had the same problem, and a comment of Brad Dillon showed the solution:
var predicate:String
var wordsRequest : FetchRequest<Word>
var words : FetchedResults<Word>{wordsRequest.wrappedValue}
init(predicate:String){
self.predicate = predicate
self.wordsRequest = FetchRequest(entity: Word.entity(), sortDescriptors: [], predicate:
NSPredicate(format: "%K == %@", #keyPath(Word.character),predicate))
}
in this example, you can modify the predicate in the initializer.