5_DIP_code_refactor.md

refactor dependencies out into general interfaces

interface ILogger {
    void LogEvent(string event);
}
interface IMailService {
    void SendWelcomeEmail(Customer customer);
}

Then create specific concreate implementations that can be tested:

class TextFileLogger : ILogger {
  void LogEvent(string event) {
    /* write to a file on disk */
  }
}

class MailchimpEmailService : IMailService {
  void SendWelcomeEmail(Customer customer) {
    /* connect to Mailchimp API and send email to customer.email */
  }
}

The customer class should not rely on the concrete implementations, but rather the interfaces:

class CustomerService {
  private ILogger _logger;
  private IMailService _mailer;
  public CustomerService(ILogger logger, IMailService mailService) {
    this._logger = logger;
    this._mailer = mailService;
  }

  void ActivateLogin(Customer customer) {
    this._logger.logEvent("Customer " + customer.name + " is being activated");
    this._mailer.SendWelcomeEmail(customer);
  }
}

We can now easliy swap out the dependencies for different implementations with no changes to the CustomerService

« back to readme.md