Understanding Go Modules, Packages and main Package

Let's break this down in a very simple, real-world way. We'll use a **bakery **as a metaphor to explain Go modules, packages, imports, and the main package.

🍞 Real-World Analogy: A Bakery Shop

🔹 Imagine:

• You're running a bakery shop.
• Your shop has multiple departments: Bread, Cakes, Billing, etc.
• Each department has its own set of tools and recipes (code).
• You also sell your baked goods to customers (this is your main service).

📦 1. What is a Go package?

A package is like a department in your bakery:

• bread → All code to make bread.
• cake → All code to make cakes.
• billing → All code to handle payments.

Each department (package) focuses on a specific job and has its own folder.

// cake/cake.go
package cake

func MakeCake() string {
    return "Chocolate Cake"
}

📁 2. What is a Go module?

A module is your entire bakery business.

It’s a** collection of all departments (packages)** under one roof.

• 1. A Go module is created with go mod init and has a go.mod file.
• 2. It tells Go: “This is where my business (code) starts and who I depend on.”

go mod init github.com/mybakery/shop

This means your bakery's official name is: github.com/mybakery/shop.

🔗 3. What is an import?

An import is when one department wants to use tools from another.

// main.go
package main

import (
    "fmt"
    "github.com/mybakery/shop/cake"
)

func main() {
    fmt.Println("We made:", cake.MakeCake())
}

• Here, the main shop is using the cake department's recipe to make a cake.
• You use import to pull in the code you need from other packages (your own or third-party).

🧠 4. What is the main package, and why is it mandatory?

The main package is the front counter of your bakery.

• This is where customers walk in and interact with your shop.
• In Go, the program starts execution from the main package, specifically the main() function.

// main.go
package main

func main() {
    // Entry point: This is where Go starts running your program
}

If there's no main package, it's like a bakery with no front counter. It has great recipes, but nobody knows how to start using them!

✅ Summary

💡Real Example
You’re building a tool that:

• Has maths functions (addition, subtraction).
• Shows results from the main program.

File: go.mod

module github.com/mytools/calc

File: maths/add.go

package maths

func Add(a, b int) int {
    return a + b
}

File: main.go

package main

import (
    "fmt"
    "github.com/mytools/calc/maths"
)

func main() {
    sum := maths.Add(3, 4)
    fmt.Println("Sum is:", sum)
}