code: func (h *Hash) CanHaveDefault() bool {
  	return h.KeyType.Type.CanHaveDefault() && h.ElemType.Type.CanHaveDefault()
  }
docs: // CanHaveDefault returns true if the hash type can have a default value.
  // The hash type can have a default value only if both the key type and
  // the element type can have a default value.