CODEWITHSUNDEEP
iosswiftdictionaryswift-optionals
plymr
plymr

Reputation: 45

Cannot assign value of type 'String??' to type 'String?' error

let say I defined a class

class Dummy {

    var title: String?
}

and I have a dictionary as

let foo: [Int: String?]  = [:]

then when I make an assignment as below

var dummy = Dummy()

dummy.title = foo[1]

it says

Cannot assign value of type 'String??' to type 'String?'

Insert ' as! String'

return type of foo is String? and Dictionary returns optional of its value type when used subscript but what is String?? type in swift?

I think it should be legal to make such assignment. Why it complains and how should I make this assignment

Upvotes: 0

Views: 981

Answers (2)

Paulw11
Paulw11

Reputation: 114783

By declaring your dictionary as [Int:String?] you are saying that the key is an Int and values are optional Strings. Now the key may not be present in the dictionary, so foo[1] optionally returns an optional and you end up with an with an optional optional - String??

Now while there are sometimes uses for optional optionals, I don't think that is what you want in this case.

You can simply make a dictionary of [Int:String] and then not insert an element if the value is nil. 

let foo: [Int: String]  = [:]
dummy.title = foo[1]

If you do need to handle the case where "there is a value for this key and it is nil" then the nil-coalescing operator may help you:

dummy.title = foo[1] ?? nil

or even

dummy.title = foo[1] ?? ""

Upvotes: 0

Frankenstein
Frankenstein

Reputation: 16341

Since having a value corresponding to the key 1 in the dictionary foo is optional and the value in the dictionary is of type String? it returns type String??. Unwrapping the value once to check if the value exists would fix this issue

if let value = foo[1] {
    dummy.title = value
}

Upvotes: 0

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