code: func (k *Store) Visit(cb func(string, interface{}) bool) {
  	// Read-only lock
  	k.mu.RLock()
  	defer k.mu.RUnlock()
  
  	for k, v := range k.db {
  		if !cb(k, v) {
  			break
  		}
  	}
  }
docs: // Visit walks through the entire store via a function; return false from
  // your visitor function to halt the walk