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]()

Answer 1

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 
}