table of content

1 Meet Go

1.1 What is Go?

1.2 Why you should learn Go

1.2.1 How and where Go can help you

1.2.2 Where can Go cannot help you

1.2.3 Comparison with commonly used languages

1.3 Why pocket-sized projects?

1.3.1 What you’ll know after reading the book (and writing the code)

Summary

2 Hello, earth! Extend your hello, world

2.1 Any travel begins at home

2.1.1 Our first program: main.go

2.1.2 Let’s test with the Example function

2.1.3 Calling the greet function

2.1.4 Testing a specific function with the testing package

2.2 Are you a polyglot?

2.2.1 Parlez-vous français? The switch angle

2.2.2 Adapt the test with Test functions

2.3 Supporting more languages with a phrasebook

2.3.1 Introducing the Go map hash table

2.3.2 Writing a table-driven test

2.4 Using the flag package to read the user’s language

2.4.1 Add a flag

2.4.2 Test the command-line interface

2.5 Side quests

Summary

3 A bookworm’s digest: Playing with loops and maps

3.1 Loading the JSON data

3.1.1 Defining a JSON example

3.1.2 Opening a file

3.1.3 Parse the JSON

3.1.4 Test it

3.2 Finding books that bookworms have in common

3.2.1 Count the books

3.2.2 Keeping higher occurrences

3.2.3 Determinism

3.3 Print

3.4 Improvements

3.4.1 Implement sort.Interface

3.4.2 Exercise: Reading recommendations

3.4.3 Using bufio to open a file

Summary

4 A log story: Creating a library

4.1 Defining the API

4.1.1 Package summary

4.1.2 Exporting the supported levels

4.1.3 Object-oriented Go: “GoOOP”?

4.1.4 The New() function

4.1.5 What about testing?

4.1.6 Documenting code

4.2 Implementing the exported methods

4.2.1 Default implementation

4.2.2 Interfacing

4.2.3 Refactoring

4.3 The functional options pattern

4.3.1 Creating configurations

4.3.2 Testing our example

4.4 Additional functionalities

4.4.1 Logging the log level

4.4.2 Exposing the generic logging function

4.5 Logging: Best practices

Summary

5 Gordle: Play a word game in your terminal

5.1 Basic main version

5.1.1 Mini main

5.1.2 Read player’s input

5.1.3 Isolate the check

5.1.4 Check for victory

5.2 Providing feedback

5.2.1 Define character status

5.2.2 Checking a guess against the solution

5.3 Corpus

5.3.1 Create a list of words

5.3.2 Read the corpus

5.3.3 Pick a word

5.3.4 Let’s play!

5.4 The limit of runes

5.5 Conclusion

Summary

6 Money converter: CLI around an HTTP call

6.1 Business definitions

6.1.1 Converting money

6.2 Representing money

6.2.1 Floating-point numbers

6.2.2 Back to money

6.2.3 Floating-point number operations

6.2.4 Implementing decimals

6.2.5 Currency value object

6.2.6 NewAmount

6.3 Applying conversion logic

6.3.1 Applying an exchange rate

6.3.2 Validating the result

6.4 Writing the CLI

6.4.1 Flags and arguments

6.4.2 Parse into business types

6.4.3 Stringer

6.4.4 Convert

6.5 Calling the bank

6.5.1 Dependency injection: Theory

6.5.2 ECB package

6.5.3 HTTP call: Easy version

6.5.4 Parse the response

6.5.5 Integration in the money package

6.5.6 Dependency injection in main

6.5.7 Sharing the executable

6.6 Making improvements

6.6.1 Caching

6.6.2 Timeout

6.6.3 Alternative tree

Summary

7 Caching with generics

7.1 A naive cache

7.1.1 Introduction to generics

7.1.2 Project initialization

7.1.3 Implementation

7.2 Introducing goroutines

7.2.1 What’s a goroutine?

7.2.2 How to launch a goroutine

7.2.3 Using channels to communicate that a goroutine has ended

7.2.4 Running goroutines and having a synchronization point

7.3 A more thread-safe cache

7.3.1 Using goroutines

7.3.2 Using t.Parallel()

7.3.3 Using go test -race .

7.3.4 Add a mutex

7.4 Possible improvements

7.4.1 Adding time to live

7.4.2 Add a maximum number of items in the cache

7.5 Common mistakes

7.5.1 When to use channels in a concurrency situation

7.5.2 Concurrency effect of a workload type

7.5.3 Finish your goroutines

Summary

8 Gordle as a service

8.1 Empty shell for the new service

8.1.1 Server, service, web service, endpoints, and HTTP handlers

8.1.2 Let’s code

8.2 Adding endpoints

8.2.1 Create a new game

8.2.2 Get the game status

8.2.3 Guess

8.3 Domain objects

8.3.1 Domain types

8.3.2 API adapters

8.4 Repository

8.4.1 In-memory database

8.4.2 Simplest repository

8.4.3 Service-level dependency

8.4.4 Add a mutex to the repository

8.5 Adapting the Gordle library

8.5.1 API of the library

8.5.2 Usage in the endpoints

8.6 Security notions and improvements

8.6.1 Limiting the number of requests served at a time

8.6.2 User authentication

8.6.3 Logging

8.6.4 Error formatting

8.6.5 Decode query parameters

Summary

9 Concurrent maze solver

9.1 Maze generation

9.1.1 What is an image?

9.1.2 Maze constraints

9.2 Maze solver

9.2.1 Setup

9.2.2 Loading the maze image

9.2.3 Add the solver

9.3 Let’s go exploring!

9.3.1 Finding the entrance

9.3.2 Communicating new possible paths

9.3.3 Recording the explored path

9.3.4 Waiting for unexplored paths and starting a goroutine

9.3.5 Stop listening, we found it: Short version

9.3.6 Testing one goroutine’s logic

9.4 Show the result

9.5 Notify when the treasure is found

9.5.1 Keep track of all the goroutines

9.5.2 Send a quit signal

9.6 Visualization

9.6.1 Overcome the loop constraint

9.6.2 Animate the exploration

Summary

10 Habits tracker using gRPC

10.1 API definition

10.1.1 Protobuf declaration

10.1.2 Code generation

10.2 Empty service

10.2.1 Creating a small logger

10.2.2 Server structure

10.2.3 Creating and running the server

10.3 First endpoint: Create

10.3.1 Business layer

10.3.2 API layer

10.3.3 Data retention

10.4 Unit testing with generated mocks

10.4.1 Generate mocks

10.4.2 Use the mocks

10.5 Integration testing

10.5.1 List habits

10.5.2 Integration with go test

10.6 Getting the best out of the context

10.6.1 What is a context?

10.6.2 Create a context

10.6.3 Using a context

10.7 Track your habits

10.7.1 Tick a habit

10.7.2 Store ticks per week

10.7.3 Handle corner cases

10.7.4 Get habit status

10.7.5 Add a timestamp

10.7.6 Habit tracker in action

Summary

11 HTML templating with a gRPC client

11.1 Your basic HTTP server

11.1.1 Hello plain text

11.1.2 Templates: Display a variable

11.1.3 Add a gRPC client

11.2 Basic template operations

11.2.1 Iterate through a slice

11.2.2 Accessing fields

11.2.3 Conditional formatting

11.3 Send a tick to the server

11.3.1 What page should we display?

11.3.2 Send tick to the backend

11.3.3 Adding colors

11.4 Use a form to create a habit

11.4.1 HTML form

11.4.2 Read a form’s values

11.5 More template niceties

11.5.1 Passing more than one object to the template

11.5.2 Calling functions

11.5.3 Using define to declare functions

Summary

12 Go for other architectures

12.1 Getting started with Wasm

12.1.1 Some practice with Hello Wasm

12.1.2 Write a file server

12.2 Multiplication quiz project

12.2.1 Displaying random numbers on the HTML page

12.2.2 Registering functions in Go

12.2.3 Reading an input from the page

12.3 TinyGo

12.3.1 Building a simple TinyGo application

12.3.2 Differences with Go

12.3.3 Debugging and deploying with TinyGo

Summary

Appendixes

Appendix A: Installation steps

A.1 Install

A.2 Check

A.3 Go’s environment variables

A.3.1 The go env command

A.3.2 The GOBIN variable

A.3.3 The GOPATH variable

A.3.4 The GOROOT variable

A.4 Hello!

A.5 Installing new dependencies

A.5.1 go install

A.5.2 go get

A.6 Code editors

Appendix B: Formatting cheat sheet

Appendix C: Zero values

C.1 What is a zero value?

C.2 The zero values of any types

C.3 Slices and maps specificities

C.4 Benefiting from zero values

Appendix D: Benchmarking

Appendix E: Passing by value or by reference

E.1 Go passes everything by value

E.1.1 Copying parameters on the stack

E.1.2 Using pointers

E.1.3 Shallow copies

E.1.4 Functions vs. methods

E.2 Special types of parameters: slices, maps, and channels

E.2.1 Passing a slice as a parameter

E.2.2 maps, channels, and more

E.3 A few recommendations

E.3.1 Passing by value should be the default

E.3.2 Passing by pointer is a minor optimization

E.3.3 Passing by pointer when mutating

E.3.4 Using slices and maps

E.3.5 Passing a pointer to a slice or to a map

E.3.6 Writing your own Copy function

Appendix F: Fuzzing

F.1 A new testing method

F.2 How it works

F.3 Writing a first test

F.3.1 Function under test

F.3.2 Fuzz test

F.4 Running and interpreting fuzz tests

F.5 Fixing the breach

F.6 Best practices and common pitfalls

Appendix G: Connecting to a database

G.1 Setup

G.1.1 Starting a PostgreSQL database locally

G.1.2 Seed the schema

G.2 Repository package

G.2.1 Injecting a connection

G.2.2 Querying the database

G.3 Libraries

Overview

Appendix A. Installation steps

Getting started focuses on installing the Go toolchain and confirming your setup. The text notes that Go’s compiler and tools have been written in Go itself since 1.3 and are open source, encouraging exploration of the standard library. Installation is straightforward on Linux, macOS, and Windows: download the installer, add Go to your PATH, and favor the latest release (the book uses Go 1.23). You can verify a successful setup from any directory by checking the version to confirm that Go is properly installed and available on your system.

Go relies on environment settings with sensible defaults, all visible via the go env command. While you rarely need to change them, values can be overridden temporarily with standard environment variables or persisted using go env -w, which writes to the configuration file indicated by GOENV. Key variables include GOBIN (where binaries installed via go install are placed), GOPATH (the set of directories used for resolving and caching dependencies; ensure your workspace is included), and GOROOT (the Go installation directory; avoid modifying it and keep its bin directory on PATH for tools like go and gofmt).

To validate the toolchain, create a small Hello World program, initialize a module with go mod init, and run it with go run. From there, you can bring in external work in two complementary ways: go install fetches and builds command-line tools as binaries into GOBIN, supporting explicit versions, latest, or project-scoped resolution; go get retrieves source dependencies for your project, updates go.mod, and downloads code into the module cache, with support for tags, branches, or specific commits. With these essentials, you can install Go, understand its environment, run your first program, and manage tools and libraries confidently.

A.6 Code editors

Go is supported by more and more code editors. As always in this situation, the best tool is the one you know how to use. The official Go website, as we write, lists three editors:

GoLand, by JetBrains. JetBrains has a long list of editors for various languages, the most famous being IntelliJ for Java. You can install GoLand as a standalone editor or add the Go plugin to any other editor in the list.
Visual Studio Code, by Microsoft, has a Go extension.
vim-go is great if you already know vim

A quick search around the web will easily give you instructions to add Go support to your usual tool, if it is not already there, e.g. with GoSublime, Atom with GoPlus, LiteIDE…

Go is now installed on your machine and you can start using it and follow the book’s instructions. We learned about the Go environment variables and important paths. Your terminal knows how to greet you in English using Go, you can move to Chapter 2 and teach it to greet you in other human languages.

FAQ

How do I install Go on my system?

Visit https://go.dev/doc/install, download the installer for your OS (Linux, macOS, or Windows), run it, and add the Go binary directory to your PATH so the go command is available in your terminal.

Which Go version should I install?

Install the latest stable Go release. The book was written using Go 1.23, and there’s generally no good reason to pick older versions.

How can I verify that Go is installed correctly?

Open a terminal anywhere and run: go version. You should see output like: go version go1.xx.x youros/arch.

What does the go env command do?

go env prints Go-specific environment variables, including defaults even if you didn’t set them in your shell. You can list all, or limit output, for example: go env -json GOBIN GOENV GOROOT GOPATH CGO_ENABLED.

How do I change Go environment variables?

You can override them temporarily via standard env vars (e.g., on Linux: CGO_ENABLED=0 go env -json CGO_ENABLED) or persistently with: go env -w VARIABLE=VALUE. Persistent settings are stored in the file pointed to by GOENV.

What is GOBIN and how should I set it?

GOBIN is the directory where go install module@version puts compiled tool binaries. Set it with: go env -w GOBIN=/path/to/bin and ensure that directory is on your PATH so installed tools are runnable.

What is GOPATH and why does it matter?

GOPATH is a list of workspace directories Go uses, including where it caches dependencies (e.g., $GOPATH/pkg/mod). Make sure your workspace is included. Example: go env -w GOPATH=${GOPATH}:/path/to/workspace (on Windows use semicolons).

What is GOROOT and should I change it?

GOROOT points to the Go installation directory. Don’t modify its contents or point other Go vars inside it. Ensure ${GOROOT}/bin is on your PATH; it contains go and gofmt.

How do I write and run a simple “Hello, World!” in Go?

Create a folder (e.g., hello) with hello.go containing a main that prints “Hello, World!”. Initialize a module with: go mod init hello, then run: go run hello.go.

When should I use go install vs go get?

Use go install for tools/binaries (compiles for your machine): go install repo/path/cmd@version or @latest. Use go get inside a module to add source dependencies to go.mod (and download them to $GOPATH/pkg/mod): go get module@version, where version can be a tag, branch (e.g., @master), or commit.

pro $24.99 per month

access to all Manning books, MEAPs, liveVideos, liveProjects, and audiobooks!
choose one free eBook per month to keep
exclusive 50% discount on all purchases
renews monthly, pause or cancel renewal anytime

lite $19.99 per month

access to all Manning books, including MEAPs!

team

5, 10 or 20 seats+ for your team - learn more

eBook

pdf, ePub, online

$54.99 $27.49

you save $27.50 (50%)

include audio $24.99 $12.49

pro $24.99 per month

access to all Manning books, MEAPs, liveVideos, liveProjects, and audiobooks!
choose one free eBook per month to keep
exclusive 50% discount on all purchases
renews monthly, pause or cancel renewal anytime

lite $19.99 per month

access to all Manning books, including MEAPs!

team

5, 10 or 20 seats+ for your team - learn more

eBook

$54.99 $27.49

you save $27.50 (50%)

include audio $24.99 $12.49

eBook

pdf, ePub, online

$54.99 $27.49

you save $27.50 (50%)

include audio $24.99 $12.49

pro $24.99 per month

access to all Manning books, MEAPs, liveVideos, liveProjects, and audiobooks!
choose one free eBook per month to keep
exclusive 50% discount on all purchases
renews monthly, pause or cancel renewal anytime

lite $19.99 per month

access to all Manning books, including MEAPs!

team

5, 10 or 20 seats+ for your team - learn more