code: func (table *RegommendTable) Exists(key interface{}) bool {
  	table.RLock()
  	defer table.RUnlock()
  	_, ok := table.items[key]
  
  	return ok
  }
docs: // Test whether an item exists in the engine. Unlike the Value method
  // Exists neither tries to fetch data via the loadData callback nor
  // does it keep the item alive in the engine.