SWIFT - TYPE CASTING

Transcription

1 SWIFT - TYPE CASTING Copyright tutorialspoint.com To validate the type of an instance 'Type Casting' comes into play in Swift language. It is used to check whether the instance type belongs to a particular super class or subclass or it is defined in its own hierarchy. Swift type casting provides two operators 'is' to check the type of a value and 'as' and to cast the type value to a different type. Type casting also checks whether the instance type follows particular protocol conformance standard. Defining a Class Hierarchy Type casting is used to check the type of instances either it belongs to particular class type. Also, it checks hierarchy of classes and its subclasses to check and cast those instances to make it as a same hierarchy. Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")] Type Checking Type checking is done with the 'is' operator. The 'is' type check operator checks whether the

2 instance belongs to particular subclass type and returns 'true' if it belongs to that instance else it will return 'false'. var mathscount = 0 for item in sa { if item is Chemistry { ++chemcount else if item is Maths { ++mathscount println("subjects in chemistry contains \(chemcount) topics and maths contains \(mathscount) topics") Subjects in chemistry contains 2 topics and maths contains 3 topics Downcasting Downcasting the subclass type can be done with two operators as?andas!.'as?' returns an optional

3 value when the value returns nil. It is used to check successful downcast. 'as!' returns force unwrapping as discussed in the optional chaining when the downcasting returns nil value. It is used to trigger runtime error in case of downcast failure var mathscount = 0 for item in sa { if let print = item as? Chemistry { println("chemistry topics are: '\(print.physics)', \(print.equations)") else if let example = item as? Maths { println("maths topics are: '\(example.physics)', \(example.formulae)") Chemistry topics are: 'solid physics', Hertz Maths topics are: 'Fluid Dynamics', Giga Hertz Chemistry topics are: 'Thermo physics', Decibels Maths topics are: 'Astro Physics', MegaHertz Maths topics are: 'Differential Equations', Cosine Series

4 Typecasting:Any and Any Object To represent instance which belongs to any type including function types 'Any' keyword is used var mathscount = 0 for item in sa { if let print = item as? Chemistry { println("chemistry topics are: '\(print.physics)', \(print.equations)") else if let example = item as? Maths { println("maths topics are: '\(example.physics)', \(example.formulae)") var exampleany = [Any]() exampleany.append(12) exampleany.append( ) exampleany.append("example for Any") exampleany.append(chemistry(physics: "solid physics", equations: "Hertz")) for print in exampleany { switch print { case let someint as Int: println("integer value is \(someint)") case let somedouble as Double where somedouble > 0: println("pi value is \(somedouble)") case let somestring as String:

5 println("\(somestring)") case let phy as Chemistry: println("topics '\(phy.physics)', \(phy.equations)") default: println("none") Chemistry topics are: 'solid physics', Hertz Maths topics are: 'Fluid Dynamics', Giga Hertz Chemistry topics are: 'Thermo physics', Decibels Maths topics are: 'Astro Physics', MegaHertz Maths topics are: 'Differential Equations', Cosine Series Integer value is 12 Pi value is Example for Any Topics 'solid physics', Hertz AnyObject To represent instance of any class type 'AnyObject' keyword is used let saprint: [AnyObject] = [

6 var mathscount = 0 for item in saprint { if let print = item as? Chemistry { println("chemistry topics are: '\(print.physics)', \(print.equations)") else if let example = item as? Maths { println("maths topics are: '\(example.physics)', \(example.formulae)") var exampleany = [Any]() exampleany.append(12) exampleany.append( ) exampleany.append("example for Any") exampleany.append(chemistry(physics: "solid physics", equations: "Hertz")) for print in exampleany { switch print { case let someint as Int: println("integer value is \(someint)") case let somedouble as Double where somedouble > 0: println("pi value is \(somedouble)") case let somestring as String: println("\(somestring)") case let phy as Chemistry: println("topics '\(phy.physics)', \(phy.equations)") default: println("none") Chemistry topics are: 'solid physics', Hertz Maths topics are: 'Fluid Dynamics', Giga Hertz Chemistry topics are: 'Thermo physics', Decibels Maths topics are: 'Astro Physics', MegaHertz Maths topics are: 'Differential Equations', Cosine Series Integer value is 12 Pi value is Example for Any Topics 'solid physics', Hertz Loading [MathJax]/jax/output/HTML-CSS/jax.js