subscript implementation

// subscript implementation
struct multiple{
    var num: Int = 1
    subscript(index: Int) -> Int{
        return index * num
    }
}
var newTable = multiple(num: 3)
print("3 six times is: \(newTable[6]) ")


// subscript options
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 isIndexValid(row: Int, column: Int) -> Bool{
        return rows >= 0 && row < rows && columns >= 0 && column < columns
    }
    
    subscript(row: Int, column: Int) -> Double {
        get{
            assert(isIndexValid(row: row, column: column), "the index is out of range")
            return grid[(row * column) + column]
        }
        set{
            assert(isIndexValid(row: row, column: column), "the index is out of range")
            grid[(row * column) + column] = newValue
        }
    }
}
var matrix = Matrix(rows: 2, columns: 3)
matrix[0,1] = 1.5
matrix[1,0] = 1.3

// An assertion is triggered if you try to access a subscript that’s outside of the matrix bounds:
// let someMatrix = matrix[2,2]