“线程 1：致命错误：索引超出范围”错误无法解决

Question

I am following the swiftris tutorial here: https://www.bloc.io/tutorials/swiftris-build-your-first-ios-game-with-swift#!/chapters/679

This tutorial was built for xcode 7, but i am using xcode 10. I have an error, Thread 1: Fatal error: Index out of range, that I cant seem to resolve. Here is my code:

class Array2D<T> {
      let columns: Int
      let rows: Int
 // #2
      var array: Array<T?>

      init(columns: Int, rows: Int) {
          self.columns = columns
          self.rows = rows
 // #3
        array = Array<T?>(unsafeUninitializedCapacity:rows * columns, initializingWith: {_,_ in })
      }

 // #4
      subscript(column: Int, row: Int) -> T? {
        get {
            return array[(row * columns) + column]
        }
          set(newValue) {
              array[(row * columns) + column] = newValue
          }
      }
  }

Thank you in advance!

Answer 1

Try changing the line at #3 as shown below:

     init(columns: Int, rows: Int) {
         self.columns = columns
         self.rows = rows
// #3
         array = Array<T?>(repeating: nil, count: rows * columns)
     }

init(unsafeUninitializedCapacity:initializingWith:) is not for usual use cases.

---

Generally Xcode 7 (Swift 2) is too....o old in the Swift world and you should better find an up-to-date tutorial.

Answer 2

In the later versions of Swift there is no need to do this as you can create a 2D array directly through 'an array or arrays' like let matrix = [[Int]].

However it is still a good exercise to code your own to understand how arrays and indexing work.

There are two things that could/should be changed from the example. Initialises the underlying array with .init(repeating: count:) and change the subscripting indexing as it currently doesn't work.

For a 0-indexed array with x rows and y columns, ie one ranging from (0,0) to (x-1, y-1)

class Array2D<T> {
   let columns: Int
   let rows: Int
   var array: Array<T?>

   init(columns: Int, rows: Int) {
      self.columns = columns
      self.rows = rows
      array = Array<T?>(repeating: nil, count: rows * columns)
   }

   subscript(column: Int, row: Int) -> T? {
      guard row <= rows && column <= columns else {fatalError("invalid position"))
      get {
         return array[(column * columns) + row]
      }
      set(newValue) {
         array[(column * columns) + row] = newValue
      }
   }
}

For a 1-indexed array, ie (1,1) through to (x,y) you'd need to change the subscripting to:

   subscript(column: Int, row: Int) -> T? {
      guard row < rows && column < columns else {fatalError("invalid position"))

      get {
         return array[((column - 1) * columns) + (row - 1)]
      }
      set(newValue) {
         array[((column - 1) * columns) + (row - 1)] = newValue
      }
   }