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Hands-On Dependency Injection in Go
Hands-On Dependency Injection in Go

Hands-On Dependency Injection in Go: Develop clean Go code that is easier to read, maintain, and test

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Hands-On Dependency Injection in Go

SOLID Design Principles for Go

In 2002, Robert "Uncle Bob" Martin published the book Agile Software Development, Principles, Patterns, and Practices in which he defined the five principles of reusable programs, which he called SOLID principles. While it might seem strange to include these principles in a book about a programming language invented 10 years later, these principles are still relevant today.

In this chapter, we will briefly examine each of these principles, how they relate to dependency injection (DI) and what that means for Go. SOLID is an acronym for five popular object-oriented software design principles:

  • Single responsibility principle 
  • Open/closed principle 
  • Liskov substitution principle 
  • Interface segregation principle 
  • Dependency inversion principle 

Technical requirements

Single responsibility principle (SRP)

"A class should have one, and only one, reason to change."
                                                                                     –Robert C. Martin

Go doesn't have classes, but if we squint a little and replace the word class with objects (structs, functions, interfaces or packages), then the concept still applies.

Why do we want our objects to do only one thing? Let's look at a couple of objects that do one thing:

These objects are simple and easy to use, and have a wide range of uses.

Designing objects so that they all do only one thing sounds okay in the abstract....

Open/closed principle (OCP)

"Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification."
                                                                                                                                                       - Bertrand Meyer

The terms open and closed are not something I often hear when discussing software engineering, so perhaps they could do with a little explanation.

Open means that we should be able...

Liskov substitution principle (LSP)

"If for each object o1 of type S there is an object o2 of type T such that for all programs P defined in terms of T, the behavior of P is unchanged when o1 is substituted for o2 then S is a subtype of T."
                                                                                                                   -Barbara Liskov

After reading that three times, I am still not sure I have got it straight. Thankfully, Robert C. Martin made it easier on us and summarized it as follows:

"Subtypes must be substitutable for their base types...

Interface segregation principle (ISP)

"Clients should not be forced to depend on methods they do not use."
                                                                                                         –Robert C. Martin

Personally, I prefer a much more direct definition—interfaces should be reduced to the minimum possible size

Let's first discuss why fat interfaces might be a bad thing. Fat interfaces have more methods and are therefore likely to be harder to understand. They also require more work to use, whether this be through implementing, mocking, or stubbing them.

Fat...

Dependency inversion principle (DIP)

"High level modules should not depend on low level modules. Both should depend on abstractions. Abstractions should not depend upon details. Details should depend on abstractions"
                                                                                                             –Robert C. Martin

Have you ever found yourself standing in a shoe store wondering if you should get the brown or the black pair, only to get home and regret your choice? Sadly, once you've bought them, they're yours. Programming against concrete implementations...

Summary

In this brief introduction of SOLID design principles, we learned how they apply not only to DI, but also to Go. During our examination of the various DI methods in the second section of this book, we will frequently reference these principles.

In the next chapter, we will continue to examine the aspects of coding that should be at the forefront of your mind when studying and experimenting with new techniques. I will also introduce you to a few handy tools that will make your coding life a little easier.

Questions

  1. How does the single responsibility principle improve Go code?
  2. How does the open/closed principle improve Go code?
  3. How does the liskov substitution principle improve Go code?
  4. How does the interface segregation principle improve Go code?
  5. How does the dependency inversion principle improve Go code?
  6. How is dependency inversion different from dependency injection?

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Key benefits

  • • Learn to evaluate Code UX and make it better
  • • Explore SOLID principles and understand how they relate to dependency injection
  • • Use Google's wire framework to simplify dependence management

Description

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.

Who is this book for?

Hands-On Dependency Injection in Go is for programmers with a few year s experience in any language and a basic understanding of Go. If you wish to produce clean, loosely coupled code that is inherently easier to test, this book is for you.
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Table of Contents

14 Chapters
Never Stop Aiming for Better Chevron down icon Chevron up icon
SOLID Design Principles for Go Chevron down icon Chevron up icon
Coding for User Experience Chevron down icon Chevron up icon
Introduction to the ACME Registration Service Chevron down icon Chevron up icon
Dependency Injection with Monkey Patching Chevron down icon Chevron up icon
Dependency Injection with Constructor Injection Chevron down icon Chevron up icon
Dependency Injection with Method Injection Chevron down icon Chevron up icon
Dependency Injection by Config Chevron down icon Chevron up icon
Just-in-Time Dependency Injection Chevron down icon Chevron up icon
Off-the-Shelf Injection Chevron down icon Chevron up icon
Curb Your Enthusiasm Chevron down icon Chevron up icon
Reviewing Our Progress Chevron down icon Chevron up icon
Assessment Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

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Full star icon Full star icon Full star icon Full star icon Half star icon 4.4
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4 star 30%
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2 star 10%
1 star 0%
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Mike C Mar 04, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This is the kind of book I wish I'd had when I was starting out with Go. It is one thing to be familiar with best practices in software development in general, but quite another to be able to apply it with a new programming language. As the author explains, naively bringing patterns from other languages isn't going to work with Go - it will lead to frustration and subpar results.Although the book's main focus is Dependency Injection (DI), many other design principles are covered along the way, and reading this made me realise how fundamental DI is to writing good Go code. This is a very practical book, and it contains a wealth of code and examples that can actually be used day-to-day.One of the things I appreciated most about this book is how the author balances both the advantages and disadvantages of the techniques described. No solution is perfect, and it is important to know the potential problems and pitfalls you might face before implementing a new idea.The benefits claimed by reading this book should appeal to every Go professional: more readable, maintainable and testable code. Those reading your code in future - your colleagues, or your future self - will thank you!
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Amazonas Jan 17, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I have never used Go professionally but that din't stop me from enjoying this book. It goes over so many topics that everyone dealing with software need to know. I especially enjoyed how it tied DI to the SOLID principle and encouraged everyone to think about when DI might not be the right choice. A very balanced account on how DI can make your life easier with lots of examples that are easy to grasp but with enough details that can be used in everyday problems.
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Kindle Customer Jan 23, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Writing code in Golang is easy, but it takes some extra effort to write maintainable and sustainable code. Well, nothing lasts forever and it's more true for code, but surely you don't want to curse yourself for what you did just 4 or 6 months back. Dependency Injection is something which is essential if you want to make your code (unit)testable which will result into maintainable code. For example, if your codebase has 80% unit test coverage, you can make changes in a more confident manner by making less mistakes.Corey has been using Golang for over four years, and I know he is someone who is not afraid of trying new things and making mistakes. As he has real-life experience of working on a system developed using golang from scratch and which grew large (100x maybe) and he faced every possible pain in the journey. But it never stopped him to his endeavor to be a better software craftsman. I am happy to see he could put lot of his hard learned lessons into the book for the greater good of golang developers.This book is very important for working professionals. If you are already working on something where you are using Golang, you could reflect about your work while reading this book. I hope you can take something valuable out of it and apply in your system, maybe some good amount of refactoring - which will result in a more robust and maintainable system, and happiness.As software engineering is both art and science, it's very difficult to prescribe a single solution for a problem. Corey did a good job explaining DI from different angles - but still if you are a practicing golang developer, you may have different opinions about some of the topics/examples. So, I would request the reader not to get discouraged or confused by this, having an open mind helps.I wish all the best for this book and knowing the author, I hope he will continue iterating this book as he continues his journey as a software craftsman.[Disclaimer - I am a colleague of the author and due to my impression, I might be positively biased as a reader].
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regularbuyer Apr 11, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I have been writing golang for a year, but haven't put much serious thoughts in how to write my code better. By reading the first few chapters of this book, I have already gained some useful insights. The book showed useful examples of how to improve the structure of code with dependency injection. I highly recommend this book for anyone interested in improving his craft.
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Mark Angelo Feb 25, 2019
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This book is very helpful and has covered many ways on how to work your way and develop good code in Golang. As a developer coming from Java world, it is quite common to make mistakes in writing it the Java way and having conventions that I am already used to. This books has helped me basically get more comfortable writing code the Golang way. Dependency injection definitely needs to be part of the development and knowing how to do it the right way in Golang is really important. I recommend this book for everyone who would like to explore the possibilities of dependency injection in Golang.
Amazon Verified review Amazon
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