The document discusses 5 ways to improve Objective-C code while still using Objective-C. It covers: 1) Adding nullability to method parameters and returns to reduce null errors, 2) Using constants to increase predictability, 3) Enforcing designated initializers to ensure objects are initialized correctly, 4) Managing weak references to prevent issues with delegates being released, and 5) Using static analysis to catch nullability and other issues. The overall message is that small changes can make Objective-C code more robust and predictable without needing to rewrite it in another language.

1. to the next level
John Sundell
Lead iOS Developer, Spotify
@johnsundell
Objective-CTaking

2. Objective-C ?

4. I ❤

5. Sometimes you
can’t use it :(

6. C++

7. """"""""""
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8. """"""""""
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9. ##########
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10. + iOS 7

12. The time you would spend on a
rewrite could instead be spent on
building cool features foryour users.

13. I ❤

14. [Obj-C]

15. Objective - ?

16. TOTHE MACRO-MOBILE!

17. #define OPTIONAL(variable)
#define IF_LET(variable, block)
#define GUARD_LET(variable, block)

18. #define OPTIONAL(variable)
#define IF_LET(variable, block)
#define GUARD_LET(variable, block)

19. 5 ways you can make your
Objective-C code better * ,
while still being Objective-C.

20. 5 ways you can make your
Objective-C code better * ,
while still being Objective-C.
*Predictable, readable, compile-time checked

21. 1. Nullability

22. Having stricter rules about
nullability reduces errors
with unexpected nil values.

23. Setting *)loadSettingWithIdentifier:(NSString *)identifier;
/**
* Load a setting with a given identifier
*
* @param identifier The identifier of the setting. Must not be nil!
*
* @return A setting object
*
* @warning May return nil!
*/
- (

24. Setting *)loadSettingWithIdentifier:(NSString *)identifier;
/**
* Load a setting with a given identifier
*
* @param identifier The identifier of the setting. Must not be nil!
*
* @return A setting object
*
* @warning May return nil!
*/
- (

25. /**
* Load a setting with a given identifier
*
* @param identifier The identifier of the setting. Must not be nil!
*
* @return A setting object
*
* @warning May return nil!
*/
- ( Setting *)loadSettingWithIdentifier:(NSString *)identifier;nullable

26. /**
* Load a setting with a given identifier
*
* @param identifier The identifier of the setting. Must not be nil!
*
* @return A setting object
*
* @warning May return nil!
*/
- ( Setting *)loadSettingWithIdentifier:(NSString *)identifier;nullable
NS_ASSUME_NONNULL_BEGIN

27. /**
* Load a setting with a given identifier
*
* @param identifier The identifier of the setting. Must not be nil!
*
* @return A setting object
*
* @warning May return nil!
*/
- ( Setting *)loadSettingWithIdentifier:(NSString *)identifier;nullable
NS_ASSUME_NONNULL_BEGIN
NS_ASSUME_NONNULL_END

28. /**
* Load a setting with a given identifier
*
* @param identifier The identifier of the setting
*
* @return A setting object
*/
- ( Setting *)loadSettingWithIdentifier:(NSString *)identifier;nullable
NS_ASSUME_NONNULL_BEGIN
NS_ASSUME_NONNULL_END

29. /**
* Load a setting with a given identifier
*
* @param identifier The identifier of the setting
*
* @return A setting object
*/
- ( Setting *)loadSettingWithIdentifier:(NSString *)identifier;nullable
NS_ASSUME_NONNULL_BEGIN
NS_ASSUME_NONNULL_END Cleaner, self-documenting interface $

30. [settingsLoader loadSettingWithIdentifier:nil];

31. - (BOOL)isSettingEnabledForIdentifier:(nullable NSString *)identifier
{
return [self loadSettingWithIdentifier:identifier].isEnabled;
}

32. - (BOOL)isSettingEnabledForIdentifier:(nullable NSString *)identifier
{
return [self loadSettingWithIdentifier:identifier].isEnabled;
}
No compilerwarning %

33. - (BOOL)isSettingEnabledForIdentifier:(nullable NSString *)identifier
{
return [self loadSettingWithIdentifier:identifier].isEnabled;
}
No compilerwarning %
Incorrect Uses Of NullableValues:YES

34. - (BOOL)isSettingEnabledForIdentifier:(nullable NSString *)identifier
{
return [self loadSettingWithIdentifier:identifier].isEnabled;
}
Incorrect Uses Of NullableValues:YES

35. - (BOOL)isShuffleSettingEnabled
{
NSString *identifier = nil;
return [self loadSettingWithIdentifier:identifier].isEnabled;
}

36. - (BOOL)isShuffleSettingEnabled
{
NSString *identifier = nil;
return [self loadSettingWithIdentifier:identifier].isEnabled;
}
No compilerwarning %

37. - (BOOL)isShuffleSettingEnabled
{
NSString *identifier = nil;
return [self loadSettingWithIdentifier:identifier].isEnabled;
}
No compilerwarning %
StaticAnalyzerto the rescue!

38. - (BOOL)isShuffleSettingEnabled
{
NSString *identifier = nil;
return [self loadSettingWithIdentifier:identifier].isEnabled;
}
StaticAnalyzerto the rescue!

39. 2. Constants

40. Constants are great, because
they increase predictability of
our code, and reduce state.

41. let string = "Hello"

42. let string = "Hello"
string = "World"

43. let string = "Hello"
string = "World"

44. let string = "Hello"
string = "World"
NSString * const string = @"Hello";

45. let string = "Hello"
string = "World"
NSString * const string = @"Hello";
string = @"World";

46. let string = "Hello"
string = "World"
NSString * const string = @"Hello";
string = @"World";

47. class Model {
let identifier: NSUUID
}

48. class Model {
let identifier: NSUUID
}
@interface Model : NSObject
@property (nonatomic, strong, readonly) NSUUID *identifier;
@end

49. class Model {
let identifier: NSUUID
}
@interface Model : NSObject
@property (nonatomic, strong, readonly) NSUUID *identifier;
@end
self.identifier = [NSUUID UUID];

50. class Model {
let identifier: NSUUID
}
@interface Model : NSObject
@property (nonatomic, strong, readonly) NSUUID *identifier;
@end
self.identifier = [NSUUID UUID];

51. 3. Designated initializers

52. @interface DataLoader : NSObject
- (instancetype)initWithNetworkController:(NetworkController *)networkController;
@end

53. NS_DESIGNATED_INITIALIZER
@interface DataLoader : NSObject
- (instancetype)initWithNetworkController:(NetworkController *)networkController ;
@end

54. NS_DESIGNATED_INITIALIZER
@interface DataLoader : NSObject
- (instancetype)initWithNetworkController:(NetworkController *)networkController ;
DataLoader * const dataLoader = [[DataLoader alloc] init];
@end

55. NS_DESIGNATED_INITIALIZER
@interface DataLoader : NSObject
- (instancetype)initWithNetworkController:(NetworkController *)networkController ;
DataLoader * const dataLoader = [[DataLoader alloc] init];
@end
No compilerwarning %

56. NS_DESIGNATED_INITIALIZER
@interface DataLoader : NSObject
- (instancetype)initWithNetworkController:(NetworkController *)networkController ;
@end
+ (instancetype)new NS_UNAVAILABLE;
- (instancetype)init NS_UNAVAILABLE;
DataLoader * const dataLoader = [[DataLoader alloc] init];
No compilerwarning %

57. NS_DESIGNATED_INITIALIZER
@interface DataLoader : NSObject
- (instancetype)initWithNetworkController:(NetworkController *)networkController ;
@end
+ (instancetype)new NS_UNAVAILABLE;
- (instancetype)init NS_UNAVAILABLE;
DataLoader * const dataLoader = [[DataLoader alloc] init];

58. By enforcing the use of a
designated (or convenience)
initializer, we can make sure our
objects are set up correctly.

59. 4. Manage weak references

60. @interface AnimationController : NSObject
@property (nonatomic, weak, nullable) id<AnimationDelegate> delegate;
- (void)performAnimation:(Animation *)animation;
@end

61. @interface AnimationController : NSObject
@property (nonatomic, weak, nullable) id<AnimationDelegate> delegate;
- (void)performAnimation:(Animation *)animation;
@end
@protocol AnimationDelegate <NSObject>
- (void)animationController:(AnimationController *)controller
animationDidBegin:(Animation *)animation;
- (void)animationController:(AnimationController *)controller
animationDidEnd:(Animation *)animation;
- (BOOL)animationController:(AnimationController *)controller
shouldRepeatAnimation:(Animation *)animation;
@end

62. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end

63. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end

64. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end

65. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end

66. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end
Delegate may be released

67. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end No compilerwarning %
Delegate may be released

68. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end No compilerwarning %
Repeatedly using a __weak reference:YES
Delegate may be released

69. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
[self.delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [self.delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[self.delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end
Repeatedly using a __weak reference:YES
Delegate may be released

70. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
id<AnimationDelegate> const delegate = self.delegate;
[delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end

71. @implementation AnimationController
- (void)performAnimation:(Animation *)animation
{
id<AnimationDelegate> const delegate = self.delegate;
[delegate animationController:self
animationDidBegin:animation];
[animation playWithCompletionHandler:^{
BOOL const shouldRepeat = [delegate animationController:self
shouldRepeatAnimation:animation];
if (shouldRepeat) {
[self performAnimation:animation];
} else {
[delegate animationController:self
animationDidEnd:animation];
}
}];
}
@end
Predictable delegate behavior $

72. When references are released
unexpectedly, it can put our
app in an undefined state.

73. 5. Strong typing

74. id

75. id
NSString
NSURL
UIView
UIColor

76. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
* const array = @[color];

77. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
Runtime crash &
* const array = @[color];

78. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
Runtime crash &
* const array = @[color];

79. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
Runtime crash &
* const array = @[color];

80. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
Runtime crash &
Generic annotations to the rescue!
* const array = @[color];

81. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
Runtime crash &
Generic annotations to the rescue!
* const array = @[color];<UIColor *>

82. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
Runtime crash &
Generic annotations to the rescue!
* const array = @[color];<UIColor *>

83. id
NSString
NSURL
UIView
UIColor
NSString * const string = @“Hello";
UIColor * const color = [UIColor redColor];
NSArray
NSString * const combinedString = [string stringByAppendingString:array[0]];
Generic annotations to the rescue!
* const array = @[color];<UIColor *>

84. NSArray<ObjectType>
NSDictionary<KeyType, ObjectType>
NSSet<ObjectType>

85. NSArray<ObjectType>
NSDictionary<KeyType, ObjectType>
NSSet<ObjectType>
@interface Collection<__covariant ObjectType> : NSObject
- (void)addObject:(ObjectType)object;
@end

86. By retaining type information
throughout our code, we can
make our code more predictable.

87. Demo

88. 1. Nullability
2. Constants
3. Designated initializers
4. Manage weak references
5. Strong typing

89. @johnsundell
josu@spotify.com
github.com/johnsundell