Swift 3 conversion : value of type 'characterset' has no member 'characterIsMember'

In Swift 3, CharacterSet is re-designed to work well with UnicodeScalar rather than UTF-8 code point.

In this case, you can write something like this:

var containsAlphabets: Bool {
    //Checks if any of the characters inside the string are alphabets
    return self.unicodeScalars.contains {CharacterSet.letters.contains($0)}
}

Please try.

edit/update: Xcode 11.4 • Swift 5.1

extension StringProtocol {
    var containsLetters: Bool { contains { $0.isLetter } }
}