Generate random passwords with OptionsSet

PasswordGenerator.swift

/**
 Generate random String of given size in Swift

 Given a size as n, generate a random alphanumeric String of this size.

 // elements of Swift CharacterSet are Unicode.Scalar and we cannot view the members so we cannot use CharacterSet.
 
 */

struct CharSet: OptionSet {
    let rawValue: Int
    // 1111, each bit represents one value
    static let lowercase: CharSet = CharSet(rawValue: 1 << 0)
    static let uppercase: CharSet = CharSet(rawValue: 1 << 1)
    static let numbers: CharSet = CharSet(rawValue: 1 << 2)
    static let symbols: CharSet = CharSet(rawValue: 1 << 3)
    
    static let all: CharSet = [.lowercase, .uppercase, .numbers, .symbols]
}

struct PasswordGenerator {
    
    var charSet: CharSet = .lowercase
    
    mutating func toggleOff(type: CharSet) {
        charSet.remove(type)
    }
    
    mutating func toggleOn(type: CharSet) {
        charSet.insert(type)
    }
    
    func generate(n: Int) -> String {
        assert(n <= 20, "Password too long")
        var possibleCharacters: [Character] = []
        if charSet.contains(.lowercase) {
            possibleCharacters.append(contentsOf: "abcdefghijklmnopqrstuvwxyz")
        }
        if charSet.contains(.uppercase) {
            possibleCharacters.append(contentsOf: "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
        }
        if charSet.contains(.numbers) {
            possibleCharacters.append(contentsOf: "0123456789")
        }
        if charSet.contains(.symbols) {
            possibleCharacters.append(contentsOf: "!\"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~")
        }
        var password: [Character] = []
        for _ in 0..<n {
            password.append(possibleCharacters.randomElement()!)
        }
        return String(password)
    }
}

var generator = PasswordGenerator()
generator.generate(n: 5)
generator.toggleOn(type: .uppercase)
generator.toggleOn(type: .symbols)
generator.toggleOn(type: .numbers)
generator.toggleOff(type: .symbols)
generator.generate(n: 10)