Cannot subscript a value of type '[String : Int]' with an index of type 'String?'

Question

I have the following code. When it runs, it triggers the error : Cannot subscript a value of type '[String : Int]' with an index of type 'String?'

Can someone please help

self.books = self.books.filter { $0.completed[MUser.sharedInstance.getUserId()] ?? 0 > 0 }

completed is declared as

var completed = [String : Int]()

`getUserId()` is obviously an optional. The error says the key must be non-optional. Basically it's the same issue as in your [previous question](https://stackoverflow.com/questions/60196762/value-of-type-book-has-no-member-append). — vadian, Feb 13 '20 at 17:32
@LouisaScheinost What do you mean, "copy" an array? They are already [passed by value](https://stackoverflow.com/q/373419/9607863). — George, Feb 13 '20 at 17:40

score 1 · Accepted Answer · answered Feb 13 '20 at 17:40

The error indicates, that MUser.sharedInstance.getUserId() returns an optional.
You need to unwrap this:

self.books = self.books.filter {  
  guard let userID = MUser.sharedInstance.getUserId() else { return false }
  return $0.completed[userID] ?? 0 > 0 
}

Cannot subscript a value of type '[String : Int]' with an index of type 'String?'

1 Answers1