Swift 3.0 subscript for basic learning

preface

Classes, structs, and enums can all define subscripts that provide quick access to data member elements of a collection, list, or sequence. You can use someArray[index] To access Array, use someDictionary[key] Come visit Dictionary.

One type can define multiple subscripts.

Define 1 subscript of get set:

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

Define a subscript of read-only

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

Example:

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"

You can also use multiple subscripts of any type, except for parameters of type in-out

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
  }
 }
}

English text:
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Subscripts.html#//apple_ref/doc/uid/TP40014097-CH16-ID305

conclusion