Validating PhoneNumber type in Swift with a failable initialiser and an enum (for type safety)

phone.swift

import Foundation

typealias RegexPattern = String

let aussiePhoneNumber = 0424_555_123
let brokePhoneNumber = 0424_555_1231

enum PhoneNumberType: RegexPattern {
    // List all regex patterns
    case AussieMobile = "(?:\\+?61|0)4(?:[01]\\d{3}|(?:2[1-9]|3[0-57-9]|4[7-9]|5[0-15-9]|6[679]|7[3-8]|8[1478]|9[07-9])\\d{2}|(?:20[2-9]|444|52[0-6]|68[3-9]|70[0-7]|79[01]|820|890|91[0-4])\\d|(?:200[0-3]|201[01]|8984))\\d{4}$"
    // case ...
    // case ...

    // Helper
    var regexVal: RegexPattern { return self.rawValue }
}

private extension Int {
    func isA(type: PhoneNumberType) -> Bool {
        let matches = self.numberOfMatches(regex: type.regexVal)
        return matches > 0
    }
    func numberOfMatches(regex regexPattern: RegexPattern, options: NSRegularExpressionOptions = [], minimumIntegerDigits: Int = 20) -> Int?  {
        let formatter = NSNumberFormatter()
        formatter.minimumIntegerDigits = minimumIntegerDigits
        
        guard let
            nStr = formatter.stringFromNumber(self), // Create a n-character string with leading zeros
            regex = try? NSRegularExpression(pattern: regexPattern, options: options)
            else { return nil }
        
        let len = nStr.lengthOfBytesUsingEncoding(NSUTF8StringEncoding)
        return regex.numberOfMatchesInString(nStr, options: [], range: NSMakeRange(0, len))
    }
}

struct PhoneNumber {
    let number: Int
    init?(_ number: Int, phoneNumberType: PhoneNumberType) {
        guard number.isA(phoneNumberType) else { return nil }
        self.number = number
    }
}

PhoneNumber(aussiePhoneNumber, phoneNumberType: .AussieMobile) // Optional<PhoneNumber>(PhoneNumber(0424_555_123))
PhoneNumber(brokePhoneNumber, phoneNumberType: .AussieMobile)  // nil