjectsAndKeys:
o1, k1, o2, k2, o3, k3, nil];
id objects[] = { o1, o2, o3 };
id keys[] = { k1, k2, k3 };
NSUInteger count = sizeof(objects) / sizeof(id);
dict = [NSDictionary dictionaryWithObjects:objects
forKeys:keys
count:count];
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40. Dictionary Creation
NSDictionary *dict;
dict = [NSDictionary dictionary];
dict = [NSDictionary dictionaryWithObject:o1 forKey:k1];
dict = [NSDictionary dictionaryWithObjectsAndKeys:
o1, k1, o2, k2, o3, k3, nil];
id objects[] = { o1, o2, o3 };
id keys[] = { k1, k2, k3 };
NSUInteger count = sizeof(objects) / sizeof(id);
dict = [NSDictionary dictionaryWithObjects:objects
forKeys:keys
count:count];
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41. Dictionary Creation
NSDictionary *dict;
dict = @{};
dict = @{ k1 : o1 }; // key before object
dict = @{ k1 : o1, k2 : o2, k3 : o3 };
Xcode 4.4+
dict = @{ k1 : o1, k2 : o2, k3 : o3 };
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42. How Dictionary Literals Work
// when you write this:
NSDictionary *dict = @{ k1 : o1, k2 : o2, k3 : o3 };
// compiler generates:
id objects[] = { o1, o2, o3 };
id keys[] = { k1, k2, k3 };
NSUInteger count = sizeof(objects) / sizeof(id);
NSDictionary *dict =
[NSDictionary dictionaryWithObjects:objects
orKeys:keys
count:count];
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43. Container Literals Restriction
All containers are immutable, mutable use: -mutableCopy
NSMutableArray *mutablePragmers =
[@[ @"Fra", @"Giu", @"Mat", @"Max", @"Ste" ] mutableCopy];
For constant containers, simply implement +initialize
static NSArray *thePragmers;
+ (void)initialize {
if (self == [MyClass class]) {
thePragmers =
@[ @"Fra", @"Giu", @"Mat", @"Max", @"Ste" ];
}
}
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44. Object Subscripting
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45. Array Subscripting
New syntax to access object at index: nsarray[index]
@implementation SongList
{
NSMutableArray *_songs;
}
- (Song *)replaceSong:(Song *)newSong
atIndex:(NSUInteger)idx
{
Song *oldSong = [_songs objectAtIndex:idx];
[_songs replaceObjectAtIndex:idx withObject:newSong];
return oldSong;
}
@end
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46. Array Subscripting
New syntax to access object at index: nsarray[index]
@implementation SongList
{
NSMutableArray *_songs;
}
- (Song *)replaceSong:(Song *)newSong
atIndex:(NSUInteger)idx
{ Xcode 4.4+
Song *oldSong = _songs[idx];
_songs[idx] = newSong;
return oldSong;
}
@end
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47. Dictionary Subscripting
New syntax to access object by key: nsdictionary[key]
@implementation Database
{
NSMutableDictionary *_storage;
}
- (id)replaceObject:(id)newObject
forKey:(id <NSCopying>)key
{
id oldObject = [_storage objectForKey:key];
[_storage setObject:newObject forKey:key];
return oldObject;
}
@end
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48. Dictionary Subscripting
New syntax to access object by key: nsdictionary[key]
@implementation Database
{
NSMutableDictionary *_storage;
}
- (id)replaceObject:(id)newObject
forKey:(id <NSCopying>)key
{ Xcode 4.4+
id oldObject = _storage[key];
_storage[key] = newObject;
return oldObject;
}
@end
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49. How Subscripting Works
iOS 6
Array Style: Indexed subscripting methods OSX 10.8
- (elementType)objectAtIndexedSubscript:(indexType)idx
- (void)setObject:(elementType)obj
atIndexedSubscript:(indexType)idx;
elementType must be an object pointer, indexType must be integral
iOS 6
Dictionary Style: Keyed subscripting methods OSX 10.8
- (elementType)objectForKeyedSubscript:(keyType)key;
- (void)setObject:(elementType)obj
forKeyedSubscript:(keyType)key;
elementType and keyType must be an object pointer
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50. Indexed Subscripting
setObject:atIndexedSubscript:
@implementation SongList
{
NSMutableArray *_songs;
}
- (Song *)replaceSong:(Song *)newSong
atIndex:(NSUInteger)idx
{
Song *oldSong = _songs[idx];
_songs[idx] = newSong;
return oldSong;
}
@end
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51. Indexed Subscripting
setObject:atIndexedSubscript:
@implementation SongList
{
NSMutableArray *_songs;
}
- (Song *)replaceSong:(Song *)newSong
atIndex:(NSUInteger)idx
{
Song *oldSong = _songs[idx];
[_songs setObject:newSong atIndexedSubscript:idx];
return oldSong;
}
@end
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52. Keyed Subscripting
setObject:atIndexedSubscript:
@implementation Database
{
NSMutableDictionary *_storage;
}
- (id)replaceObject:(id)newObject
forKey:(id <NSCopying>)key
{
id oldObject = _storage[key];
_storage[key] = newObject;
return oldObject;
}
@end
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53. Keyed Subscripting
setObject:atIndexedSubscript:
@implementation Database
{
NSMutableDictionary *_storage;
}
- (id)replaceObject:(id)newObject
forKey:(id <NSCopying>)key
{
id oldObject = _storage[key];
[_storage setObject:newObject forKey:key];
return oldObject;
}
@end
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54. Backward Compatibility !?
To deploy back to iOS 5 and iOS 4 you need ARCLite:
use ARC or set explicit linker flag: “-fobjc-arc”
To make compiler happy, you should add 4 categories:
#if __IPHONE_OS_VERSION_MAX_ALLOWED < 60000
@interface NSDictionary(BCSubscripting)
- (id)objectForKeyedSubscript:(id)key;
@end
@interface NSMutableDictionary(BCSubscripting)
- (void)setObject:(id)obj forKeyedSubscript:(id )key;
@end
@interface NSArray(BCSubscripting)
- (id)objectAtIndexedSubscript:(NSUInteger)idx;
@end
@interface NSMutableArray(BCSubscripting)
- (void)setObject:(id)obj atIndexedSubscript:(NSUInteger)idx;
@end
#endif
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55. Your Classes Can Be Subscriptable
@interface SongList : NSObject
- (Song *)objectAtIndexedSubscript:(NSUInteger)idx;
- (void) setObject:(Song *)song
atIndexedSubscript:(NSUInteger)idx;
@end
@implementation SongList {
NSMutableArray *_songs;
}
- (Song *)objectAtIndexedSubscript:(NSUInteger)idx {
return (Song *)_songs[idx];
}
- (void) setObject:(Song *)song
atIndexedSubscript:(NSUInteger)idx {
_songs[idx] = song;
}
@end
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56. Summary
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57. Availability
Feature Xcode 4.4+ iOS 6 OSX 10.8
Unordered Method Declarations ✓
Enum With Fixed Underlying Type ✓
@Synthesize by Default ✓
NSNumbers Literals ✓
Boxed Expression Literals ✓
Array Literals ✓
Dictionary Literals ✓
Object Subscripting ✓ ✓*
* Partially Required
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58. Migration
Apple provides a migration tool which is build into
Xcode: Edit Refactor Convert to Modern ...
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59. Demo
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60. Modern Objective-C References
• Clang: Objective-C Literals
• Apple: Programming with Objective-C
• WWDC 2012 – Session 405 – Modern Objective-C
• Mike Ash: Friday Q&A 2012-06-22: Objective-C Literals
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61. Modern Objective-C Books
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62. NSLog(@”Thank you!”);
giuseppe.arici@pragmamark.org
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