Creating the _validatePassword method

Register.dart

String _validatePassword(String pass1) {
  // 1
  RegExp hasUpper = RegExp(r'[A-Z]');
  RegExp hasLower = RegExp(r'[a-z]');
  RegExp hasDigit = RegExp(r'\d');
  RegExp hasPunct = RegExp(r'[!@#\$&*~-]');
  // 2
  if (!RegExp(r'.{8,}').hasMatch(pass1))
    return 'Passwords must have at least 8 characters';
  // 3
  if (!hasUpper.hasMatch(pass1))
    return 'Passwords must have at least one uppercase character';
  // 4
  if (!hasLower.hasMatch(pass1))
    return 'Passwords must have at least one lowercase character';
  // 5
  if (!hasDigit.hasMatch(pass1))
    return 'Passwords must have at least one number';
  // 6
  if (!hasPunct.hasMatch(pass1))
    return 'Passwords need at least one special character like !@#\$&*~-';
  // 7
  return null;
}