Swift Language Guide - Methods

Instance Methods

Instance Methods are functions in Class(class), Structure(struct) and Enumerations(enum).

• The first parameter in method is a local parameter name by default.
• The Second and Subsequence parameters are local and External names by default.
• Use _ before parameter to disable External name

• self is like this in Java

    class Point : Printable {
  
        var x = 0, y = 0
  
        init(x: Int, y: Int) {
            self.x = x
            self.y = y
        }
  
        var description : String {
            return "(\(x), \(y))"
        }
  
        func moveToX(x: Int, andY: Int) {   <-- andY is an external name
            self.x = x
            self.y = andY
        }
  
        func moveTo(x: Int, _ y: Int) { <-- use _ to disable external name
            self.x = x
            self.y = y
        }
    }
  
  
    let point = Point(x: 10, y: 20)
    println(point)
    point.moveToX(30, andY: 40)     <-- invoke with external name
    println(point)
    point.moveTo(50, 60)
    println(point)
  

Instance Methods in Structure and Enumerations

Structure(struct) and Enumerations(enum) are Value Type.

• Functions MUST have mutating when modifying properties.

• Can NOT invoking a mutating function of a Constant structure or enumerations.

    struct Point : Printable {
        var x: Double = 0.0, y: Double = 0.0
  
  
        var description : String {
            return "(\(x), \(y))"
        }
  
        func getX() -> Double {
            return self.x
        }
  
        func getY() -> Double {
            return self.y
        }
  
        mutating func moveTo(x: Double, andY y: Double) {   <-- Change x and y property, so MUST have mutating.
            self.x = x
            self.y = y
        }
  
        func distance(that: Point) -> Double {
            let dx = (self.x - that.x)
            let dy = (self.y - that.y)
  
            return sqrt(dx * dx + dy * dy)
        }
  
    }
  
    var point1 = Point(x: 10, y: 10)
    var point2 = Point(x: 20, y: 20)
  
    println("point1 = \(point1)")
    println("point2 = \(point2)")
  
    point1.moveTo(10, andY: 20)
  
    println("point1 = \(point1)")
    println("point1.X = \(point1.x)")
    println("point1.Y = \(point1.y)")
    println("Distance between point1 and point2 is \(point1.distance(point2))")
  
  
    let origin = Point(x: 0.0, y: 0.0)      <-- Constant structure
    println("origin = \(origin)")
    println("Distance between point and origin is \(origin.distance(point1))")
  
    origin.moveTo(30, andY: 40)     <-- Error. Can NOT invoke a mutating function of Constant structure.