基本上，把switch,用设计模式代替，肯定是bug和过度设计。想想，本来修改一个文件几行代码可以解决的问题，变成修改3-6个类才能实现一样的功能。不是傻是什么？

那些迷信设计模式的人，来修改一下这个方法吧。看看你最终的代码膨胀为几倍。。。

   public virtual PasswordChangeResult ChangePassword(ChangePasswordRequest request)
     {
         if (request == null)
             throw new ArgumentNullException("request");

         var result = new PasswordChangeResult();
         if (String.IsNullOrWhiteSpace(request.Email))
         {
             result.AddError(_localizationService.GetResource("Account.ChangePassword.Errors.EmailIsNotProvided"));
             return result;
         }
         if (String.IsNullOrWhiteSpace(request.NewPassword))
         {
             result.AddError(_localizationService.GetResource("Account.ChangePassword.Errors.PasswordIsNotProvided"));
             return result;
         }

         var customer = _customerService.GetCustomerByEmail(request.Email);
         if (customer == null)
         {
             result.AddError(_localizationService.GetResource("Account.ChangePassword.Errors.EmailNotFound"));
             return result;
         }

         var requestIsValid = false;
         if (request.ValidateRequest)
         {
             //password
             string oldPwd = "";
             switch (customer.PasswordFormat)
             {
                 case PasswordFormat.Encrypted:
                     oldPwd = _encryptionService.EncryptText(request.OldPassword);
                     break;
                 case PasswordFormat.Hashed:
                     oldPwd = _encryptionService.CreatePasswordHash(request.OldPassword, customer.PasswordSalt, _customerSettings.HashedPasswordFormat);
                     break;
                 default:
                     oldPwd = request.OldPassword;
                     break;
             }

             bool oldPasswordIsValid = oldPwd == customer.Password;
             if (!oldPasswordIsValid)
                 result.AddError(_localizationService.GetResource("Account.ChangePassword.Errors.OldPasswordDoesntMatch"));

             if (oldPasswordIsValid)
                 requestIsValid = true;
         }
         else
             requestIsValid = true;

         //at this point request is valid
         if (requestIsValid)
         {
             switch (request.NewPasswordFormat)
             {
                 case PasswordFormat.Clear:
                     {
                         customer.Password = request.NewPassword;
                     }
                     break;
                 case PasswordFormat.Encrypted:
                     {
                         customer.Password = _encryptionService.EncryptText(request.NewPassword);
                     }
                     break;
                 case PasswordFormat.Hashed:
                     {
                         string saltKey = _encryptionService.CreateSaltKey();
                         customer.PasswordSalt = saltKey;
                         customer.Password = _encryptionService.CreatePasswordHash(request.NewPassword, saltKey, _customerSettings.HashedPasswordFormat);
                     }
                     break;
                 default:
                     break;
             }
             customer.PasswordFormat = request.NewPasswordFormat;
             _customerService.UpdateCustomer(customer);
         }

         return result;
     }