Module initialization in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the module path in the go.mod file.

Go

module [1]

Drag options to blanks, or click blank then click option'

Agithub.com/user/project

Bpackage main

Cimport fmt

Dfunc main()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'package main' instead of the module path.

Writing 'import fmt' in the module declaration.

Putting function code in go.mod file.

The module keyword is followed by the module path, like github.com/user/project.

2fill in blank

medium

Complete the code to initialize a new Go module using the command line.

Go

go [1] github.com/user/project

Drag options to blanks, or click blank then click option'

Abuild

Brun

Cmod init

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'go build' instead of 'go mod init'.

Using 'go get' which is for fetching packages.

Typing 'go run' which runs Go programs.

The command go mod init initializes a new module with the given path.

3fill in blank

hard

Fix the error in the go.mod file by completing the missing keyword.

Go

[1] github.com/user/project

go 1.20

Drag options to blanks, or click blank then click option'

Apackage

Bmodule

Cimport

Dfunc

Attempts:

3 left

💡 Hint

Common Mistakes

Writing 'package' instead of 'module' in go.mod.

Using 'import' or 'func' which are Go code keywords, not module keywords.

The go.mod file must start with the module keyword followed by the module path.

4fill in blank

hard

Fill both blanks to complete the go.mod file with module path and Go version.

Go

[1] github.com/example/app

go [2]

Drag options to blanks, or click blank then click option'

Amodule

B1.20

C1.18

Dpackage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'package' instead of 'module'.

Putting an invalid Go version like 'package' or 'module' in the version line.

The go.mod file starts with module and specifies the Go version like 1.20.

5fill in blank

hard

Fill all three blanks to create a minimal go.mod file with module path, Go version, and a require statement.

Go

[1] github.com/my/module

go [2]

require [3] v1.2.3

Drag options to blanks, or click blank then click option'

Amodule

B1.20

Cgithub.com/some/dependency

Dpackage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'package' instead of 'module' for the first blank.

Putting an invalid Go version in the second blank.

Leaving the require dependency blank or using an invalid path.

The go.mod file starts with module, specifies the Go version, and lists dependencies with require.

Practice

1. What is the main purpose of the init function in a Go module?

easy

A. To run setup code automatically before main starts

B. To define the main entry point of the program

C. To declare global variables

D. To handle user input during runtime

Solution

1. Step 1: Understand the role of init in Go

   The init function is designed to run automatically before the main function starts.

2. Step 2: Differentiate from other functions

   Unlike main, init is used for setup tasks, not for program entry or input handling.

3. Final Answer:

   To run setup code automatically before main starts -> Option A

4. Quick Check:

   init runs before main [OK]

Hint: Remember: init runs before main automatically [OK]

Common Mistakes:

• Confusing init with main
• Thinking init handles user input
• Assuming init must be called manually

2. Which of the following is the correct syntax to declare an init function in Go?

easy

A. init func() {}

B. func init() {}

C. function init() {}

D. func Init() {}

Solution

1. Step 1: Recall Go function syntax

   In Go, functions start with the keyword func, followed by the function name and parentheses.

2. Step 2: Check init function naming rules

   The init function must be lowercase and have no parameters or return values.

3. Final Answer:

   func init() {} -> Option B

4. Quick Check:

   Correct init syntax = func init() {} [OK]

Hint: Use lowercase init with empty parentheses [OK]

Common Mistakes:

• Capitalizing Init instead of init
• Using wrong keywords like function
• Adding parameters or return types to init

3. What will be the output of this Go program?

package main
import "fmt"
func init() {
    fmt.Println("Init 1")
}
func init() {
    fmt.Println("Init 2")
}
func main() {
    fmt.Println("Main")
}

medium

A. Init 2
Init 1
Main

B. Main
Init 1
Init 2

C. Init 1
Init 2
Main

D. Init 1
Main
Init 2

Solution

1. Step 1: Understand multiple init functions execution order

   All init functions run automatically before main, in the order they appear in the source file.

2. Step 2: Trace the output sequence

   First, "Init 1" prints, then "Init 2", and finally "Main" from the main function.

3. Final Answer:

   Init 1 Init 2 Main -> Option C

4. Quick Check:

   Multiple init run in order before main [OK]

Hint: Multiple init run top to bottom before main [OK]

Common Mistakes:

• Assuming main runs before init
• Thinking init functions run in random order
• Confusing output order of init functions

4. Identify the error in this Go code snippet related to init function:

package main
func init() {
    fmt.Println("Starting")
}
func main() {
    fmt.Println("Running")
}

medium

A. main function must be named Main

B. init function cannot print output

C. Multiple init functions are required

D. Missing import of the fmt package

Solution

1. Step 1: Check for required imports

   The code uses fmt.Println but does not import the fmt package, causing a compile error.

2. Step 2: Validate other code parts

   init can print output, multiple init are optional, and main must be lowercase.

3. Final Answer:

   Missing import of the fmt package -> Option D

4. Quick Check:

   Use import "fmt" to fix [OK]

Hint: Always import packages before using their functions [OK]

Common Mistakes:

• Forgetting to import fmt
• Thinking init cannot print
• Misnaming main function

5. You want to initialize a configuration map before your Go program runs. Which approach correctly uses init to do this?

var config map[string]string

func init() {
    // What should go here?
}

hard

A. config = make(map[string]string)
config["env"] = "production"

B. config := map[string]string{"env": "production"}

C. var config = map[string]string{"env": "production"}

D. config = nil

Solution

1. Step 1: Understand map initialization in init

   The global config variable must be assigned a new map using make before adding keys.

2. Step 2: Check each option

   config = make(map[string]string) config["env"] = "production" correctly initializes and sets a key. config := map[string]string{"env": "production"} uses := which creates a new local variable, not affecting the global. var config = map[string]string{"env": "production"} declares a local config inside init, not affecting the global. config = nil sets config to nil, which is not useful.

3. Final Answer:

   config = make(map[string]string) config["env"] = "production" -> Option A

4. Quick Check:

   Use make to initialize maps before use [OK]

Hint: Use make to initialize maps before adding keys [OK]

Common Mistakes:

• Using := inside init creates local variable
• Not initializing map before assignment
• Setting map to nil instead of a new map