The document discusses different approaches for designing APIs in iOS development. It begins by examining a subclass approach that limits flexibility but is simple to use. It then explores using a category/extension which allows the API to work on any class but cannot add properties. The document dives into implementing properties by associating objects at runtime, but notes this leads to a lot of boilerplate code that does not scale well. Overall, the document evaluates tradeoffs between approaches for building APIs.

1. iOSAPIDesign

2. what’sthecoolestthingabout
iOSdevelopment?
- I’m sure everyone has a different opinion on this

3. - Able to make delightful user interfaces
- This is JVFloatLabeledTextField
- Engrossing interfaces are at the core of the iPhone

4. - Able to make delightful user interfaces
- This is JVFloatLabeledTextField
- Engrossing interfaces are at the core of the iPhone

5. sharingiscaring
- With dependency managers like Carthage and CocoaPods, it’s easy to create and share your designs

6. showyoucarewithyourAPI
- But just sharing your design isn’t enough
- You have to make it easy for people to use it
- But this reminds me of a great quote from Kent Beck…

7. “🙅”
-KentBeck
- Everything is a tradeoff. (paraphrasing here)
- What makes a good API? There are very few clear answers, instead we have to evaluate tradeoffs

8. - What’s the API for JVFloatLabeledTextField?

9. - What’s the API for JVFloatLabeledTextField?

10. @interface JVFloatLabeledTextField : UITextField
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
- Really nice, allows you to use UIAppearance

11. @interface JVFloatLabeledTextField : UITextField
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
- Really nice, allows you to use UIAppearance

12. CGRect frame = CGRectMake(0.f, 0.f, 100.f, 44.f);
JVFloatLabeledTextField *textField =
[[JVFloatLabeledTextField alloc] initWithFrame:frame];
textField.placeholder = @"Price";
textField.floatingLabelYPadding = 10.f;
textField.floatingLabelTextColor = [UIColor blueColor];
- Pretty simple to use
- But it’s a specific class

13. CGRect frame = CGRectMake(0.f, 0.f, 100.f, 44.f);
JVFloatLabeledTextField *textField =
[[JVFloatLabeledTextField alloc] initWithFrame:frame];
textField.placeholder = @"Price";
textField.floatingLabelYPadding = 10.f;
textField.floatingLabelTextColor = [UIColor blueColor];
- Pretty simple to use
- But it’s a specific class

14. CGRect frame = CGRectMake(0.f, 0.f, 100.f, 44.f);
JVFloatLabeledTextField *textField =
[[JVFloatLabeledTextField alloc] initWithFrame:frame];
textField.placeholder = @"Price";
textField.floatingLabelYPadding = 10.f;
textField.floatingLabelTextColor = [UIColor blueColor];
- Pretty simple to use
- But it’s a specific class

15. subclassesforcepeopleto
useyourclassexclusively
- This is limiting

16. - MHTextField provides a next/previous input accessory view and scrolling, but is also a subclass
- Subclasses force us to choose one over the other

17. - MHTextField provides a next/previous input accessory view and scrolling, but is also a subclass
- Subclasses force us to choose one over the other

18. @interface UITextField (JVFloatLabeledTextField)
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
@interface JVFloatLabeledTextField : UITextField
- A category in ObjC, or an extension in Swift, allows people to use the implementation with *any* text field
- But we can’t add properties on categories/extensions

19. @interface UITextField (JVFloatLabeledTextField)
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
- A category in ObjC, or an extension in Swift, allows people to use the implementation with *any* text field
- But we can’t add properties on categories/extensions

20. @interface UITextField (JVFloatLabeledTextField)
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
- A category in ObjC, or an extension in Swift, allows people to use the implementation with *any* text field
- But we can’t add properties on categories/extensions

21. @interface UITextField (JVFloatLabeledTextField) {
CGFloat _floatingLabelYPadding;
}
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@end
- More precisely, defining a property automatically synthesizes an instance variable
- Can’t do that on a category/extension

22. @interface UITextField (JVFloatLabeledTextField) {
CGFloat _floatingLabelYPadding;
}
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@end
- More precisely, defining a property automatically synthesizes an instance variable
- Can’t do that on a category/extension

23. const void * const YPaddingKey = &YPaddingKey;
- (void)setFloatingLabelYPadding:(CGFloat)yPadding {
objc_setAssociatedObject(
self,
YPaddingKey,
@(yPadding),
OBJC_ASSOCIATION_RETAIN_NONATOMIC
);
}
- (CGFloat)floatingLabelYPadding {
return [objc_getAssociatedObject(self, YPaddingKey)
floatValue];
}
- An ivar won’t be auto synthesized if you define custom setters and getters
- We can dynamically tack on objects using the runtime

24. const void * const YPaddingKey = &YPaddingKey;
- (void)setFloatingLabelYPadding:(CGFloat)yPadding {
objc_setAssociatedObject(
self,
YPaddingKey,
@(yPadding),
OBJC_ASSOCIATION_RETAIN_NONATOMIC
);
}
- (CGFloat)floatingLabelYPadding {
return [objc_getAssociatedObject(self, YPaddingKey)
floatValue];
}
- An ivar won’t be auto synthesized if you define custom setters and getters
- We can dynamically tack on objects using the runtime

25. const void * const YPaddingKey = &YPaddingKey;
- (void)setFloatingLabelYPadding:(CGFloat)yPadding {
objc_setAssociatedObject(
self,
YPaddingKey,
@(yPadding),
OBJC_ASSOCIATION_RETAIN_NONATOMIC
);
}
- (CGFloat)floatingLabelYPadding {
return [objc_getAssociatedObject(self, YPaddingKey)
floatValue];
}
- An ivar won’t be auto synthesized if you define custom setters and getters
- We can dynamically tack on objects using the runtime

26. @interface UITextField (JVFloatLabeledTextField)
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
- So we just do the same for every property, right?

27. @interface UITextField (JVFloatLabeledTextField)
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
- So we just do the same for every property, right?

28. const void * const YPaddingKey = &YPaddingKey;
const void * const FontKey = &FontKey;
const void * const TextColorKey = &TextColorKey;
- (void)setFloatingLabelYPadding:(CGFloat)yPadding {
objc_setAssociatedObject(
self,
YPaddingKey,
@(yPadding),
OBJC_ASSOCIATION_RETAIN_NONATOMIC
);
}
- (CGFloat)floatingLabelYPadding {
return [objc_getAssociatedObject(self, YPaddingKey)
floatValue];
}
- Results in a ton of code for only 3 properties

29. }
- (UIFont *)floatingLabelFont {
return objc_getAssociatedObject(self, FontKey);
}
- (void)setFloatingLabelTextColor:(UIColor *)color {
objc_setAssociatedObject(
self,
TextColorKey,
color,
OBJC_ASSOCIATION_RETAIN_NONATOMIC
);
}
- (UIColor *)floatingLabelTextColor {
return objc_getAssociatedObject(self, TextColorKey);
}
- Results in a ton of code for only 3 properties

30. extension UITextField {
var floatingLabelYPadding: CGFloat {
set {
objc_setAssociatedObject(
self,
YPaddingKey,
newValue,
UInt(OBJC_ASSOCIATION_ASSIGN)
)
}
get {
if let padding = objc_getAssociatedObject(
self, YPaddingKey) as? CGFloat {
return padding
} else {
return 0
}
- In Swift, it’s worse—notice we have to be explicit about the fact that the assoc object might not be set, or may not be the
right type.
- And so much code!

31. extension UITextField {
var floatingLabelYPadding: CGFloat {
set {
objc_setAssociatedObject(
self,
YPaddingKey,
newValue,
UInt(OBJC_ASSOCIATION_ASSIGN)
)
}
get {
if let padding = objc_getAssociatedObject(
self, YPaddingKey) as? CGFloat {
return padding
} else {
return 0
}
- In Swift, it’s worse—notice we have to be explicit about the fact that the assoc object might not be set, or may not be the
right type.
- And so much code!

32. set {
objc_setAssociatedObject(
self,
TextColorKey,
newValue,
UInt(OBJC_ASSOCIATION_RETAIN_NONATOMIC)
)
}
get {
if let color = objc_getAssociatedObject(
self, TextColorKey) as? UIColor {
return color
} else {
return UIColor.blackColor()
}
}
}
}
- In Swift, it’s worse—notice we have to be explicit about the fact that the assoc object might not be set, or may not be the
right type.
- And so much code!

33. doesn’tscale
- Defining two methods for every new property is nuts
- Too much boilerplate code, but also…

34. // objc4-532/runtime/objc-references.mm
// class AssociationsManager manages a lock / hash table
// singleton pair. Allocating an instance acquires the
// lock, and calling its assocations() method
// lazily allocates it.
class AssociationsManager {
static OSSpinLock _lock;
// associative references:
// object pointer -> PtrPtrHashMap.
static AssociationsHashMap *_map;
public:
AssociationsManager() { OSSpinLockLock(&_lock); }
~AssociationsManager() { OSSpinLockUnlock(&_lock); }
};
- Associated objects are stored in a global hashmap
- The more you add, the worse performance/memory usage gets
- Of course, reference counting also works this way, but…

35. CGFloat *floatingLabelYPadding
UIFont *floatingLabelFont
UIColor *floatingLabelTextColor
UIColor *floatingLabelActiveColor
BOOL animateEvenIfNotFirstResponder
UITextField
(JVFloatLabeledTextField)
- Instead, we can encapsulate these properties in a single “options”, or “configuration” object

36. CGFloat *floatingLabelYPadding
UIFont *floatingLabelFont
UIColor *floatingLabelTextColor
UIColor *floatingLabelActiveColor
BOOL animateEvenIfNotFirstResponder
JVFloatLabeledOptions
- Instead, we can encapsulate these properties in a single “options”, or “configuration” object

37. CGFloat *floatingLabelYPadding
UIFont *floatingLabelFont
UIColor *floatingLabelTextColor
UIColor *floatingLabelActiveColor
BOOL animateEvenIfNotFirstResponder
JVFloatLabeledOptions
UITextField
(JVFloatLabeledTextField)
JVFloatLabeledOptions *options
- Instead, we can encapsulate these properties in a single “options”, or “configuration” object

38. @interface UITextField (JVFloatLabeledTextField)
@property (nonatomic, copy)
JVFloatLabeledOptions *options;
@end
- Now we have just one property, options

39. @interface UITextField (JVFloatLabeledTextField)
@property (nonatomic, copy)
JVFloatLabeledOptions *options;
@end
- Now we have just one property, options

40. @interface JVFloatLabeledOptions : NSObject
@property (nonatomic, assign)
CGFloat floatingLabelYPadding UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIFont *floatingLabelFont UI_APPEARANCE_SELECTOR;
@property (nonatomic, strong)
UIColor *floatingLabelTextColor UI_APPEARANCE_SELECTOR;
@end
- From within the implementation, we can access properties on this object
- They’re ordinary properties—no runtime

41. 🙅
- So what are the tradeoffs of using categories over subclasses?

42. composemultiplecategories
- You don’t have to choose between one set of functionality or another
- You don’t have to choose floating labels *or* a cool input accessory—you can have both

43. runtimesorcery
- Runtime manipulation makes this approach a little less safe, a little less performant

44. - I used this and other patterns in an open-source UI library I developed last year, MDCSwipeToChoose
- Category on UIView

45. - I used this and other patterns in an open-source UI library I developed last year, MDCSwipeToChoose
- Category on UIView

46. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Add swiping behavior to any view—here a web view
- We create the options object and set its properties
- Then we setup the view using the options—this can only be done once, so the properties can’t be changed—a killer
feature

47. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Add swiping behavior to any view—here a web view
- We create the options object and set its properties
- Then we setup the view using the options—this can only be done once, so the properties can’t be changed—a killer
feature

48. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Add swiping behavior to any view—here a web view
- We create the options object and set its properties
- Then we setup the view using the options—this can only be done once, so the properties can’t be changed—a killer
feature

49. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Add swiping behavior to any view—here a web view
- We create the options object and set its properties
- Then we setup the view using the options—this can only be done once, so the properties can’t be changed—a killer
feature

50. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Add swiping behavior to any view—here a web view
- We create the options object and set its properties
- Then we setup the view using the options—this can only be done once, so the properties can’t be changed—a killer
feature

51. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Add swiping behavior to any view—here a web view
- We create the options object and set its properties
- Then we setup the view using the options—this can only be done once, so the properties can’t be changed—a killer
feature

52. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Add swiping behavior to any view—here a web view
- We create the options object and set its properties
- Then we setup the view using the options—this can only be done once, so the properties can’t be changed—a killer
feature

53. - The view category is configured has a threshold—when the center of the view moves out of the threshold, it gets swiped
offscreen
- I don’t have to worry about the threshold changing, or the pan block, or anything

54. - The view category is configured has a threshold—when the center of the view moves out of the threshold, it gets swiped
offscreen
- I don’t have to worry about the threshold changing, or the pan block, or anything

55. - The view category is configured has a threshold—when the center of the view moves out of the threshold, it gets swiped
offscreen
- I don’t have to worry about the threshold changing, or the pan block, or anything

56. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Another thing to note: the pan block takes a single parameter

57. MDCSwipeOptions *options = [MDCSwipeOptions new];
options.threshold = 130.f;
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
bookmarkView.alpha = 0.f;
dontBookmarkView.alpha = state.thresholdRatio;
} else if (state.direction == MDCSwipeDirectionRight) {
bookmarkView.alpha = state.thresholdRatio;
dontBookmarkView.alpha = 0.f;
}
};
[webView mdc_swipeToChooseSetup:options];
- Another thing to note: the pan block takes a single parameter

58. // AFNetworking/AFSecurityPolicy.m
- (BOOL)evaluateServerTrust:(SecTrustRef)serverTrust {
return [self evaluateServerTrust:serverTrust
forDomain:nil];
}
// ...
- With public methods, you can define new methods, and have the old call the new with default parameters

59. // AFNetworking/AFSecurityPolicy.m
- (BOOL)evaluateServerTrust:(SecTrustRef)serverTrust {
return [self evaluateServerTrust:serverTrust
forDomain:nil];
}
- (BOOL)evaluateServerTrust:(SecTrustRef)serverTrust
forDomain:(NSString *)domain {
// ...
}
- With public methods, you can define new methods, and have the old call the new with default parameters

60. func evaluateServerTrust(
trust: SecTrustRef) -> Bool {
// ...
}
- Even easier in Swift—just define default parameters

61. func evaluateServerTrust(
trust: SecTrustRef, domain: String? = nil) -> Bool {
// ...
}
- Even easier in Swift—just define default parameters

62. options.onPan = ^(UIView *view,
MDCSwipeDirection direction) {
if (direction == MDCSwipeDirectionLeft) {
// ...panning to the left.
}
};
- Obj-C or Swift, block params and delegate callbacks lock you into an API
- So if we add a parameter here…

63. options.onPan = ^(UIView *view,
MDCSwipeDirection direction,
CGFloat thresholdRatio) {
if (direction == MDCSwipeDirectionLeft) {
// ...panning to the left.
}
};
- Obj-C or Swift, block params and delegate callbacks lock you into an API
- So if we add a parameter here…

64. view.onPan = ^(UIView *view,
MDCSwipeDirection direction) {
if (direction == MDCSwipeDirectionLeft) {
// ...
}
};
subview.onPan = ^(UIView *view,
MDCSwipeDirection direction) {
// ...
};
void (^onPanBlock)(UIView *view,
MDCSwipeDirection direction) = nil;
subview.onPan = onPanBlock;
- …every callsite breaks

65. view.onPan = ^(UIView *view,
MDCSwipeDirection direction) {
if (direction == MDCSwipeDirectionLeft) {
// ...
}
};
subview.onPan = ^(UIView *view,
MDCSwipeDirection direction) {
// ...
};
void (^onPanBlock)(UIView *view,
MDCSwipeDirection direction) = nil;
subview.onPan = onPanBlock;
- …every callsite breaks

66. options.onPan = ^(UIView *view,
MDCSwipeDirection direction,
CGFloat thresholdRatio) {
if (direction == MDCSwipeDirectionLeft) {
// ...panning to the left.
}
};
- Instead, you could encapsulate params in an object

67. options.onPan = ^(UIView *view,
MDCSwipeDirection direction,
CGFloat thresholdRatio) {
if (direction == MDCSwipeDirectionLeft) {
// ...panning to the left.
}
};
options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
- Instead, you could encapsulate params in an object

68. @interface MDCPanState : NSObject
@property (nonatomic, strong, readonly)
UIView *view;
@property (nonatomic, assign, readonly)
MDCSwipeDirection direction; DEPRECATED_ATTRIBUTE
@property (nonatomic, assign, readonly)
CGFloat thresholdRatio;
@end
- This is a design pattern that Martin Fowler calls “parameter objects”
- One benefit is that it’s easy to change
- Deprecation can help you slowly phase out APIs

69. @interface MDCPanState : NSObject
@property (nonatomic, strong, readonly)
UIView *view;
@property (nonatomic, assign, readonly)
MDCSwipeDirection direction; DEPRECATED_ATTRIBUTE
@property (nonatomic, assign, readonly)
CGFloat thresholdRatio;
@end
- This is a design pattern that Martin Fowler calls “parameter objects”
- One benefit is that it’s easy to change
- Deprecation can help you slowly phase out APIs

70. options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
// ...panning to the left.
}
};
- Users will see a warning when they attempt to use the deprecated property

71. options.onPan = ^(MDCPanState *state) {
if (state.direction == MDCSwipeDirectionLeft) {
// ...panning to the left.
}
};
- Users will see a warning when they attempt to use the deprecated property

72. @protocol MDCSwipeToChooseDelegate <NSObject>
@optional
- (void)swipeToChooseView:(UIView *)view
wasChosenWithDirection:(MDCSwipeDirection)direction;
@end
- Same goes for delegates and other protocols—changing params is a major version bump
- Use parameter object for future-proofing

73. @protocol MDCSwipeToChooseDelegate <NSObject>
@optional
- (void)swipeToChooseView:(UIView *)view
wasChosenWithDirection:(MDCSwipeDirection)direction
momentum:(CGFloat)momentum;
@end
- Same goes for delegates and other protocols—changing params is a major version bump
- Use parameter object for future-proofing

74. @protocol MDCSwipeToChooseDelegate <NSObject>
@optional
- (void)swipeToChooseView:(UIView *)view
wasChosenWithParameters:(MDCChosenParameters *)params;
@end
- Same goes for delegates and other protocols—changing params is a major version bump
- Use parameter object for future-proofing

75. 🙅
- So what are the tradeoffs of parameter objects?

76. versionyourAPI
- Future-proof block or protocol APIs

77. overhead
- Small perf overhead of creating object.
- Large dev overhead of defining new class
- Use sparingly, for public APIs that may change?

78. 1.Categoriesvs.Subclasses
- You can compose categories, with some runtime hacking

79. 2.Configurationobjects
- Configuration objects allow you to initialize an object with a set of parameters you can easily change

80. 3.Alwayspreferimmutability
- Set it and forget it—if you allow your objects to change and mutate, you’re going to be chasing subtle bugs

81. 4.Parameterobjects
- Use parameter objects to version your APIs

82. 1.Categoriesvs.Subclasses
2.Configurationobjects
3.Alwayspreferimmutability
4.Parameterobjects
Thanks!