A process for querying and calling properties, methods, and subscripts on an optional that might currently be nil .Multiple queries can be chained together, and the chain fails gracefully if any link in the chain is nil . Optional Chaining as an Alternative to Forced Unwrapping ! force unwrapping triggers a runtime error when the optional is nil . Use the optional chaining to check if the optional value querying is succeed. the chain return optional value is nil , the optional chaining fail. the chain return optional contains a value, the optional chaining succeed. Force Unwrapping ...

A protocol defines a blueprint with methods, properties.

Extension add new functionality to an existing class, structure, enumeration, or protocol type.

Enumerations, classes or structures can be nested in another type. struct Closh { enum Size: String{ case H = "high", M = "Medium", L = "Low" } enum Detail: Int { case H = 180, M = 170, L = 160 struct Price { let normal: Int, discount: Int? } var price: Price { switch self { case .H: return Price(normal: 100, discount: 90) case .M: return Price(normal: 90, discount: 80) case .L: return Price(normal: 80, discount: 70) default: return Price(normal: self.rawValue, discount: nil) } } } let size: Size, detail: Detail var description: String { return "\(size.rawValue), PriceNormal: \(detail.price.normal) PriceDiscount: \(detail.price.discount)" } } var closh = Closh(size: .M, detail: .M) print(closh.description) // Print: Medium, PriceNormal: 90 PriceDiscount: Optional(80) Referring to Nested Types ...

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.