func (w *Writer) SetOutput(out io.Writer) {
	w.mutex.Lock()
	w.printer = newPrinter(out)
	w.mutex.Unlock()
}
func (w *Writer) SetOutput(out io.Writer) {
	w.mutex.Lock()
	w.printer = newPrinter(out)
	w.mutex.Unlock()
}
func ( w * Writer ) SetOutput ( out io . Writer ) { w . mutex . Lock ( ) w . printer = newPrinter ( out ) w . mutex . Unlock ( ) }
// SetOutput sets the output destination for log messages.
SetOutput sets the output destination for log messages .