Putting it all together

struct AccountNumber {
    let number: String
    
    init?(untrustedAccountNumber: Untrusted<String>) {
        guard let validAcountNumber = AccountNumberValidator.validate(untrusted: untrustedAccountNumber)
            else {
                return nil
            }
        
        self.number = validAcountNumber
    }
}

struct AccountNumberValidator: Validator {
    static func validation(value: String) -> Bool {
        return isValidAccountNumber(value)
    }
}