code: func (o *OnceEvery) Do(f func()) {
  	if f == nil {
  		panic("passed function is nil")
  	}
  
  	o.mu.Lock()
  	now := time.Now()
  	ok := o.last.Add(o.Interval).Before(now)
  	if ok {
  		o.last = now
  	}
  	o.mu.Unlock()
  
  	if ok {
  		f()
  	}
  }
docs: // Do calls the function f if and only if Do hits the given periodic interval.
  // In other words Do can be called multiple times during the interval but it
  // gets called only once if it hits the interval tick. So if the interval is
  // 10 seconds, and a total of 100 calls are made during this period, f will
  // be called it every 10 seconds.