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 emptyDictionary = [String: String]()
var populatedDictionary = ["key1": "value1", "key2": "value2"]
Note: if you are going to change the contents of the dictionary over time then declare it as a var (variable). You can declare an empty dictionary as a let (constant) but it is pointless if you have the intention of changing its contents over time, since constant can't be changed after it has been initialized.
Old answer:
Creating an empty dictionary of type <String, String> would look as follows:
var emptyDictionary = Dictionary<String, String>()
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.
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.
Use this will work.
var emptyDict = [String: String]()
You can simply declare it like this:
var emptyDict:NSMutableDictionary = [:]
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
Swift:
var myDictionary = Dictionary<String, AnyObject>()
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"
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()
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()
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>>()
If you want to create a generic dictionary with any type
var dictionaryData = [AnyHashable:Any]()
I'm usually using
var dictionary:[String:String] = [:]
dictionary.removeAll()
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"]
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] = [:]
var dictList = String:String for dictionary in swift var arrSectionTitle = String for array in swift
It is very handy for finding your way
var dict:Dictionary = [:]
var parking = [Dictionary < String, Double >()]
^ this adds a dictionary for a [string:double] input
来源：https://stackoverflow.com/questions/24033393/swift-declare-an-empty-dictionary