how to write function to evaluate if String is only characters? - swift

Question

I've seen other answers to this question, but I'm just trying to do it differently. Yet whatever I do I can't make my types match.
func ContainsOnlyAlphabets(_ word : String) -> Bool{
let letters = CharacterSet.letters // Set<Character>
let trimmed = word.trimmingCharacters(in: .whitespaces)
let characterViewArray = Array(trimmed.characters) // Array<characterView>
let characterArray = characterViewArray.map{Character($0)} // Error: Can't create Chars
let wordCharactersSet = Set(characterArray) // Set<Character>
let intersection = wordCharactersSet.intersection(letters)
return intersection.count == characterArray.count
}
I had to do all the Set,Char,String,Array conversions but still couldn't get it right :(.
cannot invoke initializer for type 'Character' with an argument list
of type '((String.CharacterView._Element))'

Answer 1

Your code
let characterViewArray = Array(trimmed.characters)
already creates a Array<Character>, so you could simple skip the
next line and create a Set<Character> with
let wordCharactersSet = Set(characterViewArray)
But that does not really help, because Set<Character> and
CharacterSet are different types, so that
let intersection = wordCharactersSet.intersection(letters)
does not compile. Possible alternatives are
return trimmed.rangeOfCharacter(from: letters.inverted) == nil
or
return CharacterSet(charactersIn: trimmed).isSubset(of: letters)
If your intention is to allow both letters and whitespace characters
then it could look like this:
func containsOnlyLettersAndWhitespace(_ word : String) -> Bool{
var allowedSet = CharacterSet.letters
allowedSet.formUnion(CharacterSet.whitespaces)
return word.rangeOfCharacter(from: allowedSet.inverted) == nil
// Alternatively:
return CharacterSet(charactersIn: word).isSubset(of: allowedSet.inverted)
}

Answer 2

As MartinR noted, CharacterSet is not equivalent to Set<Character>
The closest I could get to your original solution was to create a CharacterSet from the trimmed string and apply some of your original algorithm to that:
func ContainsOnlyAlphabets(_ word : String) -> Bool{
let letters = CharacterSet.letters
let trimmed = word.trimmingCharacters(in: .whitespaces)
let wordCharacterSet = CharacterSet(charactersIn:trimmed)
let intersection = wordCharacterSet.intersection(letters)
return intersection == wordCharacterSet
}
Keeping it strictly in the realm of CharacterSet and operations on that, you could also use:
func ContainsOnlyAlphabets(_ word : String) -> Bool{
return CharacterSet.letters.isSuperset(of:
CharacterSet(charactersIn: word.trimmingCharacters(in: .whitespaces))
)
}
That said, I think I'd still go with Martin's solution:
func ContainsOnlyAlphabets(_ word : String) -> Bool{
return word
.trimmingCharacters(in: .whitespaces)
.rangeOfCharacter(from: CharacterSet.letters.inverted) == nil
}
as being more intuitive.