Swift

Type casting in Swift is implemented with is and as operators. Type casting: A subclass instance can be use as a superclass instance. Defining a Class Hierarchy class Media { var name: String init(name: String) { self.name = name } } class Song: Media { var artist: String init(name: String, artist: String) { self.artist = artist super.init(name: name) } } class Movie: Media { var director: String init(name: String, director: String) { self.director = director super.init(name: name) } } var library = [ Movie(name: "A", director: "Michael"), Song(name: "B", artist: "Elvis"), Movie(name: "C", director: "Orson"), Song(name: "D", artist: "Rick"), Media(name: "E") ] // The "library" is inferred to be [Media] for item in library { print(item.name) // Here the item is of "Media" type } // If we want to use the library's item as the subclass instance, we should downcast the item. Checking Type Use is to check whether an instance is of a certain subclass type. ...

Swift has built-in support for writing asynchronous and parallel code in a structured way. Parallel code means multiple pieces of code run simultaneously. Concurrency will make the code harder to debug. Swift can help to catch problem at compile time. Although it’s possible to write concurrent code without using Swift language support, that code tends to be hard to read. listPhotos(inGallery: "Summer Vacation") { photoNames in let sortedNames = photoNames.sorted() let name = sortedNames[0] downloadPhoto(named: name) { photo in show(photo) } } Keywords: ...

A class support for throwing, catching, propagating, and manipulating recoverable errors at runtime. When an optional fails, it’s useful to understand what cause the failure, so that the code can respond accordingly. Example: Reading a file from the disk may be fail in some way. File not exist Have no permission to read. File not being encoded in a compatible format. Distinguishing among these different situations allows a program to resolve some errors and to communicate to the user any errors it can’t resolve. ...

Before the object is recycle, the deinitializer solve the post events.

The class’s initializer set the original state for the object.

A class inherit another class call super class, and get some ability from super class.

The object have some method to provide functionality.

Stored properties Only provided by classed and structures. Computed properties Provide by classes, structures, enumerations. Usually associated with instance of a particular type, can be associated with the type itself(type properties). Can define property observers to monitor changes in a property’s value, which can respond to with custom action. Can use a property wrapper to reuse code in the getter and setter. Stored Properties **struct Setting { var width: Int let height: Int } var appSetting = Setting(width: 100, height: 200) appSetting.width = 150 let constSetting = Setting(width: 110, height: 210) //constSetting.width = 120 // This will trigger a compile-time error, the struct is of const value type.** Lazy Stored Properties Its initial value isn’t calculated until the first time it’s used. ...

The object oriented programming.

Syntax enum Direction { case up case down case left case right } Multiple case can appear on a single line, separated by commas: enum { case up, down, left, right } Use the Enumeration var dir = Direction.up When we want to modify the var after the initialized, we can use a shorter form of the enumeration. var dir = Direction.up dir = .down // The value's type has been inferred when the value is in initializing. Matching Enumeration Values with a Switch Statement enum Direction { case up case down case left case right } var dir = Direction.right switch dir { case .up: print("Go up") case .down: print("Go down") case .left: print("Go left") case .right: print("Go right") } Iterating over Enumeration Cases Conform to the CaseIterable protocol, to make the enumeration’s case be iterable. ...