Go

PoC Software Pool 2024 - Day 01 - Go

Welcome to the Software pool 2024! 🚀

During this week, you will learn the base of the modern web programming, core concept of frontend, backend, data storage... with a piece of devops.

Day purposes

✔️ Setup a Go project.

✔️ Learn basics of Go.

✔️ Discover software development good practices.

✔️ Introduce you to design pattern, especially MVC.

✔️ Create an interactive application using your terminal.

Introduction

Requirements

Go is a powerful language with many features and capabilities, you can manage any Go project from its complete CLI.

With it, you can build a go binary, download dependencies, format your code... If you are curious, you can look at the CLI documentation 😉

Start by installing the CLI, you can verify that everything works using the command below:

# Version must be at least 1.16
go version
# go version go1.19.4 linux/amd64

If you have any issue don't hesitate to ask the staff for help 😄

Why Go?

Go is an open source programming language created and maintained by Google.
It solves several problems of the modern software world thanks to its simplicity and incredible standard library. It's also really strong to build microservices and software that required high level of performance.

Go has many usage, you can write powerful cloud & networks, CLI, API or DevOps tools.
Because it's a compiled language, it's really fast, much faster than Javascript for instance 🏃

Here's an exhaustive list of Go killer features:

• Easily solve complex concurrency issues with go routine.
• Strongly statically typed
• Amazing dependency management with go module
• Multi-paradigm from OOP to functional

Warp up

Let's begin this pool with a simple warm up: The Go Tour
This tour is a set of exercise to learn Go basics.

You can also try the Go Playground, a useful tool to test or share pieces of codes.

You will also need a good IDE, we recommend Visual Studio Code or GoLand.

In summary, here's a bunch of links that will be very useful during the pool:

• Go Docs
• Go Playground
• Go Tour
• Visual Studio Code Go plugin
• GoLand
• Standard Library

Step 0 - Setup

📑 Description:

As usual, every exercise must be pushed to a git repository.

To make it easier, we will use a GitHub classroom! Follow this link to create your git repository.

📌 Tasks:

Then, you can clone your repository.

git clone [email protected]:PoC-Community/software-pool-days-{YOUR-GITHUB-USERNAME}.git

For each day, we will create a new folder. Start with the day01.

mkdir -p day01

Inside it, let's initialize a Go project

go mod init SoftwareGoDay1
> go: creating new go.mod: module SoftwareGoDay1

You should see a go.mod file appear in your directory.

You can now create your first go file: main.go 🎉

package main

import "fmt"

func main() {
  fmt.Println("You are ready to start the 2024 PoC software pool!")
}

📚 Documentation:

💡 If you are curious about this, check the fmt package documentation

✔️ Validation:

Let's execute it:

# Use `go run` to execute your program without building the binary
go run SoftwareGoDay1 # Or go run ./main.go

# You can also build and run it in separate command
go build SoftwareGoDay1
./SoftwareGoDay1

# You should have the following output
> You are ready to start the 2024 PoC software pool!

Before going further, do the Go Tour and read the package documentation, those core concepts are important to understand the rest of the pool 💯

Step 1 - Hello World

📑 Description:

It's time to start coding! We will start with a simple helloWorld package.

📌 Tasks:

Let's create a folder helloWorld with a file helloWorld.go in it.

mkdir -p helloWorld

You will implement a function HelloWorld that will display Hello World! in your terminal.

Don't forget to add the correct package name at the top of helloWorld.go 😉

Update the file main.go to call HelloWorld.

📚 Documentation:

💡 Here's a couple of slides about what is a good naming in Go.

✔️ Validation:

go run SoftwareGoDay1

# You should have the following output
> Hello world!

Step 2 - Loops, conditions, array and unit tests

📑 Description:

The purpose of this step is to use what you have learned during the Go Tour 👀

Let's create a function to sort numbers, so we can cover useful concepts such as loops, conditions, arrays and tests 🥳

📌 Tasks:

Your function must:

1. Sort a list in ascending order
2. Remove odd numbers
3. Format the result to return

Sort like a pro

Create a new package getEvenNumbers with a file getEvenNumbers.go.

mkdir -p getEvenNumbers

Create a function GetEvenNumbers that will take an array of int.
It must sort the array in ascending order and return a string that contains only pairs number in ascending order, split by a -.

Update main.go to call GetEvenNumbers and display the result:

array := []int{
  	1,
  	0,
  	19,
  	17,
  	16,
  	8,
  	13,
  	24,
  }

fmt.PrintLn(getEvenNumbers.GetEvenNumbers(array))

✔️ Validation:

You should have the following result:

0 - 8 - 16 - 24

Test like a pro 🧪

📑 Description:

It's really important to correctly test your code, a code not tested can lead to unpredictable bugs and the time lost to debug it could be avoided by creating some tests.

📚 Documentation:

To do so, Go provides a built-in test package, with a clean way to organize your tests 💥

Let's create a test file named getEvenNumbers_test.go.

📌 Tasks:

To make sure your getSortedEvenNumbers works as intended, you can write a test for each of these cases:

• Only positive numbers
• Only negative numbers
• Mixed numbers

✔️ Validation:

You can then execute them with go test, which should produce a result similar to this one:

go test ./getEvenNumbers -v

=== RUN   TestGetEvenNumbersCasePositive
--- PASS: TestGetEvenNumbersCasePositive (0.00s)
=== RUN   TestGetEvenNumbersCaseNegative
--- PASS: TestGetEvenNumbersCaseNegative (0.00s)
=== RUN   TestGetEvenNumbersCasePositiveAndNegative
--- PASS: TestGetEvenNumbersCasePositiveAndNegative (0.00s)
PASS
ok      SoftwareGoDay1/getEvenNumbers     0.001s

Step 3 - My name is ...

📑 Description:

Now it's time to learn how to read input from the terminal 🤩

📌 Tasks:

Create a new package whatIsYourName with a file whatIsYourName.go and a function WhatIsYourName inside it.

mkdir -p whatIsYourName

This function must display a prompt in the terminal to ask a user to fill his name and retrieve it.

📚 Documentation:

To do so, you can use the bufio and os packages 😉

✔️ Validation:

You should end up with the following behavior:

What is your name ?
# User fill input
> Slim Shady

# Display input
Your name is Slim Shady

Don't forget to call it from main.go and correctly manage errors.

💡 Display your errors using the log package and fmt.Errorf.

Testing time

📑 Description:

It's really hard to test I/O with unit test, but that's why functional tests exist!

📚 Documentation:

Download them from GitHub and extract sources in your directory 📁

📌 Tasks:

Then, create a binary of your project using go build.

✔️ Validation:

You can now simply execute testWhatIsYourName to launch the tests of your function:

OK - TEST 1 PASSED
OK - TEST 2 PASSED
OK - TEST 3 PASSED

Don't hesitate to add more tests and modify your program to make sure all of them pass 🧪

Step 4 - Make it the cutest code that I have ever seen

📑 Description:

As we said in the introduction, Go come with great built-ins to help you during your development.

📚 Documentation:

One of these tools is gofmt, a powerful formatting tool that will help you have standard coding style rules in your code.

Its really helpful on the format, but having a clean code architecture is up to you 🚀

📌 Tasks:

To use gofmt, just launch go fmt . at the root of your module 😉

You can also configure VSCode or GoLand to format your code on save.

Step 5 - Artists Book v1.0

📚 Documentation:

You are ready for a complex exercise. Let's create our first application!

It will be a program that help you manage your favorite artists from your terminal.

We will not code everything in one step, that would be too huge for this moment.

⚠️ Read the whole step before coding, it will help you understand what to do and how to do it

📌 Tasks:

Let's start with a simple implementation. The goal is to have a CLI similar to this one:

Welcome into your Artists Book!

What do you want to do?
1 - List my favorite artists
2 - Leave

# User tip input
> 3

Tip 1 or 2.

# User tip input
> 1

Here's your favorite artists:
-- 1 -- B2O
-- 2 -- SCH
-- 3 -- Laylow
-- 4 -- Billie Eilish

What do you want to do?
1 - List my favorite artists
2 - Leave

# User tip input
> 2

See you!

📚 Documentation:

To do this, we must build a program that follows a strong architecture. We will use one of the most popular: MVC.

MVC stands for Model - View - Controller. It's an architecture where your code logic is split into smaller parts to easily maintain and scale a project.

We will now adapt MVC to our need, don't worry if we do not strictly follow the architecture.

Here's a schema of your architecture:

📌 Tasks:

Let's code step by step 😄

Router

Router corresponds to the entrypoint of your program and the main loop.
It has different roles:

• Display actions to user.
• Catch the user input.
• Call controllers to execute the action asked by the user.

A good architecture also requires a good folder management in your code. Each resource must be in its own package and with the router making the link between them.

• Create a package artistsBook with a file router.go in it.
• Create a function Router that will do the loop described in the example.

You are big boy/girl now, you got the keys to do it by yourself 💪

• Update main.go to call Router.

Controllers

A controller is in charge of the business logic that manages your resources.

Its only purpose is to create the link between the function that manage your data storage (for now it will be a simple JSON file) and functions exposed to the user.

• Create a package controllers in artistsBook folder.
• Create a sub-package artists in it.
• Create a file display.go
• Write the function DisplayAll that controls the display of the user's favorite artists

Repositories

A repository is responsible for all interactions with the data storage.

• Create a package repositories in the artistsBook folder.
• Create a sub-package artists in it.
• Create a file get.go
• Write the function GetAll that retrieves user's favorite artists

📚 Documentation:

You will need the os and json packages to read a file (see more information below).

Views

A view expose a list of functions to the user to make it interact with a resource.

• Create a package views in artistsBook folder.
• Create a sub-package artists in it.
• Create a file display.go
• Write the function DisplayAll that display the user's favorite artists in the terminal.

Models

A model defines the type of the stored data.

• Create a package models in artistsBook folder.
• Create a sub-package artist
• Create a file artist.go in it
• Export a struct Artist that contains a field name of type string

Data

Data defines your storage, it can be a database, an Excel file or whatever that can store data. Here, it will be a simple JSON file.

📚 Documentation:

JSON stands for JavaScript Object Notation. It's a standard like CSV, XML or YAML used to define a structured data.

We'll discover real databases tomorrow 👀

• Create a directory data in the artistsBook folder.
• Create the file artists.json with the following content :

[
  {
    "name": "B2O"
  },
  {
    "name": "SCH"
  },
  {
    "name": "Laylow"
  },
  {
    "name": "Billie Eilish"
  }
]

✔️ Validation:

Summary

Finally, you should have the following architecture:

artistsBook/
  router.go
  controllers/
    artists/
       display.go
  repositories/
    artists/
      get.go
  views/
    artists/
       display.go
  models/
    artist.go
  data/
    artists.json

This exercise may seems hard but if you write your code step by step, it will be a piece of cake 🍰!

Step 6 - Artists Book v2.0

📑 Description:

You've built the base of your MVC architecture, it's time to improve it 📈

For now, you can only read data, let's add operations to create, update or delete it.

Those four primitive operations are mandatory to manage a resource in a data storage.

📚 Documentation:

They are usually called CRUD, which stands for CREATE - READ - UPDATE - DELETE.

📌 Tasks:

Let's add the missing ones 🚀

CREATE

Update your codebase to allow a user to add a new artist to his list.

Repository

Add a file create.go in your artists repository that will contain the function Create to add an artist to the database.

⚠️ You will need to write the whole artists.json file
Take care to not lose data when you rewrite the file.

View

• Create the file ask.go in the views/artists directory.
• Write the function AskName that retrieve an artist's name from the terminal.

💡 You can copy code from the precedent step to win time

Controller

• Create the file create.go in controllers/artists directory.
• Write the function Create that controls the artist addition.

Routing

Add the possibility to create an artist in router.go.

Result

You can code other functions to make your code works. For example, a function to display the artist name if it has been correctly added to the list.
This function should be in the views, in display.go for example.

✔️ Validation:

You should have the following result:

Welcome into your Artists Book!

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Leave

# User tip input
> 2

What's the artist's name?

# User tip input
> Bob Marley

Bob Marley has been added to your favorite artists!

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Leave

# User tip input
> 1

Here's your favorite artists:
-- 1 -- B2O
-- 2 -- SCH
-- 3 -- Laylow
-- 4 -- Billie Eilish
-- 5 -- Bob Marley

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Leave

# User tip input
> 2

What's the artist's name?

# User tip input
> Bob Marley

Bob Marley already exists!

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Leave

# User tip input
> 3

See you!

UPDATE

Update your application to allow the user to update an artist in his list.

Repository

Create the file update.go in your repository/artists folder.

Add the function Update to modify an artist in the data storage.

View

Add the function AskNewName in your views/artists directory.

I'm sure you have understood the logic 🧠

Result

Don't forget to update your controller, the router and add anything required to correctly update an artist.

✔️ Validation:

You should have a result similar to this one:

Welcome into your Artists Book!

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Leave

# User tip input
> 2

What's the artist's name?

# User tip input
> Bob Marley

Bob Marley has been added to your favorite artists!

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Update an artist in my favorite
4 - Leave

# User tip input
> 3

What's the name of the artist you want to update?

# User tip input
> unknown

What will be the new name of unknown?

# User tip input
> Mac Miller

unknown is not in your favorite list.

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Update an artist in my favorite
4 - Leave

# User tip input
> 3

What's the name of the artist you want to update?

# User tip input
> B20

What will be the new name of unknown?

# User tip input
> Booba

B2O has been successfully updated.

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Update an artist in my favorite
4 - Leave

# User tip input
> 1

Here's your favorite artists:
-- 1 -- Booba
-- 2 -- SCH
-- 3 -- Laylow
-- 4 -- Billie Eilish
-- 5 -- Bob Marley

What do you want to do?
1 - List my favorite artists
2 - Add an artist to my favorite
3 - Update an artist in my favorite
4 - Leave

# User tip input
> 4

See you!

DELETE

Update your codebase to allow user to remove an artist from his list.

It's up to you to find the best way to do it 🚀

Step 7 - Artists Book v3.0

📑 Description:

You have implemented a complete MVC architecture, that's excellent 🚀

Only one thing is missing, our data is too basic, it only has a name.

📌 Tasks:

Let's add some fields by updating the Artist structure:

• id: A unique identifier of type string
• top: Best song, as a string
• fans: number of fans
• listenedTime: the amount of time you listened to this artist. It must be stored as a Time

💡 It's common to put a unique identifier when you store data, this way, you can easily distinguish them.

You'll have to update all your codebase to support those new fields.

Don't worry, it's not that hard because you have build a strong architecture!
And if you struggle, remember that the staff is here to help you out 😃

Step 8 - Interface

📑 Description:

It's time to learn another important concept in Go: interfaces.

To do so, we will do a simple example with geometric shapes 🟥

📌 Tasks:

Let's create a package geometricShape.

mkdir -p geometricShape

Definition

Inside it, create an interface GeometricShape with a method CalcPerimeter.
This method must have the following prototype:

CalcPerimeter() float64

Create a function CalcPerimeter that will take this time an interface GeometricShape as parameter and return the result of the function CalcPerimeter called from the interface.

Here's a prototype to help you:

func CalcPerimeter(shape GeometricShape) float64

Shapes

Create the struct Circle with a field Radius.
Create the struct Rectangle with a field X and Y.
Create the struct Triangle with a field X, Y and Z.

For each shape, implement the method CalcPerimeter that will return the parameter of the shape.

Here's an example of prototype for a Square:

func (square Square) CalcPerimeter() float64 {}

💡 As you may have noticed, you can write a Go function in this order too (parameters before the function name)

Upgrade

Update the file main.go to create 3 shapes:

• A Circle with radius: 12.0
• A Rectangle with X: 2.0 and Y: 3.0
• A Triangle with X: 5.0, Y: 2.0 and Z: 1.0

For each shape, display their perimeter using CalcPerimeter from the package geometricShape.

Here's an example of output:

&{12} has a perimeter of 75.398224
&{2 3} has a perimeter of 10.000000
&{5 2 1} has a perimeter of 8.000000

As you can see, it's not clear... Let's use the power of interfaces to fix that 😃

📚 Documentation:

The package fmt call the method String of given the given argument to display it properly.

So if our structures implement the method String, you can control the way it's displayed by fmt 😉

Update your structures to print it correctly, here's an example of prototype with Square:

func (square Square) String() string {}

Thanks to interfaces, you do not have to change anything in main.go, just rerun the program and appreciate the moment 😍

✔️ Validation:

# You can configure `String()` to display this
Circle: { radius = 12 } has a perimeter of 75.398224
Rectangle: { X = 2, Y = 3 } has a perimeter of 10.000000
Triangle: { X = 5, Y = 2, Z = 1 } has a perimeter of 8.000000

Step 9 - Artists Book v4.0

📑 Description:

Since you now know interfaces why not use it in your MVC?

📌 Tasks:

The purpose is to update Artist to correctly display it with fmt package.

In your artist model, implement the method String.

You can also update DisplayAll from your views to use a simple fmt.Printf to display Artist.

Bonus

First, congratulation! You've survived day 1 👏

Your MVC currently manages only one resource: Artist.

You can create a new resources named Music containing the following data:

• id: Resource unique identifier
• artist: Owner of the music
• name: Music's title
• listened: Number of listening
• link: A link to the music (E.g: spotify, youtube...)

You're free to add any features to your application.

You can maybe start by adding the CRUD for your new Music resource.

📚 Documentation:

Additional resources

• Clean code in Go
• Go benchmark
• Go amazing project
• Generics
• Go routines
• Courses

Organization

🚀 Don't hesitate to follow us on our different networks, and put a star 🌟 on PoC's repositories.