Book Image

Hands-On Dependency Injection in Go

By : Corey Scott
Book Image

Hands-On Dependency Injection in Go

By: Corey Scott

Overview of this book

Hands-On Dependency Injection in Go takes you on a journey, teaching you about refactoring existing code to adopt dependency injection (DI) using various methods available in Go. Of the six methods introduced in this book, some are conventional, such as constructor or method injection, and some unconventional, such as just-in-time or config injection. Each method is explained in detail, focusing on their strengths and weaknesses, and is followed with a step-by-step example of how to apply it. With plenty of examples, you will learn how to leverage DI to transform code into something simple and flexible. You will also discover how to generate and leverage the dependency graph to spot and eliminate issues. Throughout the book, you will learn to leverage DI in combination with test stubs and mocks to test otherwise tricky or impossible scenarios. Hands-On Dependency Injection in Go takes a pragmatic approach and focuses heavily on the code, user experience, and how to achieve long-term benefits through incremental changes. By the end of this book, you will have produced clean code that’s easy to test.
Table of Contents (15 chapters)

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 makes this different from any other function call is the fact that the dependency provides...