Initialising empty arrays of dictionaries in Swift

Question

I'm trying to wrap my head around initialising empty arrays in Swift.

For an array of strings it's pretty straight forward :

var myStringArray: String[] = [] myStringArray += "a" myStringArray += "b"  -> ["a", "b"] 

and for integers

var myIntArray: Int[] = [] myIntArray += 1 myIntArray += 2  -> [1, 2] 

it also works for other types of object such as NSImage objects :

let path = "/Library/Application Support/Apple/iChat Icons/Flags/" let image1 = NSImage(byReferencingFile: path + "Brazil.png") let image2 = NSImage(byReferencingFile: path + "Chile.png")  var myImageArray: NSImage[] = [] myImageArray += image1 myImageArray += image2  -> [<NSImage 0x7fe371c199f0 ...>, <NSImage 0x7fe371f39ea0 ...>] 

However I can't work out the syntax to initialise an empty array of Dictionaries.

I know you can have an array of Dictionaries because initialising with an initial value works :

let myDict1 = ["someKey":"someValue"] let myDict2 = ["anotherKey":"anotherValue"]  var myDictArray = [myDict1] myDictArray += myDict2  -> [["someKey": "someValue"], ["anotherKey": "anotherValue"]] 

This however (which you'd expect the syntax to be) fails :

var myNewDictArray: Dictionary[] = [] 

with the error Cannot convert the expression's type 'Dictionary[]' to type 'Hashable'

So the question is what is the correct way to initialise a empty array of Dictionary Items and why doesn't this syntax var myNewDictArray: Dictionary[] = [] work?

Answer 1

You need to give types to the dictionaries:

var myNewDictArray: [Dictionary<String, Int>] = [] 

or

var myNewDictArray = [Dictionary<String, Int>]() 

Edit: You can also use the shorter syntax:

var myNewDictArray: [[String:Int]] = [] 

or

var myNewDictArray = [[String:Int]]() 

Answer 2

This will create an empty, immutable dictionary:

let dictionary = [ : ]

And if you want a mutable one:

var dictionary = [ : ]

Both of these dictionaries default to Dictionary<String?, AnyObject?>.