//: Playground - noun: a place where people can play

import UIKit

/************ 下标 ****************/
// 类, 结构体 , 枚举 可以定义下标
// 下标可以传入 多个不同类型的参数, 返回一个任意类型的数据
// 下标中 可以使用 get 和 set 模式(read-write 和 readOnly)


//subscript(index: Int) -> Int {
//    get {
//        // return an appropriate subscript value here
//        return 3
//    }
//    set(newValue) {
//        // perform a suitable setting action here
//    }
//}

//subscript(index: Int) -> Int {
//    // return an appropriate subscript value here
//    return 3
//}

struct TimesTable {
    let multiplier: Int
    subscript(index: Int) -> Int {
        return multiplier * index
    }
}
let threeTimesTable = TimesTable(multiplier: 3)
print("six times three is \(threeTimesTable[6])")
// Prints "six times three is 18”



// 在集合中使用下标
var numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
numberOfLegs["bird"] = 2


//下面有个矩阵的例子
struct Matrix{
    
    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 indexIsValid(row: Int, column: Int) -> Bool{
        return row >= 0 && row < rows && column >= 0 && column < columns
    }
    
    subscript(row: Int, column: Int) -> Double{
        
        get {
            
            assert(indexIsValid(row: row, column: column), "Index out of range")
            
            return grid[(row * column) + column]
        }
        
        set {
            
            assert(indexIsValid(row: row, column: column), "Index out of range")
            
            grid[(row * column) + column] = newValue
        }
        
    }
    
}

var matrix = Matrix(rows: 2, columns: 2)

matrix[0,1] = 1.5

matrix[1,0] = 3.2

print(matrix[0,1])
print(matrix[1,0])