How to create a fixed-size array of objects

Question

In Swift  I am trying to create an array of 64 SKSpriteNode  I want first to initialize it empty  then I would put Sprites in the first 16 cells  and the last 16 cells  simulating an chess game    From what I understood in the doc  I would have expect something like   var sprites   SKSpriteNode   64    or  var sprites4   SKSpriteNode 64    But it doesn t work   In the second case  I get an error saying   Fixed-length arrays are not yet supported   Can that be real  To me that sounds like a basic feature  I need to access the element directly by their index

User · Answer

Swift 4

You can somewhat think about it as array of object vs. array of references.

[SKSpriteNode] must contain actual objects
[SKSpriteNode?] can contain either references to objects, or nil

Examples

Creating an array with 64 default SKSpriteNode:

var sprites = [SKSpriteNode](repeatElement(SKSpriteNode(texture: nil),
                                           count: 64))

Creating an array with 64 empty slots (a.k.a optionals):

var optionalSprites = [SKSpriteNode?](repeatElement(nil,
                                      count: 64))

Converting an array of optionals into an array of objects (collapsing [SKSpriteNode?] into [SKSpriteNode]):
```
let flatSprites = optionalSprites.flatMap { $0 }
```
The count of the resulting flatSprites depends on the count of objects in optionalSprites: empty optionals will be ignored, i.e. skipped.

User · Answer

Declare an empty SKSpriteNode  so there won t be needing for unwraping  var sprites    SKSpriteNode  count  64  repeatedValue  SKSpriteNode

User · Answer

Fixed-length arrays are not yet supported  What does that actually mean  Not that you can t create an array of n many things     obviously you can just do let a     1  2  3   to get an array of three Ints  It means simply that array size is not something that you can declare as type information   If you want an array of nils  you ll first need an array of an optional type      SKSpriteNode    not  SKSpriteNode      if you declare a variable of non-optional type  whether it s an array or a single value  it cannot be nil   Also note that  SKSpriteNode   is different from  SKSpriteNode      you want an array of optionals  not an optional array    Swift is very explicit by design about requiring that variables be initialized  because assumptions about the content of uninitialized references are one of the ways that programs in C  and some other languages  can become buggy  So  you need to explicitly ask for an  SKSpriteNode   array that contains 64 nils   var sprites    SKSpriteNode   repeating  nil  count  64    This actually returns a  SKSpriteNode     though  an optional array of optional sprites   A bit odd  since init count  repeatedValue   shouldn t be able to return nil   To work with the array  you ll need to unwrap it  There s a few ways to do that  but in this case I d favor optional binding syntax   if var sprites    SKSpriteNode   repeating  nil  count  64       sprites 0    pawnSprite

User · Answer

For now  semantically closest one would be a tuple with fixed number of elements   typealias buffer         SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode      SKSpriteNode  SKSpriteNode  SKSpriteNode  SKSpriteNode    But this is  1  very uncomfortable to use and  2  memory layout is undefined   at least unknown to me

User · Answer

If what you want is a fixed size array  and initialize it with nil values  you can use an UnsafeMutableBufferPointer  allocate memory for 64 nodes with it  and then read write from to the memory by subscripting the pointer type instance  This also has the benefit of avoiding checking if the memory must be reallocated  which Array does  I would however be surprised if the compiler doesn t optimize that away for arrays that don t have any more calls to methods that may require resizing  other than at the creation site  let count   64 let sprites   UnsafeMutableBufferPointer lt SKSpriteNode gt  allocate capacity  count   for i in 0   lt count       sprites i           for sprite in sprites       print sprite      sprites deallocate    This is however not very user friendly  So  let s make a wrapper  class ConstantSizeArray lt T gt   ExpressibleByArrayLiteral            typealias ArrayLiteralElement   T          private let memory  UnsafeMutableBufferPointer lt T gt           public var count  Int           get               return memory count                          private init   count  Int            memory   UnsafeMutableBufferPointer allocate capacity  count                 public convenience init count  Int  repeating value  T            self init count                   memory initialize repeating  value                 public required convenience init arrayLiteral  ArrayLiteralElement               self init arrayLiteral count                   memory initialize from  arrayLiteral                 deinit           memory deallocate                  public subscript index  Int  - gt  T           set value                precondition  0   endIndex  contains index                            memory index    value                    get               precondition  0   endIndex  contains index                            return memory index                     extension ConstantSizeArray  MutableCollection       public var startIndex  Int           return 0                public var endIndex  Int           return count - 1                func index after i  Int  - gt  Int           return i   1           Now  this is a class  and not a structure  so there s some reference counting overhead incurred here  You can change it to a struct instead  but because Swift doesn t provide you with an ability to use copy initializers and deinit on structures  you ll need a deallocation method  func release     memory deallocate       and all copied instances of the structure will reference the same memory  Now  this class may just be good enough  Its use is simple  let sprites   ConstantSizeArray lt SKSpriteNode  gt  count  64  repeating  nil   for i in 0   lt sprites count       sprite i           for sprite in sprites       print sprite      For more protocols to implement conformance to  see the Array documentation  scroll to Relationships

User · Answer

One thing you could do would be to create a dictionary  Might be a little sloppy considering your looking for 64 elements but it gets the job done  Im not sure if its the  preferred way  to do it but it worked for me using an array of structs   var tasks    0  forTasks    1  forTasks    2  forTasks    3  forTasks    4  forTasks    5  forTasks    6  forTasks

User · Answer

This question has already been answered  but for some extra information at the time of Swift 4   In case of performance  you should reserve memory for the array  in case of dynamically creating it  such as adding elements with Array append     var array    SKSpriteNode    array reserveCapacity 64   for   in 0   lt 64       array append SKSpriteNode        If you know the minimum amount of elements you ll add to it  but not the maximum amount  you should rather use array reserveCapacity minimumCapacity  64

User · Answer

The best you are going to be able to do for now is create an array with an initial count repeating nil   var sprites    SKSpriteNode   count  64  repeatedValue  nil    You can then fill in whatever values you want     In Swift 3 0    var sprites    SKSpriteNode   repeating  nil  count  64

[swift] How to create a fixed-size array of objects

Swift 4

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