Package scope rules in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing package-level variables

What is the output of this Go program?

Go

package main

import "fmt"

var packageVar = 10

func main() {
    fmt.Println(packageVar)
}

A Compilation error: packageVar undefined

B 0

C 10

D Runtime panic

💡 Hint

Package-level variables are accessible inside functions within the same package.

The variable packageVar is declared at package level and initialized to 10. It is accessible inside main(), so printing it outputs 10.

❓ Predict Output

intermediate

Accessing unexported variable from another package

Given two packages, main and utils, where utils has an unexported variable, what happens when main tries to access it?

Go

package utils

var secret = 42

package main

import (
    "fmt"
    "utils"
)

func main() {
    fmt.Println(utils.secret)
}

A 0

B 42

C Runtime panic

D Compilation error: secret is not exported by package utils

💡 Hint

In Go, identifiers starting with lowercase letters are unexported and not accessible outside their package.

The variable secret starts with a lowercase letter, so it is unexported and cannot be accessed from main package. This causes a compilation error.

🔧 Debug

advanced

Why does this code fail to compile?

Consider this Go code snippet. Why does it fail to compile?

Go

package main

import "fmt"

func main() {
    fmt.Println(helperVar)
}

var helperVar = 5

A Compilation error: undefined helperVar

B It compiles and prints 5

C Compilation error: helperVar used before declaration

D Runtime panic: nil pointer dereference

💡 Hint

Package-level variables are initialized before main runs, regardless of their position in the file.

In Go, package-level variables are initialized before main() runs, so helperVar is accessible even if declared after main(). The code compiles and prints 5.

❓ Predict Output

advanced

Shadowing package-level variable inside function

What is the output of this Go program?

Go

package main

import "fmt"

var count = 100

func main() {
    count := 50
    fmt.Println(count)
}

A 50

B 100

C Compilation error: count redeclared

D 0

💡 Hint

A variable declared inside a function with := shadows the package-level variable.

Inside main(), count := 50 declares a new local variable count that shadows the package-level count. So printing count outputs 50.

❓ Predict Output

expert

Package variable initialization order with init functions

What is the output of this Go program?

Go

package main

import "fmt"

var x = initializeX()

func initializeX() int {
    fmt.Println("initializeX called")
    return 42
}

func init() {
    fmt.Println("init function called")
}

func main() {
    fmt.Println("main function called")
    fmt.Println(x)
}

A

initializeX called
init function called
main function called
42

B

init function called
initializeX called
main function called
42

C

main function called
initializeX called
init function called
42

D Compilation error

💡 Hint

Package variables are initialized before init functions run.

First, package-level variables are initialized, so initializeX() runs and prints its message. Then init() runs. Finally main() runs. So the output order is initializeX called, init function called, main function called, 42.