Modern Objective-C

Modern Objective-C
Giuseppe Arici

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It’s All About ...

Syntactic Sugar

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Unordered Method
Declarations

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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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Wrong Workaround
In the public interface

- (void)startAudio:(NSError **)error;
@end

NSError *error;
/* ... */
}

@end

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Okay Workaround 1
In a class extension

@interface SongPlayer ()

- (void)startAudio:(NSError **)error;
@end

NSError *error;
/* ... */
}

@end

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Okay Workaround 2
Reorder methods


@end

NSError *error;
/* ... */
}

@end

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Best Solution
Parse the @implementation declarations then bodies


@end

NSError *error;
[self startAudio:&error]; Xcode 4.4+
/* ... */
}

@end

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Enum with Fixed
Underlying Type

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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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Enum with Explicit Type
After OS X v10.5 and iOS
enum {
};

typedef NSUInteger NSNumberFormatterStyle;

• Pro: 32-bit and 64-bit portability

• Con: no formal relationship between type and enum constants

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Enum with Fixed Underlying Type
LLVM 4.2+ Compiler
typedef enum NSNumberFormatterStyle : NSUInteger {
} NSNumberFormatterStyle;
Xcode 4.4+

• Stronger type checking

• Better code completion

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NS_ENUM macro
typedef NS_ENUM(NSUInteger, NSNumberFormatterStyle) {
};
Xcode 4.4+

• Foundation declares like this

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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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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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@Synthesize by
Default

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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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@implementation instance variables

@interface Person : NSObject

@end

@implementation Person {
NSString *_name;
}


@end

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Synthesized instance variables


@end



@end

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@Synthesize by Default
LLVM 4.2+ Compiler


@end

Xcode 4.4+

@end

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Instance Variable Name !?
Instance variables now preﬁxed with “_”


@end

- (NSString *)description {
return _name; Xcode 4.4+
}
/* as if you'd written: @synthesize name = _name; */

@end

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Backward Compatibility !?
Be careful, when in doubt be fully explicit


@end


@synthesize name;
/* as if you'd written: @synthesize name = name; */
@end

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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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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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NSNumbers Literals

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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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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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#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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Boxed Expression
Literals

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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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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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Array Literals

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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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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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Array Creation

NSArray *array;

array = [NSArray array];

array = [NSArray arrayWithObject:a];

array = [NSArray arrayWithObjects:a, b, c, nil];

array = [NSArray arrayWithObjects:objects count:count];

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Array Creation

NSArray *array;

array = @[];

array = @[ a ];

array = @[ a, b, c ];
Xcode 4.4+
array = @[ a, b, c ];

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How Array Literals Work
// when you write this:

NSArray *array = @[ a, b, c ];

// compiler generates:

NSUInteger count = sizeof(objects)/ sizeof(id);
NSArray *array
= [NSArray arrayWithObjects:objects count:count];

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Dictionary Literals

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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 };
dict = [NSDictionary dictionaryWithObjects:objects
forKeys:keys
count:count];

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Dictionary Creation

NSDictionary *dict;

dict = [NSDictionary dictionary];

dict = [NSDictionary dictionaryWithObject:o1 forKey:k1];

dict = [NSDictionary dictionaryWithObjectsAndKeys:
o1, k1, o2, k2, o3, k3, nil];

id keys[] = { k1, k2, k3 };
dict = [NSDictionary dictionaryWithObjects:objects
forKeys:keys
count:count];

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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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How Dictionary Literals Work
// when you write this:

NSDictionary *dict = @{ k1 : o1, k2 : o2, k3 : o3 };

// compiler generates:

id keys[] = { k1, k2, k3 };
NSDictionary *dict =
[NSDictionary dictionaryWithObjects:objects
orKeys:keys
count:count];

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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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Object Subscripting

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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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Array Subscripting
New syntax to access object at index: nsarray[index]

{
}

{ Xcode 4.4+
Song *oldSong = _songs[idx];
_songs[idx] = newSong;
return oldSong;
}
@end

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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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Dictionary Subscripting
New syntax to access object by key: nsdictionary[key]

{
}

{ Xcode 4.4+
id oldObject = _storage[key];
_storage[key] = newObject;
return oldObject;
}
@end

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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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Indexed Subscripting
setObject:atIndexedSubscript:

{
}

{
_songs[idx] = newSong;
return oldSong;
}
@end

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Indexed Subscripting

{
}

{
[_songs setObject:newSong atIndexedSubscript:idx];
return oldSong;
}
@end

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Keyed Subscripting

{
}

{
_storage[key] = newObject;
return oldObject;
}
@end

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Keyed Subscripting

{
}

{
[_storage setObject:newObject forKey:key];
return oldObject;
}
@end

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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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Your Classes Can Be Subscriptable
@interface SongList : NSObject
- (Song *)objectAtIndexedSubscript:(NSUInteger)idx;
- (void) setObject:(Song *)song
atIndexedSubscript:(NSUInteger)idx;
@end

@implementation SongList {
}
- (Song *)objectAtIndexedSubscript:(NSUInteger)idx {
return (Song *)_songs[idx];
}
- (void) setObject:(Song *)song
atIndexedSubscript:(NSUInteger)idx {
_songs[idx] = song;
}
@end

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Summary

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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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Migration
Apple provides a migration tool which is build into
Xcode: Edit Refactor Convert to Modern ...

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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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Modern Objective-C Books

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NSLog(@”Thank you!”);

giuseppe.arici@pragmamark.org

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Modern Objective-C

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