查找boost multi index标记索引和索引数量 [英] Find boost multi index Tag to index and number of indices

问题描述

我有一个模板类(CrMultiIndex)，它接收boost多索引(GlobalHash)的定义作为模板参数.

I have a template class(CrMultiIndex) that receive as template parameter a definition of boost multi index(GlobalHash).

我需要:

1. 根据使用的索引将统计信息添加到我的模板类中. 因此，我需要一种在初始化时使用现有索引数来调整vector(m_StatsByIndex)大小的方法.
2. 我仍然希望用户根据标签而不是索引号进行搜索. 因此，我需要一种从标记转换为索引号的方法，以便可以根据矢量中的索引更新矢量中的统计信息.

1. To add statistics to my template class according to Index used. So i need a way to resize the vector(m_StatsByIndex) at init with the number of existing indices.
2. I still want the user to search according to tag and not index number. So i need a way to convert from tag to index number so i can update statistics in vector according to index in vector.

我有模板类

template <typename KeysType, typename MultiIndexType>
class CrMultiIndex
{

std::vector<SrStatisticsByIndex> m_StatsByIndex;

public:
MultiIndexType *m_pMultiIndex=NULL; 

CrMultiIndex()
{
    m_pMultiIndex = new MultiIndexType(typename 
    MultiIndexType::ctor_args_list());
}

这是boost多索引容器的定义:

Here is the definition of boost multi index container:

typedef boost::multi_index::multi_index_container<
  CrUsersKeys,
  UsersKey_hash_indices/*,
  bip::allocator<CrUsersKeys,bip::managed_shared_memory::segment_manager>*/
> GlobalHash;

具有根据标签的搜索功能

with a search function according to Tag

template <typename TagType,typename SearchingKey>
typename MultiIndexType::template index<TagType>::type::iterator  
GetIteratorBy(SearchingKey & key)
{
    return  m_pMultiIndex->template get<TagType>().find(key) ;
}

代码位于 http://coliru.stacked-crooked.com/a/d97195a6e4bb7ad4

推荐答案

作为sehe答案的补充，这是对IndexOfTag的重写，它不依赖于未记录的Boost.MultiIndex功能:

As a supplement to sehe's answer, this a rewrite of IndexOfTag that does not depend on undocumented Boost.MultiIndex features:

在Coliru上直播

template<typename MultiIndexContainer,std::size_t N=0>
struct index_position:index_position<MultiIndexContainer,N+1>
{
  using index_type=typename boost::multi_index::nth_index<MultiIndexContainer,N>::type;
  using index_position<MultiIndexContainer,N+1>::case_of;
  static constexpr std::size_t case_of(std::in_place_type_t<index_type>){return N;}
};

template<typename MultiIndexContainer>
struct index_position<
  MultiIndexContainer,
  boost::mpl::size<typename MultiIndexContainer::index_type_list>::value
>
{
  static constexpr void case_of(...){}
};

template <typename MultiIndexContainer,typename Tag>
constexpr std::size_t IndexOfTag()
{
  using index_type=typename boost::multi_index::index<MultiIndexContainer,Tag>::type;
  return index_position<MultiIndexContainer>::case_of(std::in_place_type<index_type>);
}

在C ++ 14中:

In C++14:

在Coliru上直播

template<typename MultiIndexContainer,std::size_t N=0>
struct index_position:index_position<MultiIndexContainer,N+1>
{
  using index_type=typename boost::multi_index::nth_index<MultiIndexContainer,N>::type;
  using index_position<MultiIndexContainer,N+1>::case_of;
  static constexpr std::size_t case_of(index_type*){return N;}
};

template<typename MultiIndexContainer>
struct index_position<
  MultiIndexContainer,
  boost::mpl::size<typename MultiIndexContainer::index_type_list>::value
>
{
  static constexpr void case_of(...){}
};

template <typename MultiIndexContainer,typename Tag>
constexpr std::size_t IndexOfTag()
{
  using index_type=typename boost::multi_index::index<MultiIndexContainer,Tag>::type;
  return index_position<MultiIndexContainer>::case_of((index_type*)(nullptr));
}

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