c++ - 如何更新 boost::multi_index_container 中的重叠索引？

Question

我使用的是 boost 1.48.0，我没有升级选项。

我构建了一个 multi_index_container，其中的索引具有重叠的条件。共享相同索引标准的索引如何生效，如以下示例所示？示例代码的最后一行暗示了我的要求。

struct street_address_key : composite_key<
    t_postal_address
    , const_mem_fun<const_mem_fun<t_postal_address, string, &t_postal_address::street_name>>
    , const_mem_fun<const_mem_fun<t_postal_address, long, &t_postal_address::house_number>>
    , const_mem_fun<const_mem_fun<t_postal_address, string, &t_postal_address::city>>
    , const_mem_fun<const_mem_fun<t_postal_address, string, &t_postal_address::state>>
    , const_mem_fun<const_mem_fun<t_postal_address, long, &t_postal_address::zip_code>>
> {};

multi_index<
    t_postal_address
    indexed_by<
        ordered_unique<street_address_key>
        , ordered_non_unique<const_mem_fun<t_postal_address, string, &t_postal_address::name>>
        , ordered_non_unique<const_mem_fun<const_mem_fun<t_postal_address, string, &t_postal_address::street_name>>
        , ordered_non_unique<const_mem_fun<const_mem_fun<t_postal_address, long, &t_postal_address::house_number>>
        , ordered_non_unique<const_mem_fun<const_mem_fun<t_postal_address, string, &t_postal_address::city>>
        , ordered_non_unique<const_mem_fun<const_mem_fun<t_postal_address, string, &t_postal_address::state>>
        , ordered_non_unique<const_mem_fun<const_mem_fun<t_postal_address, long, &t_postal_address::zip_code>>
    >
> t_address_book;

...

t_address_book::nth_element<0>::type::iterator address_iter = book.find(some_address_tuple);

book.modify(address_iter, modify_city_method);

auto city_range = book.get<4>().equal_range( \*???*\ );

城市索引与 street_address_key 共享相同的标准。据我了解，通过 street_address_key 进行修改将确保索引得到适当更新。但是“城市”索引的状态是什么？它是否已更新以反射(reflect)城市名称的变化？或者它处于损坏状态？我还能找到与旧城相同的地址索引吗？我必须单独更新这个索引吗？我可以调用空操作修改器来更新索引吗？

// Presume I have the city element from the index.
// Is this supposed to update the city index after it was modified above?

book.get<4>().modify(city_iter, [](t_postal_address &) {});

Answer 1

在我看来应该没有问题:

文档提到:

Effects: Calls mod(e) where e is the element pointed to by position and rearranges *position into all the indices of the multi_index_container. Rearrangement is successful if

• the index is non-unique OR no other element exists with equivalent key,
• AND rearrangement is allowed by all other indices of the multi_index_container. If the rearrangement fails, the element is erased.

这意味着所有索引都已更新。请注意，所有索引原则上都可以拒绝编辑。您可能希望使用回滚来防止数据丢失。