Defer

Context

The defer statement postpones the execution of a function until the surrounding function returns. It is commonly used for cleanup actions (closing files, unlocking mutexes). Multiple deferred calls are executed in LIFO (last‑in‑first‑out) order.

Example

Use defer to close a file and to demonstrate LIFO order.

Code example

package main

import (
    "fmt"
    "os"
)

func main() {
    // LIFO example
    defer fmt.Println("first deferred (executed last)")
    defer fmt.Println("second deferred")
    defer fmt.Println("third deferred (executed first)")

    // Practical: file closing
    file, err := os.Create("example.txt")
    if err != nil {
        fmt.Println("Error creating file")
        return
    }
    defer file.Close() // guaranteed to run before main returns

    file.WriteString("Hello, defer!")
    fmt.Println("File written")
}

Output

File written
third deferred (executed first)
second deferred
first deferred (executed last)

Useful links

• Go by Example: Defer
• Go spec: Defer statements