code: func NewSimpleLRUCache(capacity uint, guard float64, quota uint64) *SimpleLRUCache {
  	if capacity <= 0 {
  		panic("capacity of LRU Cache should be positive.")
  	}
  	return &SimpleLRUCache{
  		capacity: capacity,
  		size:     0,
  		quota:    quota,
  		guard:    guard,
  		elements: make(map[string]*list.Element),
  		cache:    list.New(),
  	}
  }
docs: // NewSimpleLRUCache creates a SimpleLRUCache object, whose capacity is "capacity".
  // NOTE: "capacity" should be a positive value.