Hands-On Dependency Injection in Go

Constructor injection

When an object requires a dependency to work, the easiest way to ensure that dependency is always available is to require all users to supply it as a parameter to the object's constructor. This is known as constructor injection.

Let's work through an example where we will extract a dependency, generalize it, and achieve constructor injection. Say we are we are building a website for an online community. For this site, we wish to send an email to new users when they sign up. The code for this could be like this:

// WelcomeSender sends a Welcome email to new userstype WelcomeSender struct {   mailer *Mailer}func (w *WelcomeSender) Send(to string) error {   body := w.buildMessage()   return w.mailer.Send(to, body)}

We've made ...