A subscript is a special kind of function that allows you to access elements within a type using square bracket syntax ([]), similar to accessing array elements.
You are free to implement subscripts in the most appropriate way for your particular class or structureā€™s functionality. Types can have multiple subscripts with different parameter types.
Subscripts can take any number of input parameters, and these input parameters can be of any type. Subscripts can also return a value of any type.
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 * columns) + column]
}
set {
assert(indexIsValid(row: 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] = 3.2You can also define subscripts that are called on the type itself. This kind of subscript is called a type subscript.
enum Planet: Int {
case mercury = 1
case venus, earth, mars, jupiter, saturn, uranus, neptune
static subscript(n: Int) -> Planet {
return Planet(rawValue: n)!
}
}
let mars = Planet[4]
print(mars)