How to insert values into a nested Swift Dictionary - dictionary

Question

I'm trying to insert new key-value pair in dictionary, which nested in another one Dictionary:
var dict = Dictionary<Int, Dictionary<Int, String>>()
dict.updateValue([1 : "one", 2: "two"], forKey: 1)
dict[1]?[1] // {Some "one"}
if var insideDic = dict[1] {
// it is a copy, so I can't insert pair this way:
insideDic[3] = "three"
}
dict // still [1: [1: "one", 2: "two"]]
dict[1]?[3] = "three" // Cannot assign to the result of this expression
dict[1]?.updateValue("three", forKey: 3) // Could not find a member "updateValue"
I believe should be a simple way to handle it, but I spent an hour and still can't figure it out.
I can use NSDictionary instead, but I really like to understand how I should manage nested Dictionaries in Swift?

Answer 1

Dictionarys are value types so are copied on assignment. As a result you are going to have to get the inner dictionary (which will be a copy), add the new key, then re-assign.
// get the nested dictionary (which will be a copy)
var inner:Dictionary<Int, String> = dict[1]!
// add the new value
inner[3] = "three"
// update the outer dictionary
dict[1] = inner
println(dict) // [1: [1: one, 2: two, 3: three]]
You could use one of the new utility libraries such as ExSwift to make this a bit simpler:
dict[1] = dict[1]!.union([3:"three"])
This uses the union method that combines two dictionaries.