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" "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")`
	`}`
It’s important to check for errors when closing a file, even in a deferred function.	`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) } }`

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

$ go run defer.go
creating
writing
closing

Next example: Recover.