Defer

Context

The defer statement postpones the execution of a function until the surrounding function returns (after a return or when panic occurs). Deferred calls are stacked and executed in LIFO order (last in, first out).

Typical uses: closing files, releasing locks, cleanup.

Example

Demonstrate the order of defer execution and their usefulness.

Code example

package main

import "fmt"

func main() {
    fmt.Println("start")

    // Deferred calls are stacked
    defer fmt.Println("first defer (executed last)")
    defer fmt.Println("second defer")
    defer fmt.Println("third defer (executed first)")

    fmt.Println("end of function")
    // Deferred calls execute here, after implicit return
}

Output

start
end of function
third defer (executed first)
second defer
first defer (executed last)

Real use: file closing

f, err := os.Open("file.txt")
if err != nil {
    return err
}
defer f.Close() // guaranteed closure

Useful links

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