Introduction

Hey there! Welcome to Part 2 of the series of Learning Go with me. In Part 1 we set the stage by introducing the project, defining its goals, and setting up the basic folder structure for our Go project.
Now it’s time to dive deeper into some fundamental concepts of Go programming.
In this part, we’ll cover core topics like how Go organizes code using packages and imports, how exported names work, and explore basic Go constructs such as types, variables, constants, functions, slices, maps, loops, and conditionals. Then we’ll also understand how structs and pointers work.
I will try my best to explain each concept in a beginner-friendly way and in a way that I understand because I am also learning with you. I will try to incorporate these concepts in a way that after understanding it we can directly apply it to our CRUD API project.
By the end of this section, you’ll have a strong grasp of these concepts and be ready to use them to bring our API to life.
Let’s jump right in it without wasting any more time

Packages

What is a Package in Go?

In Go, packages are a way to organize and reuse code. What does that mean?
Think of a Package like a Folder on your computer. Inside that folder, you have related files. Similarly in Go, the files inside a package folder work together to provide some functionality
For example:
- If you are familiar with math package in any other language then you must know that it contains tons of mathematical operations. So all these operations are inside this math package
And when you want these functions which are defined somewhere else inside your program, you use “import“.

Types of Packages

Standard Library Packages:
- These are built-in packages in Go. Packages like math for mathematical operations, net/http for handling HTTP requests, encoding/json for working with JSON, etc.
Third-Party Packages:
- These are the additional packages that are created by people in the Go community. If you remember, in Part 1 we installed a few dependencies using go get the command. Those belong to this type.
Custom Packages:
- You can create your own packages too which you can use to organize code. We will see this in action soon.

How Packages Work?

In Go, every program belongs to a package. The main package is special because it’s where the program starts running. When we define the main package inside a file, Go will know from where it should start the program.

Using Packages in Our Project

In Part 1 we created different folders and files. If you have noticed, every folder and files are in red color which shows that something is wrong. This is because we need to tell which file belongs to which package. Let’s resolve this.

Go to each file and write the folder name as a package it belongs to.

// cmd/main.go
package main

// config/config.go
package config

// databse/db.go
package database

// internal/books/handler.go, model.go and service.go
package books

// routes/routes.go
package routes

//pkg/logger
package logger

All the errors should be gone after giving the package name inside every file.

Imports

To use any package inside a Go project, we need to import it using import a keyword.

import "fmt"

If you have multiple packages then list them in parentheses

import (
    "fmt"    // for printing.
    "net/http"    // to handle HTTP requests and responses.    
    "encoding/json"    // to parse and generate JSON data
)

Exported Names

What Are Exported Names?

So in Go, we don’t have keywords like private or public like other languages.
If the name starts with an uppercase letter, then it is considered as exported, meaning it can be accessed from outside the package where they’re defined.
Names starting with a lowercase letter are unexpected and private to the package.

Example

type Book struct {    // Exported struct
    Title string    // Exported field
    Author string    // Exported field
}

type car struct {    // Unexported struct
    brand string    // Unexported field
    isElectric bool    // Unexported field
}

Above we created two structs (don’t worry if you don’t know about structs. We will see it in detail in this blog below).
Here Book starts with an uppercase letter, meaning we can get this struct in other packages whereas car starts with a lowercase letter, meaning we can’t access this struct anywhere else.

Basic Go Concepts

Types and Variables

Go is a statically typed language. This means every variable must have a type that’s known at compile time. Common types include:
- int: Integer values
- string: Text data
- bool: Boolean values (true/false)
- float: Decimal values

Declaring Variables

There are two ways you can declare a variable:

Explicit Declaration

var age int = 24
var name string = "Dhruv"

Implicit Declaration

age := 24
name := "Dhruv"

You can also declare with no value like this:

var age int    // Defaut: 0
var name string    // Default: ""

Constants

Constants are immutable values, which means we can’t change them once defined.
Use const keyword to declare constants
Why Use Constants?
- We use it to prevent accidental changes to critical values.
- To improve the readability and maintainability of code

const apiVersion = "v1"
const defaultPort = 8080

You can use parentheses for multiple declarations too

const (
    apiVersion = "v1"
    defaultPort = 8080
)

Functions

We use func keyword to declare functions in Go.

func functionName(){
    // logic
}

You can have parameters inside parentheses

func functionName(parameter1 type, parameter2 type){
    // logic
}

You can return from a function by defining a return type like this

// Single value return
func functionName() int {
    return 0   
}

// For multiple value return
func functionName() int, string {
    return 0, "Hello"
}

Conditionals

The if statement is used for decision-making

marks := 85
if marks >= 9- {
    fmt.Println("Grade: A")
} else if marks >= 75 {
    fmt.Println("Grade: B")
} else {
    fmt.Println("Grade: F")
}

Short Statement with if. In this, we are first declaring num , and right after that we are checking the condition for it.

if num := 10; num%2 == 0 {
    fmt.Println("The number is even.")
} else {
    fmt.Println("The number is odd.")
}

Loops

In Go we have only for loop for looping. There are different ways you can use for loop. Let’s see it in action

// Basic `for` loop
for i:= 0; i<5; i++ {
    fmt.Println("Value of i: ,", i)
}

// Infinite Loop
count := 0
for {
    fmt.Println("Looping forever")
    count++
    if count == 3 {
        break // Exists the loop
    }
}

// Condition Only Loop
count:= 0
for count < 3 {
    fmt.Println("Count: ", count)
    count++
}

Struct

If you come from programming languages like Javascript, Dart, or Python, you must be familiar with class and objects.
In Go we don’t have that. We use struct to group data together.
Let’s take an example of our CRUD API project. We need to represent a book with multiple details like a title, id, name, etc.
So instead of creating separate variables for each piece of data, you can use a struct to combine all of those into one entity.

Defining a Struct

To define a structure, you use the type keyword followed by the structure name and its field. Each field has a name and a type

type Book struct {
    ID string
    Title string
    Author string
    Year int
}

Creating and Using a Struct

Once we have defined a structure, we can use it to create an object and assign values to its fields

var book1 Book    // Creates an instance of `Book` struct
book1.ID = "1"    // Assigns the value "1" to the ID field of struct
book1.Title = "Maths"
book1.Author = "Jane"
book1.Year = 2012

Initializing a Struct in Different Ways

Using Field Names
- We can initialize a struct by specifying the field names and their values like below

    book1 := Book{
        ID: "1"
        Title: "Maths"
        Author: "Jane"
        Year: 2012
    }

This looks clear, isn’t it?

Without Field Names
- We can initialize it without field names too like this

    book1 := Book{
         "1"
         "Maths"
         "Jane"
         2012
    }

This is less readable because it relies on the order of fields.

Structs with Methods

A method is a function that is attached to a specific type. This type of method initialization was new and kinda weird for me at first. Because usually we are required to create methods inside a class in other languages right? but here we create it separately and then attach it to the structure using the receiver.
Let me show you how

type Book struct {
    ID string
    Title string
    Author string
    Year int
}

func (b Book) SayBookName() {
    fmt.Println("This book name is: ", b.Title)
}

func main() {
    book1 := Book{
        ID: "1"
        Title: "Maths"
        Author: "Jane"
        Year: 2012
    }

    book1.SayBookName() // Call the SayBookName method
}

As you can see to attach this SayBookName method to Book struct we provided receiver before the method name inside the parenthesis (b Book). So Inside this file wherever any method has this receiver it will automatically get attached to this struct.
You can also nest struct inside a struct like this

type Book struct {
    ID string
    Title string
    Author Author // Nested struct
    Year int
}

type Author struct {
    FirstName string
    LastName string
}

func main() {
     book1 := Book{
        ID: "1"
        Title: "Maths"
        Author: Author{
            FirstName: "Jane"
            LastName: "Doe"
        }
        Year: 2012
    }
}

Slice

A slice in Go is a data structure used to hold a collection of elements of the same type.
Think of it as a more powerful and flexible version of an array.
While arrays have fixed sizes, slices can grow and shrink dynamically.
It’s really simple to use

Creating Slices

Using the make function
- The make function creates a slice with a specific length and capacity.

slice := make([]int, 3, 5) // Create a slice of type int, of length 3 and capacity 5

Here length represents the number of elements currently in the slice which is 3 here: [0,0,0]
And Capacity represents the total space allocated for the slice which is (5). This means this slice can have max 5 elements in it.

Using a Slice Literal
- We can define a slice directly with values using slice literal

slice := []int{1,2,3,4,5}

Adding Elements to a Slice

We can add elements to a any slice using append function.

slice := []int{1,2,3}
slice = append(slice, 4,5) // adding 4 and 5 to the slice

We need to pass the slice where we want to add elements as the first parameter and then we can pass as many elements as we want after that.

Iterating Over a Slice

We use for loop to access elements in a slice

slice := []int[1,2,3,4,5]

for index, value := range slice {
    fmt.Println("Index: ", index, "Value: ",value)
}

for _, value := range slice {
    fmt.Println("Value: ",value)
}

Range

Here range the keyword is used to iterate over elements in a variety of data structures. In the above example, we use range to print the index and value in a slice.
We use underscore (_) to skip the variable if it’s not needed

Slicing a Slice

We can create a new slice by slicing an existing one.

slice := []int{1,2,3,4,5}
newSlice := slice[1:3] // Slice from index 1 to 2 (3 is exclusive)

// newSlice: [2,3]

Length And Capacity

Slices have both length and capacity as we saw above. To get the length and capacity of a slice we use len() and cap() functions

slice := []int{1,2,3,4,5}
fmt.Println("Length: ", len(slice)) // 5
fmt.Println("Capacity: ", cap(slice)) // 5

Appending Slices

We can add a whole new slice to an existing slice using . . . (unpack operator)

  slice := []int{1,2,3,4,5}
  slice2 := []int {6,7,8}

  combined := append(slice, slice2...) // [1,2,3,4,5,6,7,8]

Map

This is another very helpful data structure in Go which is built in inside it. It stores key , value . This is similar to dictionaries in Python or hash maps in other programming languages.
Keys must be of a comparable type that is string, int and values can be of any type.
This data structure is useful, especially for lookups when the key uniquely identifies the data. In our case, it is Book ID

Declaring and Initializing a Map

Using make

myMap := make(map[string]int)

myMap["Maths"] = 2
myMap["Biology"] = 3

Here [string] represents key and int represents value

Using Map Literal
- We can initialize and create a map in a single step like we did in struct

myMap := map[string]int{
    "Math": 2,
    "Biology": 3,
}

Accessing Values in a Map

To get the value associated with a key, you have to use the map followed by the key in square brackets

myMap := map[string]int{
    "Math": 2,
    "Biology": 3,
}

fmt.Println(myMap["Maths"]) // 2

Checking if a Key Exists

We use the comma ok idiom to check if a key exists or not. This is very useful when we need to check if certain keys exist in a map or not. We can do that in a single line of code

myMap := map[string]int{
    "Math": 2,
    "Biology": 3,
}

value, ok := myMap["Physics"]

if exists {
    fmt.Println("Value: ", value)
} else {
    fmt.Println("Key does not exist")
}

value, exists := myMap["Physics"]: ok is true if the key is present and false otherwise.

Adding and Updating Elements

It’s really easy, you just access the value using the key and add a new value or assign a different value to it

myMap := map[string]int{
    "Math": 2,
    "Biology": 3,
}

myMap["Physics"] = 4 // Adding new element

myMap["Math"] = 1 // Updating exisitng element

Deleting Elements

We use delete() function to remove a key-value pair from the map

myMap := map[string]int{
    "Math": 2,
    "Biology": 3,
}

delete(myMap, "Math") // Remove the key "Math"

Iterating Over a Map

We use again for loop with range to iterate over all key-value pairs.

myMap := map[string]int{
    "Math": 2,
    "Biology": 3,
}

for key, value:= range myMap {
    fmt.Println("Key: ", key, "Value: ", value)
}

Wrapping Up

I think that’s pretty much all you need to know for now. We learned lots of fundamental stuff in this article. I tried to make it as concise as possible in order to quickly grasp the underlying concepts because going into too much detail with all the theory doesn’t make sense at this point.
There is still one concept remaining which is Pointers. I wanted to cover it in this blog only but then thought it would become quite a big read so I will be explaining it in detail in the next blog.
I hope after this article you are at least comfortable with the basic stuff and syntaxes. Just practice the syntax that you find difficult to grasp. It will all make sense and your hands will then flow naturally on the keyboard afterwards.
See you in the next one, until then…

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From Zero to Go Hero: Learn Go Programming with Me - Part 1

More from this blog

Introduction

Packages

What is a Package in Go?

Types of Packages

How Packages Work?

Using Packages in Our Project

Imports

Exported Names

What Are Exported Names?

Example

Basic Go Concepts

Types and Variables

Declaring Variables

Constants

Functions

Conditionals

Loops

Struct

Defining a Struct

Creating and Using a Struct

Initializing a Struct in Different Ways

Structs with Methods

Slice

Creating Slices

Adding Elements to a Slice

Iterating Over a Slice

Range

Slicing a Slice

Length And Capacity

Appending Slices

Map

Declaring and Initializing a Map

Accessing Values in a Map

Checking if a Key Exists

Adding and Updating Elements

Deleting Elements

Iterating Over a Map

Wrapping Up