In Go, the init() function is a special, built-in function that is called automatically before the main() function runs. It is used to perform package-level initialization or setup that needs to happen before your program starts executing its main logic.

Key points about init()

1. Automatic execution

   • You never call init() manually; Go runs it automatically during program startup.

2. One or more per package

   • A package can have multiple init() functions (even in different files).
   • They are executed in the order they appear within a single file, and across files in lexical order.

3. Purpose

   • Initialize global variables.
   • Set up configuration, logging, or connections.
   • Perform any startup logic that must happen before main().

4. No parameters and no return

   func init() {
       // initialization code
   }
   

Example

package main

import "fmt"

var globalVar int

func init() {
    fmt.Println("Initializing globalVar")
    globalVar = 42
}

func main() {
    fmt.Println("Main starts")
    fmt.Println("globalVar =", globalVar)
}

Output:

Initializing globalVar
Main starts
globalVar = 42

• init() ran automatically before main(), setting up globalVar.

✅ Summary

• init() is a startup hook for a package.
• It runs before main() and is ideal for initialization tasks.
• It cannot take parameters or return values.