code: func (c *Cache) MustGet(key Key) interface{} {
  	value, err := c.Get(key)
  	if err != nil {
  		panic(fmt.Sprintf("error returned from Get: %s", err))
  	}
  	return value
  }
docs: // MustGet returns the value for the given key. If the key doesn't
  // exist then the initializer is invoked to create the value and the
  // key is inserted. If an error is returned during initialization of the
  // value then this function will panic.