Go by Example: Defer

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" import "os"
Suppose we wanted to create a file, write to it, and then close when we’re done. Here’s how we could do that with `defer`.	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") f.Close() }

Running the program confirms that the file is closed after being written.

$ go run defer.go
creating
writing
closing