Defer
Examples in
Go
Defer is used to ensure that a function call is performed later in a program’s execution, usually for purposes of cleanup. defer is often used where e.g. ensure and finally would be used in other languages.
package main
import (
"fmt"
"os"
)
func main() {
// Immediately after getting a file object with createFile, we defer the closing of that file with closeFile.
// This will be executed at the end of the enclosing function (main), after writeFile has finished.
f := createFile("/tmp/defer.txt")
defer closeFile(f)
writeFile(f)
}
func createFile(p string) *os.File {
fmt.Println("creating")
f, err := os.Create(p)
if err != nil {
panic(err)
}
return f
}
func writeFile(f *os.File) {
fmt.Println("writing")
fmt.Fprintln(f, "data")
}
func closeFile(f *os.File) {
fmt.Println("closing")
err := f.Close()
if err != nil {
fmt.Fprintf(os.Stderr, "error: %v\n", err)
os.Exit(1)
}
}