Create a Dictionary as a optional property using Swift - ios

Question

I created a swift class to test Dictionaries. So, I wrote the code below:
import Foundation
class MyClass {
var myFirstDictionary:[String :String]
var myThirdDictionary:[String :String]?
init(){
var mySecondDictionary:[String :String] = [String :String]()
mySecondDictionary["animal"] = "Monkey"
mySecondDictionary.updateValue("something", forKey: "SomeKey")
self.myFirstDictionary = [String :String]()
addOneThingToSecondDictionary()
addAnotherThingToSecondDictionary()
self.myThirdDictionary! = [String :String]()
addOneThingToThirdDictionary()
addAnotherThingToThirdDictionary()
}
func addOneThingToSecondDictionary(){
self.myFirstDictionary["animal"] = "Monkey"
}
func addAnotherThingToSecondDictionary(){
self.myFirstDictionary.updateValue("Superman", forKey: "hero")
}
func addOneThingToThirdDictionary(){
self.myThirdDictionary["animal"]! = "Monkey"
}
func addAnotherThingToThirdDictionary(){
self.myThirdDictionary!.updateValue("Superman", forKey: "hero")
}
}
So, I got 3 errors referring to "myThirdDictionary" :
In the Dictionary initialization compiler said: Could not find an overload for 'init' that accepts the supplied arguments
When I tried to add a Key/value pair in addOneThingToThirdDictionary() : '[String : String]?' does not have a member named 'subscript'
When I tried to add a Key/value pair in addAnotherThingToThirdDictionary() : Immutable value of type '[String : String]' only has mutating members named 'updateValue'
Any thoughts ?

Answer 1

Some of these issues are conceptual errors, and some of them have to do with behaviors that changed in today's Xcode 6 beta 5 release. Running through them all:
This line compiles, but has a superfluous !:
self.myThirdDictionary! = [String :String]()
You don't need to unwrap an optional to assign to it -- it doesn't matter if its current contents are nil if you're providing new contents. Instead, just assign:
self.myThirdDictionary = [String :String]()
Similarly, this line fails because you're subscripting before unwrapping:
self.myThirdDictionary["animal"]! = "Monkey"
This is a problem because you could be subscripting nil if myThirdDictionary has not been initialized. Instead, subscript after checking/unwrapping the optional. As of beta 5, you can use mutating operators or methods through an optional check/unwrap, so the shortest and safest way to do this is:
self.myThirdDictionary?["animal"] = "Monkey"
If myThirdDictionary is nil, this line has no effect. If myThirdDictionary has been initialized, the subscript-set operation succeeds.
This line failed on previous betas because force-unwrapping produced an immutable value:
self.myThirdDictionary!.updateValue("Superman", forKey: "hero")
Now, it works -- sort of -- because you can mutate the result of a force-unwrap. However, force unwrapping will crash if the optional is nil. Instead, it's better to use the optional-chaining operator (which, again, you can now mutate through):
self.myThirdDictionary?.updateValue("Superman", forKey: "hero")
Finally, you have a lot of things in this code that can be slimmed down due to type and scope inference. Here it is with all the issues fixed and superfluous bits removed:
class MyClass {
var myFirstDictionary: [String: String]
var myThirdDictionary: [String: String]?
init(){
var mySecondDictionary: [String: String] = [:]
mySecondDictionary["animal"] = "Monkey"
mySecondDictionary.updateValue("something", forKey: "SomeKey")
myFirstDictionary = [:]
addOneThingToSecondDictionary()
addAnotherThingToSecondDictionary()
// uncomment to see what happens when nil
myThirdDictionary = [:]
addOneThingToThirdDictionary()
addAnotherThingToThirdDictionary()
}
func addOneThingToSecondDictionary(){
myFirstDictionary["animal"] = "Monkey"
}
func addAnotherThingToSecondDictionary(){
myFirstDictionary.updateValue("Superman", forKey: "hero")
}
func addOneThingToThirdDictionary(){
myThirdDictionary?["animal"] = "Monkey"
}
func addAnotherThingToThirdDictionary(){
myThirdDictionary?.updateValue("Superman", forKey: "hero")
}
}
(Changes: Foundation import unused, empty dictionary literal instead of repeated type info)

Answer 2

Simple but effective
let like = (dic.value(forKey: "likes") as? NSDictionary)
print(like?.count)
Or if you want get complete Dictionary count then use:
if let mainDic = dic as? NSDictionary{
print(mainDic.count)
//add your code
}