A Swift Approach (Warsaw 2014)

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A SWIFT APPROACH KYLEFULLER

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KYLEFULLER

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NEW CONCEPTS

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RUNTIME

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@objc / NSObject

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NSKeyValueObserving

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RUNTIME

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WWDC 2015

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OPTIONALS?

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func compute() -> Bool?

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true false neither

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LACK OF A VALUE

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NOT AN EMPTY VALUE

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CAN'T WE DO THIS IN OBJECTIVE-C?

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nil Nil NULL CGRectNull -1 0 NSNotFound NSNull ...

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EXPRESS YOU DON'T ACCEPT NIL

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EXPRESS YOU WILL NOT RETURN NIL

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/// You **MUST** pass in a URL - (instancetype)initWithURL:(NSURL *)URL { NSParameterAssert(URL != nil); }

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- (UITableViewCell *)tableView:(UITableView *)tv cellForRowAtIndexPath:(NSIndexPath *)path { return nil; }

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RUNTIME ERROR

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RUNTIME ERROR

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COMPILE ERROR

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TUPLES

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func get(username:String) -> (Person?, NSError?)

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let person, error = get("Kyle")

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OBJECTIVE-C

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NSError *error; Person *person = [Person getPerson:@"Kyle" error:&error];

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NAMED TUPLES

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func get(username:String) -> (person:Person?, error:NSError?)

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let result = get("Kyle") result.person result.error

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- (NSArray *)getPerson:(NSString *)username; - (NSDictionary *)getPerson:(NSString *)username;

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NSDictionary *components = [Person getPerson:@"kyle"]; Person *person = components["person"]; NSError *error = components["error"];

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TYPE SAFETY?

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FRAGILE

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ENUMERATIONS

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enum Result { case Success(String) case Error(Error) }

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switch result { case .Error(let error): println("There was an error (\(error)).") case .Success(let string): println("\(string)") }

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CLOSURES

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EVERYTHING IS A CLOSURE

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class TestObject { func testA() -> () { println("first test") } var testB:(() -> ()) = { println("second test") } }

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let testing = TestObject() testing.testA() testing.testB()

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testing.testB = testing.testA

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testing.testB() // Actually calls testA

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CONSISTENCY

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FUNCTIONAL

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let string = "Hello World" let matches:[NSTextCheckingResult] = /* regex for words in string */ matches.map { string.substringWithRange($0.range) }

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let string = "Hello World" let matches:[NSTextCheckingResult] = /* regex for words in string */ var strings = [String]() for match in matches { let catch = string.substringWithRange(match.range) strings.append(catch) }

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func reduce(initial, combine) -> result

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combine : ((previous, current) -> (result))

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let items = [["a", "b"], ["c", "d"], ["e"]] items.reduce([]) { initial, expressions -> [String] in initial + expressions } => ["a", "b", "c", "d", "e"]

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let items = [["a", "b"], ["c", "d"], ["e"]] items.reduce([], +) => ["a", "b", "c", "d", "e"]

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func +(lhs:[T], rhs:[T]) -> [T]

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items.sort { $0 > $1 }

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items.sort(>)

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items.filter { $0.hasPermission }

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func isAdmin(user:User) -> Bool { return user.username == "Kyle" } users.filter(isAdmin)

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GENERICS

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Array

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Dictionary

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func max(a:T, b:T) -> T { return a > b ? a : b }

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max(anInteger, anotherInteger) max(aFloat, anotherFloat) max(aString, anotherString)

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PATTERN MATCHING

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let point = (1, 2) switch point { case (0, 0): println("(0, 0) is at the origin.") case (-2...2, -2...2): println("(\(point.0), \(point.1)) is near the origin.") default: println("The point is at (\(point.0), \(point.1)).") } // prints "(1, 2) is near the origin."

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@auto_closure

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delay(5, println("Hello World"))

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func delay(time:UInt32, block:@auto_closure) { sleep(time) block() }

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BUILDING ASSERT() IN SWIFT

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assert(someExpensiveComputation() != 42)

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func assert(predicate : () -> Bool) { #if !NDEBUG if !predicate() { abort() } #endif }