Objec&ve(Superman

$ whoami

iOS$Champion$@$wondermall.com

Looks%familiar?

// NSMutableDictionary *counters, id key

if (!counters[key]) { counters[key] = @1;} else { NSUInteger i = [counters[key] integerValue]; counters[key] = @(i + 1);}

NSInteger count = [counters[key] integerValue];

We#can#do#be*er!

// NSCountedSet *counters, id key

[counters addObject:key];

NSUInteger count = [counters countForObject:key];

When%the%scheiße%hits%the%fan

• How%o&en%did%you%use%NSCountedSet?

• Know%what%is%there%at%your%disposal.

• !%hits%the%fan%=%"

Swizzling

The$way$to$swizzle

As#done#by#those#fine#gentleman:

• Mike&Ash:&"Method&Replacement&for&Fun&and&Profit"1

• Jonathan&"Wolf"&Rentzsch:&JRSwizzle2

2"h$ps://github.com/rentzsch/jrswizzle

1"h$ps://www.mikeash.com/pyblog/friday9qa920109019299method9replacement9for9fun9and9profit.html

The$way$to$swizzle@implementation UIViewController (EveryDayImSwizzling)

+ (void)load { [UIViewController jr_swizzleMethod:@selector(viewDidLoad) withMethod:@selector(xyz_viewDidLoad) error:nil];}

- (void)xyz_viewDidLoad { NSLog(@"I was here"); [self xyz_viewDidLoad];}

- (void)viewDidLoad {

NSLog(@"!");}

@end

The$right$way$to$swizzle3

• Each&method&has&implicit&id&&&_cmd

• Read&about&other&people&suffering4

4"h$p://petersteinberger.com/blog/2014/a9story9about9swizzling9the9right9way9and9touch9forwarding

3"h$p://blog.newrelic.com/2014/04/16/right:way:to:swizzle/

Demo%!

Swizzling()ps

• Prefix:(xyz_

• Calling(original(method:([self xyz_swizzleMe]

• If(swizzling(ini9alisers,(hint(ARC(seman9cs(by(adding(__attribute__((objc_method_family(init)))5

• The(right(way(to(swizzle:(func9ons(or(blocks,(remember(_cmd.

5"h$p://clang.llvm.org/docs/A$ributeReference.html#objc>method>family

Proper&es(inspec&on6

6"Ivars,"too."Remember"ivars?

Proper&es(introspec&on:(cool(stuff.

• List&all&the&proper.es:&name&/&type.

• Type,&even&if&nil&or&incorrect&type.

• Accessors&(readonly,&copy,&getter=isHidden…).

• Applica.ons:&automa.c&parsing,&valida.on,&IOC7&etc.

7"h$ps://github.com/tomersh/AppleGuice

Proper&es(introspec&on:(Mantle8

• Reduces(amount(of(boilerplate

• Serialize(to(JSON,(CoreData,(XML(!

• Deserialize(dates,(enums,(URLs(etc.

• ValidaBon.

• NSCopying(and(NSCoding.

8"h$ps://github.com/Mantle/Mantle

Demo%!

Proper&es(introspec&on(&ps

• Does&not&include&proper0es&from&superclasses,&while5loop&that&class&chain!

• Automa0c&parsing&is&dangerous&(just&like&self5driving&cars).

• Assigning&through&KVC,&always&check&for&readonly.

• Did&you&call&me&lazy?

Dynamic(class(crea-on

Dynamic(class(crea-on

• Just&like&a&regular&subclassing.

• Leave&no&trace:&class&does&not&exist&in&assembly.

• Dynamically&assemble&class&on&the&fly.

• Simulate&mul>ple&inheritance.

Demo%!

Dynamic(class(crea-on:(-ps

• UIKit'&'Founda/on'use'it'twice.'Twice!

• Seems'like'a'very'esoteric'exercise.

• You'want'to'know'it's'there'when'you'need'it.

• When'do'you'need'it?

Let's&build&KVO

Let's&build&KVO

• We$want$to$know$when$any$given$property$is$set

• What$a$coincidence,$we$just$learned$everything$we$need!

• Create$a$custom$subclass.

• Swizzle$se@er$for$specified$property.

• Set$our$subclass$as$observed$object$class.

Demo%!

Let's&build&KVO

• Curiosity

• KVO-for-ge1er

• KVO-for-collec4ons

• Inject-side-effects-into-se1ers-and-ge1ers-of-all-subclasses-of-a-certain-class,-e.g.-createdAt,-updatedAt,-lastAccessedAt

Conclusion

• <objc/runtime.h>"!="App"Store.

• I"say,"test"it,"Mantle"is"a"produc7on"

grade"code.

• Swizzling"to"patch"UIKit"gotchas!9

• Objec7veDC"run7me"is"its"own"

kryptonite.

• "Wax"on,"wax"off""–"it"comes"together,"

when"you"need"it.

9"h$p://petersteinberger.com

One$more$thing...

Unicode(2015:(Diversity

S"ll$no$black$cat$emoji$!

Thank&you• This&talk&and&demos&github.com/zats/Presenta9ons

• Objec9ve=C&run9me&opensource.apple.com

• twiAer.com/zats

• github.com/zats

• 9nder.com/zats