Swift - Subscripts

• 输入参数能够为任意类型，Subscripts 能够返回任意类型
• 能够使用多变参数，但是不能使用输入输出参数和默认参数值
• 一个类和结构体能够提供许多下标实现
• 定义多个 Subcripts 被称为 Subscripts overloading

// 和计算属性用法相似
subscript(index: Int) -> Int {
     get {
     }
     set(newValue) {
     }
}

Usage

struct TimesTable {
    let multiplier: Int
    subscript(index: Int) -> Int {
        return multiplier * index
    }
}
let threeTimesTable = TimesTable(multiplier: 3)
print("six times three is \(threeTimesTable[6])")

Dictionary

var numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
numberOfLegs["bird"] = 2
numberOfLegs["spider"] = nil // 移除 key
numberOfLegs["bird"] // return Optional

Multiple Parameter

struct Martix {
    let rows: Int, columns: Int
    var grid: [Double]
    init(rows: Int, columns: Int) {
        self.rows = rows
        self.columns = columns
        grid = Array(repeating: 0.0, count: rows * columns)
    }
  
    func indexIsVaild(row: Int, column: Int) -> Bool {
        return row >= 0 && row < rows && rolumn >= 0 && column < columns
    }

    subscript(row: Int, column: Int) -> Double {
        get {
            assert(indexIsVaild(row: row, colum: colum), "Index out of range")
            return grid[(row * columns) + column]
        }
        set {
            assert(indexIsVaild(row: row, column: column), "Index out of range")
            grid[(row * columns) + column] = newValue
        }
    }
}