Zero Values & Defaults

Part of the Object Oriented Programming section of Coddy's GO journey — lesson 17 of 107.

In Go, every variable has a zero value — the default value assigned when you declare a variable without explicit initialization. Understanding zero values is essential for working with structs, as uninitialized fields automatically receive these defaults.

Each type has its own zero value:

Type	Zero Value
int, float64	`0`
string	`""` (empty string)
bool	`false`
pointer, slice, map	`nil`

When you create a struct, any field you don't explicitly set gets its zero value.

type User struct {
    Name   string
    Age    int
    Active bool
}

func main() {
    var u User
    fmt.Println(u.Name)   // "" (empty string)
    fmt.Println(u.Age)    // 0
    fmt.Println(u.Active) // false
}

This also applies to partial initialization. Only the fields you specify get custom values.

u := User{Name: "Alice"}
fmt.Println(u.Age)    // 0
fmt.Println(u.Active) // false

Zero values make structs immediately usable without explicit initialization. However, be careful with reference types like slices and maps — their zero value is nil, which can cause runtime panics if you try to use them without initialization.

Challenge

Easy

Let's build a player profile system that demonstrates how zero values work in Go. You'll create a game profile where some fields are explicitly set while others rely on their default zero values.

You'll organize your code across two files:

player.go: Define a Player struct with the following fields: Username (string), Level (int), Score (int), IsPremium (bool), and GuildName (string). Also create a DisplayProfile method that returns a formatted string showing all the player's information.
main.go: Read a username from input and create a Player using only partial initialization—set just the Username field. Then display the complete profile to see how Go fills in the unset fields with their zero values.

The following input will be provided:

Line 1: The player's username

Your DisplayProfile method should return a string in this exact format:

Username: [Username]
Level: [Level]
Score: [Score]
Premium: [IsPremium]
Guild: [GuildName]

For example, if the username is ShadowKnight, your output should show the username along with all the zero values for the uninitialized fields:

Username: ShadowKnight
Level: 0
Score: 0
Premium: false
Guild:

Notice how the Guild field shows nothing after the colon—that's the empty string zero value. This challenge helps you see exactly what Go assigns to each type when you don't provide an explicit value.

Cheat sheet

In Go, every variable has a zero value — the default value assigned when you declare a variable without explicit initialization.

Each type has its own zero value:

Type	Zero Value
int, float64	`0`
string	`""` (empty string)
bool	`false`
pointer, slice, map	`nil`

When you create a struct, any field you don't explicitly set gets its zero value:

type User struct {
    Name   string
    Age    int
    Active bool
}

func main() {
    var u User
    fmt.Println(u.Name)   // "" (empty string)
    fmt.Println(u.Age)    // 0
    fmt.Println(u.Active) // false
}

Partial initialization — only specified fields get custom values:

u := User{Name: "Alice"}
fmt.Println(u.Age)    // 0
fmt.Println(u.Active) // false

Zero values make structs immediately usable without explicit initialization. Be careful with reference types like slices and maps — their zero value is nil, which can cause runtime panics if used without initialization.

Try it yourself

package main

import (
	"fmt"
)

func main() {
	// Read the username from input
	var username string
	fmt.Scanln(&username)

	// TODO: Create a Player using partial initialization
	// Only set the Username field, let other fields use zero values

	// TODO: Display the player's profile using the DisplayProfile method
}