enumeration

Enumeration concept

• Enumeration defines a set of related values of a common type that you can use in your code in a safe way
• Enumeration in C/OC language specifies that the related name is a set of integer values
• The enumeration in Swift is more flexible. It can provide a string, a character or an integer or floating-point value

Syntax for enumeration types

• format

enum Direction {
   case east
   case west
   case south
   case north
}
Direction.east
//perhaps
enum Direction {
   case east, west, south, north
}

• Standard
  • Enumeration type first letter lowercase

Assign to enumeration type

• In swift, enumeration type does not represent any type by default, which is an identity
• Enumeration type can be string / character / integer / floating point

   enum Direction: Int {
        case east = 2
        case west =3
        case south =4
        case north =5
   }
   //rawValue represents the original value corresponding to an enumeration
   //Enumeration value → original value
   let rv = Direction.east.rawValue
   //Original value → enumeration value
   let z Direction(rawValue : 6)
  
   //Enumerate binding strings
   enmu Path:String {
     case cache = "user/desktop/cache"
     case document = "user/desktop/doc"
   }
   func text (path:Path){
     if path == .cache {
              print(path.rawValue)
     }
    }
  

structural morphology

Basic use of structure

• Concept of structure
  • A struct is a data set composed of a series of data of the same type or different types
  • Structure refers to a data structure
  • A struct is a value type, which is passed in a method
• Structure format
  • struct structure name {property and method}
  • Both enumerations and structs can write methods
    • Type method: static func
    • Instance method: func

   struct Point {
      //Instance properties
      var x : Double
      var y : Double
      //Instance method
       func distance() {
           print("Calculate the distance between two points",x,Point.z)
   }
     //Type properties
      static var z :Double = 0
      //Type method
       static func dis() {
           print("xxx",z)
   }
   }
   Point.dis()
  

• Calculate the distance between two points

   func distance(p1:Point ,p2:Point)→Double{
    return sqrt(pow(p1.x-p2.x,2)+pow(p1.y-p2.y,2))
   }
  

Extended constructors for structs

• By default, the structure automatically creates a "one by one constructor" → the purpose is to make all "non optional" member variables have values
• Extension constructor

struct Point{
  //Non optional, never for nil
  var x :Double
  var y :Double
  var z :Double?
  //Custom constructor! = normal function
  //Without func
  //init must be used as the name
  //Inside a constructor, you must ensure that all non optional properties have values
  //If we define our own constructors now, there will be no one by one constructors automatically generated by the system
  init(x:Double,y:Double){
      self.x = x
      self.y = y
  }
  init(x:Double,y:Double,z:Double){
      self.x = x
      self.y = y
      self.z = z
  }
  
}
//When we use it directly, the "constructor" provided by the system = = "construct instance function"
//let p = Point(x:1,y:2)
//p.z = nil

let p = Point(x: 1, y: 2)
let p1 = Point(x: 1, y: 2, z: 3)

// Constructor generated by the system by default → one by one constructor
// Assign values to all the non optional attributes one by one. The purpose is to ensure that when an instance is created, all the non optional attributes have values