Implementing the init Function in Go

Go's init function is a special type of function that is executed automatically when a package is initialized. This challenge will test your understanding of how and when init functions are called, and how to use them to set up package-level states or perform one-time initializations. Mastering init functions is crucial for managing package dependencies and ensuring correct program startup.

Problem Description

Your task is to create a Go package that demonstrates the usage and behavior of init functions. You will need to implement an init function within a package that performs some setup. The setup should involve initializing a package-level variable and potentially printing a message to indicate that the initialization has occurred.

Key Requirements:

1. Create a package: Define a new Go package (e.g., initializer).
2. Implement an init function: Within this package, write an init function.
3. Package-level variable: Declare a package-level variable that will be initialized by the init function.
4. Initialization logic: The init function should assign a specific value to the package-level variable and print a confirmation message to stdout.
5. Main package: Create a main package that imports your custom package and accesses the initialized variable to demonstrate that the init function has run successfully.

Expected Behavior:

When the main program is run, the init function in the initializer package should execute automatically before the main function begins. This execution should result in the package-level variable being set and a message being printed to the console. The main function should then be able to use the value of this variable.

Edge Cases to Consider:

• Multiple init functions: What happens if a package has more than one init function?
• Initialization order: How does Go determine the order of execution for init functions, especially across multiple packages? (Though this challenge primarily focuses on a single init per package, understanding this context is important).

Examples

Let's assume you create a package named initializer.

Example 1: Basic Initialization

initializer/initializer.go (Conceptual structure)

package initializer

import "fmt"

var PackageVersion string

func init() {
	fmt.Println("Initializing 'initializer' package...")
	PackageVersion = "1.0.0"
	fmt.Printf("PackageVersion set to: %s\n", PackageVersion)
}

main.go

package main

import (
	"fmt"
	"your_module_path/initializer" // Replace with your actual module path
)

func main() {
	fmt.Println("Starting main function...")
	fmt.Printf("Accessed PackageVersion from initializer: %s\n", initializer.PackageVersion)
	fmt.Println("Finished main function.")
}

Expected Output:

Initializing 'initializer' package...
PackageVersion set to: 1.0.0
Starting main function...
Accessed PackageVersion from initializer: 1.0.0
Finished main function.

Explanation: The initializer package is imported by the main package. Before main's execution begins, Go automatically runs the init function within initializer. This function prints its messages and sets PackageVersion. Subsequently, the main function executes, printing its own messages and accessing the now-initialized initializer.PackageVersion.

Example 2: Multiple init functions within the same package

initializer/initializer.go (Conceptual structure)

package initializer

import "fmt"

var InitializationStatus string
var InitCounter int

func init() {
	fmt.Println("First init function in 'initializer' called.")
	InitializationStatus = "In Progress"
	InitCounter = 1
}

func init() {
	fmt.Println("Second init function in 'initializer' called.")
	InitializationStatus = "Complete"
	InitCounter++ // Now 2
}

main.go

package main

import (
	"fmt"
	"your_module_path/initializer" // Replace with your actual module path
)

func main() {
	fmt.Println("Starting main function...")
	fmt.Printf("InitializationStatus: %s\n", initializer.InitializationStatus)
	fmt.Printf("InitCounter: %d\n", initializer.InitCounter)
	fmt.Println("Finished main function.")
}

Expected Output:

First init function in 'initializer' called.
Second init function in 'initializer' called.
Starting main function...
InitializationStatus: Complete
InitCounter: 2
Finished main function.

Explanation: Go executes init functions within a single package in the order they are declared in the source file. The first init sets InitializationStatus to "In Progress" and InitCounter to 1. The second init then overwrites InitializationStatus to "Complete" and increments InitCounter to 2. The main function then accesses these final values.

Constraints

• Your custom package must be a valid Go package that can be imported by another package.
• The init function(s) must perform actual initialization logic (e.g., assigning to a package variable) and not just print messages.
• The main package must successfully import your custom package and use its initialized data.
• You should only use standard Go libraries (no external dependencies).
• The output must be printed to standard output (stdout).

Notes

• Remember that init functions are executed before main.
• If a package is imported but never used, its init functions (and code) will generally not be executed. However, for this challenge, the main package must actively use a variable initialized by the init function.
• The order of init function execution within a single package is determined by their declaration order in the source file. The order of init function execution across multiple packages is more complex and depends on import dependencies, but for this challenge, focus on a single package first.
• Consider what happens if your init function relies on another package that also has an init function. Go guarantees that a package's init functions will run only after all of its imported packages have been initialized.