模板参数来提升多索引容器 [英] template parameter to boost multi index container

问题描述

我需要创建一个包含multiindex容器作为存储的通用类。当我编译时，它给出错误如下我已经定义了第n个索引视图。

错误：非模板'nth_index'用作模板

  
 / ** 
 *连接管理员
 * / 
 
 
 
 template< typename T，typename C> 
 class conn_mgr：boost :: noncopyable {
 public：
 / ** 
 * connection ptr 
 * / 
 typedef boost :: shared_ptr conn_ptr_t; 
 
 / ** 
 *连接表类型
 *它是一个多索引容器
 * / 
 typedef boost :: multi_index :: multi_index_container< 
 conn_ptr_t，
 boost :: multi_index :: indexed_by< 
 // sequenced< >，
 boost :: multi_index :: hashed_unique< 
 BOOST_MULTI_INDEX_CONST_MEM_FUN（T，std :: string，T :: id）>，
 boost :: multi_index :: hashed_non_unique< 
 BOOST_MULTI_INDEX_CONST_MEM_FUN（T，std :: string，
 T :: type）>，
 boost :: multi_index :: hashed_non_unique< 
 boost :: multi_index :: composite_key< conn_ptr_t，
 BOOST_MULTI_INDEX_CONST_MEM_FUN（T，
 std :: string，T :: id），
 BOOST_MULTI_INDEX_CONST_MEM_FUN（T，
 std :: string，T :: type）>> > 
 conn_table_t; 
 // ConnectionIdView的typedef 
 typedef conn_table_t :: nth_index< 0> :: type conn_table_by_id_type; 
 
 typedef conn_table_t :: nth_index< 1> :: type conn_table_by_type; 
 
 typedef conn_table_t :: nth_index< 2> :: type conn_table_by_id_type; 
  
 private：
 conn_table_t conn_table_; 
}; 
 
 
 
 

 
 
 
 
这里我如何使用在主。
 
 
 
 int main（int argc，char ** argv）
 {
 typedef conn_mgr& smpp_conn，smpp_config> smpp_conn_mgr_t; 
 smpp_conn_mgr_t conn_mgr; 
} 
 
 
 
 
 
解决方案
使用此语法代替嵌套typedef：
  typedef typename conn_table_t :: template nth_index< 0> :: type conn_table_by_id_type; 
  
  typename 关键字在此处用作限定符，让编译器知道 conn_table_t :: template nth_index< 0> :: type 是一个类型。  typename 的特殊用途仅在模板中有用。
 
 
 
 模板 
 
 
 
 
 
此外，此行是无效：
  typedef boost :: shared_ptr conn_ptr_t; 
  
不能使用typedef模板。你只能使用typedef类型。也许你打算写：
  typedef typename boost :: shared_ptr< T& conn_ptr_t; 
  
 
 
 
 
 
 
最后一个错误：两个typedef具有相同的名称： conn_table_by_id_type  
 
 
 
 
 
 
 code> BOOST_MULTI_INDEX_CONST_MEM_FUN（T，std :: string，T :: id）而不是 BOOST_MULTI_INDEX_CONST_MEM_FUN c>，如此处所记录。
 
 
 
 
 
 
为了回复您最后的评论：此代码段为我编译：
 
 
 <$ pre>  void foo（std :: string id）
 {
 conn_table_by_id_type& id_type_view = conn_table_.template get< 0>（）; 
 typename conn_table_by_id_type :: const_iterator it = id_type_view.find（id）; 
} 
  

其中 foo 在 conn_mgr 模板中的成员函数。

您应该编写帮助方法来获取对您的三个不同的引用 conn_table_ indices。这将使事情更简洁。例如：

  conn_table_by_id_type& by_id_type（）{return conn_table_.template get< 0>（）;} 
 
 void foo2（std :: string id）
 {
 typename conn_table_by_id_type :: const_iterator it = by_id_type （）.find（id）; 
} 
  

I need to create a generic class containing multiindex container as a storage. when I compile, it gives error as below where I have defined nth index view.

error: non-template ‘nth_index’ used as template

/**
 * connection manager
 */


template < typename T, typename C >
class conn_mgr: boost::noncopyable {
public:
    /**
     * connection ptr
     */
    typedef boost::shared_ptr conn_ptr_t;

    /**
     * connection table type
     * It's a multi index container
     */
    typedef  boost::multi_index::multi_index_container <
            conn_ptr_t,
            boost::multi_index::indexed_by <
                    //sequenced < >,
                    boost::multi_index::hashed_unique <
                            BOOST_MULTI_INDEX_CONST_MEM_FUN(T, std::string, T::id)  >,
                    boost::multi_index::hashed_non_unique <
                            BOOST_MULTI_INDEX_CONST_MEM_FUN(T, std::string,
                                    T::type)>,
                    boost::multi_index::hashed_non_unique <
                            boost::multi_index::composite_key < conn_ptr_t,
                                    BOOST_MULTI_INDEX_CONST_MEM_FUN(T,
                                            std::string, T::id),
                                    BOOST_MULTI_INDEX_CONST_MEM_FUN(T,
                                            std::string, T::type ) > > > >
            conn_table_t;
//typedef for ConnectionIdView
typedef conn_table_t::nth_index<0>::type conn_table_by_id_type;

typedef conn_table_t::nth_index<1>::type conn_table_by_type;

typedef conn_table_t::nth_index<2>::type conn_table_by_id_type;
private:
        conn_table_t conn_table_;
 };

and here how I am using in main.

int main( int argc, char** argv )
{
   typedef conn_mgr < smpp_conn, smpp_config > smpp_conn_mgr_t;
   smpp_conn_mgr_t conn_mgr;
}

解决方案

Use this syntax instead for your nested typedefs:

typedef typename conn_table_t::template nth_index<0>::type conn_table_by_id_type;

The typename keyword is used here as a qualifier to let the compiler know that conn_table_t::template nth_index<0>::type is a type. This special use of typename is only necessary within templates.

The template keyword is used here as a qualifier to distingush member templates from other names.

---

Furthermore, this line is invalid:

typedef boost::shared_ptr conn_ptr_t;

You can't typedef templates. You can only typedef types. Perhaps you meant to write:

typedef typename boost::shared_ptr<T> conn_ptr_t;

---

One last error: You're attempting to give two typedefs the same name: conn_table_by_id_type

---

You should use BOOST_MULTI_INDEX_CONST_MEM_FUN(T, std::string, id) instead of BOOST_MULTI_INDEX_CONST_MEM_FUN(T, std::string, T::id), as documented here.

---

In response to your last comment: This snippet compiles for me:

void foo(std::string id)
{
    conn_table_by_id_type& id_type_view = conn_table_.template get<0>();
    typename conn_table_by_id_type::const_iterator it = id_type_view.find(id);
}

Where foo is a member function inside the conn_mgr template. I'm guessing that the above is what you were trying to do.

You should write helper methods that get references to your three different conn_table_ indices. This will make things much more concise. For example:

conn_table_by_id_type & by_id_type() {return conn_table_.template get<0>();}

void foo2(std::string id)
{
    typename conn_table_by_id_type::const_iterator it = by_id_type().find(id);
}

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