code: func (c *Cache) Put(ctx context.Context, key storage.CacheKey, val []byte, exp time.Duration) {
  	c.mu.Lock()
  	defer c.mu.Unlock()
  
  	if c.cacheMap == nil {
  		c.cacheMap = make(map[storage.CacheKey][]byte)
  	}
  
  	c.cacheMap[key] = val
  }
docs: // Put implements storage.Cache.