Hands-On Dependency Injection in Go

Method injection

Method injection is everywhere. You probably use it every day and you don't even realize it. Have you ever written code like this?:

fmt.Fprint(os.Stdout, "Hello World")

How about this?:

req, err := http.NewRequest("POST", "/login", body)

This is method injection—the passing in of the dependency as a parameter to the request.

Let's examine the previous examples in more detail. The function signature for Fprint() is as follows:

// Fprint formats using the default formats for its operands and writes // to w. It returns the number of bytes written and any write error // encountered.func Fprint(w io.Writer, a ...interface{}) (n int, err error)

As you can see, the first parameter, io.Writer, is a dependency for this function. What ...