## Subscripts ~~~ subscript(index: Int) -> Int { get { // return an appropriate subscript value here } set(newValue) { // perform a suitable setting action here } } // read-only subscript subscript(index: Int) -> Int { // return an appropriate subscript value here } struct TimesTable { let multiplier: Int subscript(index: Int) -> Int { return multiplier * index } } let threeTimesTable = TimesTable(multiplier: 3) println("six times three is \(threeTimesTable[6])") // prints "six times three is 18" ~~~ ~~~ struct Matrix { let rows: Int, columns: Int var grid: Double[] init(rows: Int, columns: Int) { self.rows = rows self.columns = columns grid = Array(count: rows * columns, repeatedValue: 0.0) } func indexIsValidForRow(row: Int, column: Int) -> Bool { return row >= 0 && row < rows && column >= 0 && column < columns } subscript(row: Int, column: Int) -> Double { get { assert(indexIsValidForRow(row, column: column), "Index out of range") return grid[(row * columns) + column] } set { assert(indexIsValidForRow(row, column: column), "Index out of range") grid[(row * columns) + column] = newValue } } } var matrix = Matrix(rows: 2, columns: 2) matrix[0, 1] = 1.5 matrix[1, 0] = 3.2 let someValue = matrix[2, 2] // this triggers an assert, because [2, 2] is outside of the matrix bounds ~~~