[ios] Swift: declare an empty dictionary

I am beginning to learn swift by following the iBook-The Swift Programming Language on Swift provided by Apple. The book says to create an empty dictionary one should use [:] same as while declaring array as []:

I declared an empty array as follows :

let emptyArr = [] // or String[]()

But on declaring empty dictionary, I get syntax error:

let emptyDict = [:]

How do I declare an empty dictionary?

var parking = [Dictionary < String, Double >()]

^ this adds a dictionary for a [string:double] input

You can declare it as nil with the following:

var assoc : [String:String]

Then nice thing is you've already typeset (notice I used var and not let, think of these as mutable and immutable). Then you can fill it later:

assoc = ["key1" : "things", "key2" : "stuff"]

It is very handy for finding your way

var dict:Dictionary = [:]

Use this will work.

var emptyDict = [String: String]()

You have to give the dictionary a type

// empty dict with Ints as keys and Strings as values
var namesOfIntegers = Dictionary<Int, String>()

If the compiler can infer the type, you can use the shorter syntax

namesOfIntegers[16] = "sixteen"
// namesOfIntegers now contains 1 key-value pair
namesOfIntegers = [:]
// namesOfIntegers is once again an empty dictionary of type Int, String

I'm playing with this too. It seems strange that you can just declare an empty dictionary and then add a key/value pair to it like so :

var emptyDictionary = Dictionary<String, Float>()
var flexDictionary = [:]
emptyDictionary["brian"] = 4.5
flexDictionary["key"] = "value" // ERROR : cannot assign to the result of this expression

But you can create a Dictionary that accepts different value types by using the "Any" type like so :

var emptyDictionary = Dictionary<String, Any>()
emptyDictionary["brian"] = 4.5
emptyDictionary["mike"] = "hello"

If you want to create a generic dictionary with any type

var dictionaryData = [AnyHashable:Any]()

You can't use [:] unless type information is available.

You need to provide it explicitly in this case:

var dict = Dictionary<String, String>()

var means it's mutable, so you can add entries to it. Conversely, if you make it a let then you cannot further modify it (let means constant).

You can use the [:] shorthand notation if the type information can be inferred, for instance

var dict = ["key": "value"]

// stuff

dict = [:] // ok, I'm done with it

In the last example the dictionary is known to have a type Dictionary<String, String> by the first line. Note that you didn't have to specify it explicitly, but it has been inferred.

You need to explicitly tell the data type or the type can be inferred when you declare anything in Swift.

Swift 3

The sample below declare a dictionary with key as a Int type and the value as a String type.

Method 1: Initializer

let dic = Dictionary<Int, String>()

Method 2: Shorthand Syntax

let dic = [Int:String]()

Method 3: Dictionary Literal

var dic = [1: "Sample"]
// dic has NOT to be a constant
dic.removeAll()

You can simply declare it like this:

var emptyDict:NSMutableDictionary = [:]

Swift:

var myDictionary = Dictionary<String, AnyObject>()

Swift 4

let dicc = NSDictionary()

//MARK: - This is empty dictionary
let dic = ["":""]

//MARK:- This is variable dic means if you want to put variable 
let dic2 = ["":"", "":"", "":""]

//MARK:- Variable example
let dic3 = ["name":"Shakeel Ahmed", "imageurl":"https://abc?abc.abc/etc", "address":"Rawalpindi Pakistan"]

//MARK: - This is 2nd Variable Example dictionary
let dic4 = ["name": variablename, "city": variablecity, "zip": variablezip]

//MARK:- Dictionary String with Any Object
var dic5a = [String: String]()
//MARK:- Put values in dic
var dic5a = ["key1": "value", "key2":"value2", "key3":"value3"]

var dic5b = [String:AnyObject]()
dic5b = ["name": fullname, "imageurl": imgurl, "language": imgurl] as [String : AnyObject]

or
//MARK:- Dictionary String with Any Object
let dic5 = ["name": fullname, "imageurl": imgurl, "language": imgurl] as [String : AnyObject]

//MARK:- More Easy Way
let dic6a = NSDictionary()
let dic6b = NSMutalbeDictionary()

I'm usually using

var dictionary:[String:String] = [:]
dictionary.removeAll()

var dictList = String:String for dictionary in swift var arrSectionTitle = String for array in swift

You can use the following code:

var d1 = Dictionary<Int, Int>()
var d2 = [Int: Int]()
var d3: Dictionary<Int, Int> = [Int : Int]()
var d4: [Int : Int] = [:]

Declaring & Initializing Dictionaries in Swift

Dictionary of String

var stringDict: [String: String] = [String: String]()

OR

var stringDict: Dictionary<String, String> = Dictionary<String, String>()

Dictionary of Int

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

OR

var stringDict: Dictionary<String, Int> = Dictionary<String, Int>()

Dictionary of AnyObject

var stringDict: [String: AnyObject] = [String: AnyObject]()

OR

var stringDict: Dictionary<String, AnyObject> = Dictionary<String, AnyObject>()

Dictionary of Array of String

var stringDict: [String: [String]] = [String: [String]]()

OR

var stringDict: Dictionary<String, Array<String>> = Dictionary<String, Array<String>>()

Array of Dictionaries of String

var stringDict: [[String: String]] = [[String: String]]()

OR

var stringDict: Array<Dictionary<String, String>> = Array<Dictionary<String, String>>()

The Swift documentation recommends the following way to initialize an empty Dictionary:

var emptyDict = [String: String]()

I was a little confused when I first came across this question because different answers showed different ways to initialize an empty Dictionary. It turns out that there are actually a lot of ways you can do it, though some are a little redundant or overly verbose given Swift's ability to infer the type.

var emptyDict = [String: String]()
var emptyDict = Dictionary<String, String>()
var emptyDict: [String: String] = [:]
var emptyDict: [String: String] = [String: String]()
var emptyDict: [String: String] = Dictionary<String, String>()
var emptyDict: Dictionary = [String: String]()
var emptyDict: Dictionary = Dictionary<String, String>()
var emptyDict: Dictionary<String, String> = [:]
var emptyDict: Dictionary<String, String> = [String: String]()
var emptyDict: Dictionary<String, String> = Dictionary<String, String>()

After you have an empty Dictionary you can add a key-value pair like this:

emptyDict["some key"] = "some value"

If you want to empty your dictionary again, you can do the following:

emptyDict = [:]

The types are still <String, String> because that is how it was initialized.