The defer statement executes a function (or method) when the enclosing function returns. The arguments are evaluated at the point of the defer; the function call happens upon return.

func data(name string) string {

f := os.Open(name, os.O_RDONLY, 0);

defer f.Close();

contents := io.ReadAll(f);

return contents;

}

Useful for closing fds, unlocking mutexes, etc.

Tracing with defer

func trace(s string) { Print(”entering:”, s); }

func untrace(s string) { Print(”leaving:”, s); }

func a() {

trace(”a”);

defer untrace(”a”);

Print(”in a”)

}

func b() {

trace(”b”);

defer untrace(”b”);

Print(”in b”);

a()

}

func main() { b() }

Args evaluate now, defer later

func trace(s string) string {

Print(”entering:”, s);

return s

}

func un(s string) {

Print(”leaving:”, s)

}

func a() {

defer un(trace(”a”));

Print(”in a”)

}

func b() {

defer un(trace(”b”));

Print(”in b”);

a()

}

func main() { b() }

No related posts.