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.

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Table of Contents (15 chapters)
Preface
Preface
Who this book is for
What this book covers
To get the most out of this book
Get in touch
Free Chapter
1
Never Stop Aiming for Better
Never Stop Aiming for Better
Technical requirements
Why does DI matter?
Code smells that indicate you might need DI
Healthy skepticism
A quick word about idiomatic Go
Leave your baggage at the door
Summary
Questions
Further reading
2
SOLID Design Principles for Go
SOLID Design Principles for Go
Technical requirements
Single responsibility principle (SRP)
Open/closed principle (OCP)
Liskov substitution principle (LSP)
Interface segregation principle (ISP)
Dependency inversion principle (DIP)
Summary
Questions
Further reading
3
Coding for User Experience
Coding for User Experience
Technical requirements
Optimizing for humans
A security blanket named unit tests
Test-induced damage
Visualizing your package dependencies with Godepgraph
Summary
Questions
4
Introduction to the ACME Registration Service
Introduction to the ACME Registration Service
Technical requirements
Goals for our system
Introduction to our system
Known issues
Summary
Questions
5
Dependency Injection with Monkey Patching
Dependency Injection with Monkey Patching
Technical requirements
Monkey magic!
Advantages of monkey patching
Applying monkey patching
When the magic fades
Summary
Questions
Further reading
6
Dependency Injection with Constructor Injection
Dependency Injection with Constructor Injection
Technical requirements
Constructor injection
Advantages of constructor injection
Applying constructor injection
Disadvantages of constructor injection
Summary
Questions
7
Dependency Injection with Method Injection
Dependency Injection with Method Injection
Technical requirements
Method injection
Advantages of method injection
Applying method injection
Disadvantages of method injection
Summary
Questions
8
Dependency Injection by Config
Dependency Injection by Config
Technical requirements
Config injection
Advantages of config injection
Applying config injection
Disadvantages of config injection
Summary
Questions
9
Just-in-Time Dependency Injection
Just-in-Time Dependency Injection
Technical requirements
JIT injection
Advantages of JIT injection
Applying JIT injection
Disadvantages of JIT injection
Summary
Questions
10
Off-the-Shelf Injection
Off-the-Shelf Injection
Technical requirements
Off-the-shelf injection with Wire
Advantages of off-the-shelf injection
Applying off-the-shelf injection
Disadvantages of off-the-shelf injection
Summary
Questions
11
Curb Your Enthusiasm
Curb Your Enthusiasm
Technical requirements
DI induced damage
Unnecessary injection
Summary
Questions
12
Reviewing Our Progress
Reviewing Our Progress
Technical requirements
Overview of the improvements
Review of the dependency graph
Review of test coverage and testability
Starting a new service with DI
Summary
Questions
13
Assessment
Assessment
Chapter 1, Never Stop Aiming for Better
Chapter 2, SOLID Design Principles for Go
Chapter 3, Coding for User Experience
Chapter 4, Introduction to the ACME Registration Service
Chapter 5, Dependency Injection with Monkey Patching
Chapter 6, Dependency Injection with Constructor Injection
Chapter 7, Dependency Injection with Method Injection
Chapter 8, Dependency Injection by Config
Chapter 9, Just-in-Time Dependency Injection
Chapter 10, Off-the-Shelf Injection
Chapter 11, Curbing Your Enthusiasm
Chapter 12, Reviewing Our Progress
14
Other Books You May Enjoy
Other Books You May Enjoy
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Chapter 9, Just-in-Time Dependency Injection

1. How does Just-in-Time (JIT) dependency injection differ from constructor injection?

This depends a lot on how the constructor injection is being used; in particular, how many different implementations of the dependency exist. If there is only one production implementation of a dependency, then they are functionally equivalent. The only difference is UX (that is, whether there is one less dependency to inject into the constructor).

If, however, there is more than one production implementation, then JIT dependency injection cannot be used.

 

2. When working with optional dependencies, why is using a NO-OP implementation important?

When a member variable is not set by the constructor, then it is effectively optional. We cannot, therefore, be sure that the value has been set and not nil. By adding a NO-OP implementation of the optional...

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