Subscript in swift

 

Subscript （subscript）

1、 Use subscript Any type can be given （ enumeration 、 Structure 、 class ） Add subscript function , Some places are also translated as ： Subscript script

        subscript The syntax of is similar to the instance method 、 Compute properties , Essence is method （ function ）

2、subscript The return value type defined in determines ,get Method 's return value type ,set In the method newValue The type of .

class Point {
    var x = 0.0, y = 0.0
    
    subscript(index: Int) -> Double {
        set {
            if index == 0 {
                x = newValue
            } else if index == 1 {
                y = newValue
            }
        }
        
        get {
            if index == 0 {
                return x
            } else if index == 1 {
                return y
            }
            return 0
        }
    }
}

var p = Point()
p[0] = 11.1
p[1] = 22.2
print(p.x)
print(p.y)
print(p[0])
print(p[1])

3、subscript Multiple parameters can be accepted , And of any type .

4、subscript There can be no set Method , But there must be get Method .

        If only get Method , It can be omitted get

class Point {
    var x = 0.0, y = 0.0
    
    subscript(index: Int) -> Double {
        if index == 0 {
            return x
        } else if index == 1 {
            return y
        }
        return 0
    }
}

5、 You can set parameter labels

class Point {
    var x = 0.0, y = 0.0
    
    subscript(index i: Int) -> Double {
        if i == 0 {
            return x
        } else if i == 1 {
            return y
        }
        return 0
    }
}

var p = Point()
p.y = 22.2
print(p[index: 1]) //22.2

6、 Subscripts can be type methods

class Sum {
    static subscript(v1: Int, v2: Int) -> Int {
        return v1 + v2
    }
}

print(Sum[10, 20]) //30

7、 The essence is to call the inside set and get Method

 8、 Structure 、 Class as the return value

class Point {
    var x = 10, y = 10
}

class PointManager {
    var point = Point()
    
    subscript(index: Int) -> Point {
//        set {
//            point = newValue
//        }
        
        get {
            return point
        }
    }
}

var pm = PointManager()
pm[0].x = 11
pm[0].y = 22

Point If it's a class , You don't have to write set Method ,Point If it is a structure, you must write set Method .

9、 Receive subscripts of multiple parameters

class Grid {
    var data = [
        [0, 1, 2],
        [3, 4, 5],
        [6, 7, 8]
    ]
    
    subscript(row: Int, column: Int) -> Int {
        set {
            guard row >= 0 && row < 3 && column >= 0 && column < 3 else {
                return
            }
            data[row][column] = newValue
        }
        
        get {
            guard row >= 0 && row < 3 && column >= 0 && column < 3 else {
                return 0
            }
            return data[row][column]
        }
    }
}

var grid = Grid()
grid[0, 1] = 77
grid[1, 2] = 88
grid[2, 0] = 99
print(grid.data)