code: func (h *HashMap) Update(other *HashMap) *HashMap {
  	updated := h.Copy()
  	other.Iter(func(k, v T) bool {
  		updated.Put(k, v)
  		return false
  	})
  	return updated
  }
docs: // Update returns a new HashMap with elements from the other HashMap put into this HashMap.
  // If the other HashMap contains elements with the same key as this HashMap, the value
  // from the other HashMap overwrites the value from this HashMap.