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Diffstat (limited to 'swift.html.markdown')
| -rw-r--r-- | swift.html.markdown | 83 |
1 files changed, 51 insertions, 32 deletions
diff --git a/swift.html.markdown b/swift.html.markdown index c2fb3471..36124e11 100644 --- a/swift.html.markdown +++ b/swift.html.markdown @@ -12,7 +12,7 @@ contributors: filename: learnswift.swift --- -Swift is a programming language for iOS and OS X development created by Apple. Designed to coexist with Objective-C and to be more resilient against erroneous code, Swift was introduced in 2014 at Apple's developer conference WWDC. It is built with the LLVM compiler included in Xcode 6+. +Swift is a programming language for iOS and macOS development created by Apple. Designed to coexist with Objective-C and to be more resilient against erroneous code, Swift was introduced in 2014 at Apple's developer conference WWDC. It is built with the LLVM compiler included in Xcode 6+. The official _[Swift Programming Language](https://itunes.apple.com/us/book/swift-programming-language/id881256329)_ book from Apple is now available via iBooks. It goes into much more detail than this guide, and if you have the time and patience to read it, it's recommended. Some of these examples are from that book. @@ -91,7 +91,7 @@ let multiLineString = """ This is a multi-line string. It's called that because it takes up multiple lines (wow!) Any indentation beyond the closing quotation marks is kept, the rest is discarded. - You can include " or "" in multi-line strings because the delimeter is three "s. + You can include " or "" in multi-line strings because the delimiter is three "s. """ // Arrays @@ -159,12 +159,12 @@ let `class` = "keyword" or contains nil (no value) to indicate that a value is missing. Nil is roughly equivalent to `null` in other languages. A question mark (?) after the type marks the value as optional of that type. - + If a type is not optional, it is guaranteed to have a value. - + Because Swift requires every property to have a type, even nil must be explicitly stored as an Optional value. - + Optional<T> is an enum, with the cases .none (nil) and .some(T) (the value) */ @@ -178,7 +178,7 @@ let someOptionalString4 = String?.none //nil To access the value of an optional that has a value, use the postfix operator !, which force-unwraps it. Force-unwrapping is like saying, "I know that this optional definitely has a value, please give it to me." - + Trying to use ! to access a non-existent optional value triggers a runtime error. Always make sure that an optional contains a non-nil value before using ! to force-unwrap its value. @@ -194,7 +194,7 @@ if someOptionalString != nil { // Swift supports "optional chaining," which means that you can call functions // or get properties of optional values and they are optionals of the appropriate type. // You can even do this multiple times, hence the name "chaining." - + let empty = someOptionalString?.isEmpty // Bool? // if-let structure - @@ -334,7 +334,7 @@ repeat { } while i < 5 // The continue statement continues executing a loop at the next iteration -// The break statement ends a swift or loop immediately +// The break statement ends a loop immediately // MARK: - Functions @@ -370,7 +370,7 @@ func say(_ message: String) { } say("Hello") -// Default parameters can be ommitted when calling the function. +// Default parameters can be omitted when calling the function. func printParameters(requiredParameter r: Int, optionalParameter o: Int = 10) { print("The required parameter was \(r) and the optional parameter was \(o)") } @@ -443,7 +443,7 @@ func testGuard() { return // guard statements MUST exit the scope that they are in. // They generally use `return` or `throw`. } - + print("number is \(aNumber)") } testGuard() @@ -564,7 +564,7 @@ enum Furniture { case desk(height: Int) // Associate with String and Int case chair(String, Int) - + func description() -> String { //either placement of let is acceptable switch self { @@ -591,15 +591,15 @@ print(chair.description()) // "Chair of Foo with 40 cm" - Define initializers to set up their initial state - Be extended to expand their functionality beyond a default implementation - Conform to protocols to provide standard functionality of a certain kind - + Classes have additional capabilities that structures don't have: - Inheritance enables one class to inherit the characteristics of another. - Type casting enables you to check and interpret the type of a class instance at runtime. - Deinitializers enable an instance of a class to free up any resources it has assigned. - Reference counting allows more than one reference to a class instance. - + Unless you need to use a class for one of these reasons, use a struct. - + Structures are value types, while classes are reference types. */ @@ -607,7 +607,7 @@ print(chair.description()) // "Chair of Foo with 40 cm" struct NamesTable { let names: [String] - + // Custom subscript subscript(index: Int) -> String { return names[index] @@ -629,7 +629,7 @@ class Shape { class Rect: Shape { var sideLength: Int = 1 - + // Custom getter and setter property var perimeter: Int { get { @@ -640,38 +640,38 @@ class Rect: Shape { sideLength = newValue / 4 } } - + // Computed properties must be declared as `var`, you know, cause' they can change var smallestSideLength: Int { return self.sideLength - 1 } - + // Lazily load a property // subShape remains nil (uninitialized) until getter called lazy var subShape = Rect(sideLength: 4) - + // If you don't need a custom getter and setter, // but still want to run code before and after getting or setting // a property, you can use `willSet` and `didSet` var identifier: String = "defaultID" { - // the `willSet` arg will be the variable name for the new value + // the `someIdentifier` arg will be the variable name for the new value willSet(someIdentifier) { print(someIdentifier) } } - + init(sideLength: Int) { self.sideLength = sideLength // always super.init last when init custom properties super.init() } - + func shrink() { if sideLength > 0 { sideLength -= 1 } } - + override func getArea() -> Int { return sideLength * sideLength } @@ -679,6 +679,9 @@ class Rect: Shape { // A simple class `Square` extends `Rect` class Square: Rect { + // Use a convenience initializer to make calling a designated initializer faster and more "convenient". + // Convenience initializers call other initializers in the same class and pass default values to one or more of their parameters. + // Convenience initializers can have parameters as well, which are useful to customize the called initializer parameters or choose a proper initializer based on the value passed. convenience init() { self.init(sideLength: 5) } @@ -692,6 +695,11 @@ print(mySquare.sideLength) // 4 // cast instance let aShape = mySquare as Shape +// downcast instance: +// Because downcasting can fail, the result can be an optional (as?) or an implicitly unwrpped optional (as!). +let anOptionalSquare = aShape as? Square // This will return nil if aShape is not a Square +let aSquare = aShape as! Square // This will throw a runtime error if aShape is not a Square + // compare instances, not the same as == which compares objects (equal to) if mySquare === mySquare { print("Yep, it's mySquare") @@ -703,13 +711,13 @@ class Circle: Shape { override func getArea() -> Int { return 3 * radius * radius } - + // Place a question mark postfix after `init` is an optional init // which can return nil init?(radius: Int) { self.radius = radius super.init() - + if radius <= 0 { return nil } @@ -813,10 +821,21 @@ for _ in 0..<10 { - Internal: Accessible and subclassible in the module it is declared in. - Fileprivate: Accessible and subclassible in the file it is declared in. - Private: Accessible and subclassible in the enclosing declaration (think inner classes/structs/enums) - + See more here: https://docs.swift.org/swift-book/LanguageGuide/AccessControl.html */ +// MARK: Preventing Overrides + +// You can add keyword `final` before a class or instance method, or a property to prevent it from being overridden +class Shape { + final var finalInteger = 10 +} + +// Prevent a class from being subclassed +final class ViewManager { +} + // MARK: Conditional Compilation, Compile-Time Diagnostics, & Availability Conditions // Conditional Compilation @@ -878,11 +897,11 @@ extension Int { var doubled: Int { return self * 2 } - + func multipliedBy(num: Int) -> Int { return num * self } - + mutating func multiplyBy(num: Int) { self *= num } @@ -904,7 +923,7 @@ func findIndex<T: Equatable>(array: [T], valueToFind: T) -> Int? { } return nil } -findIndex(array: [1, 2, 3, 4], valueToFind: 3) // 2 +findIndex(array: [1, 2, 3, 4], valueToFind: 3) // Optional(2) // You can extend types with generics as well extension Array where Array.Element == Int { @@ -965,18 +984,18 @@ func fakeFetch(value: Int) throws -> String { guard 7 == value else { throw MyError.reallyBadValue(msg: "Some really bad value") } - + return "test" } func testTryStuff() { // assumes there will be no error thrown, otherwise a runtime exception is raised let _ = try! fakeFetch(value: 7) - + // if an error is thrown, then it proceeds, but if the value is nil // it also wraps every return value in an optional, even if its already optional let _ = try? fakeFetch(value: 7) - + do { // normal try operation that provides error handling via `catch` block try fakeFetch(value: 1) |