使用纯虚函数来提升多索引容器

Question

我想创建一个类型A的multi_index_container，它存储C类型的对象，它是从B派生而来的。问题是A中我有纯虚函数。当我尝试编译它时，我得到了最底层描述的错误。

• 我想这不可能做对吗？

• 整个想法是否有缺陷？

代码

#include <iostream>
#include <string>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/identity.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/hashed_index.hpp>
#include <boost/multi_index/mem_fun.hpp>



using  boost::multi_index_container;
using namespace boost::multi_index;

class A{
public:
        virtual void print()=0;
        std::string getName() const {return name;};
        void setName(std::string s){name=s;};
        std::string name;
};

template<typename T>
class B: public A{
public:
        virtual void print(){std::cout<<"B"<<name<<std::endl;}
};

template<typename T>
class C: public B<T> {
public:
        virtual void print(){std::cout<<"C"<<reinterpret_cast<A*>(this)->name<<std::endl;}
};


typedef multi_index_container<
        A,
        indexed_by<
            hashed_non_unique<const_mem_fun<A, std::string, &A::getName>>
        >
> Container;


int main(){

        C<int>    c;
        c.setName("c");
        Container    container;
        container.insert(c);
        return 0;
}

错误

In file included from /usr/local/include/boost/aligned_storage.hpp:20:0,
             from /usr/local/include/boost/type_traits/aligned_storage.hpp:11,
             from /usr/local/include/boost/multi_index/detail/index_node_base.hpp:17,
             from /usr/local/include/boost/multi_index/detail/node_type.hpp:23,
             from /usr/local/include/boost/multi_index/detail/index_base.hpp:21,
             from /usr/local/include/boost/multi_index/detail/base_type.hpp:21,
             from /usr/local/include/boost/multi_index_container.hpp:33,
             from wierdInheritance.cpp:13:
/usr/local/include/boost/type_traits/alignment_of.hpp: In instantiation of ‘boost::detail::alignment_of_hack<A>’:
/usr/local/include/boost/type_traits/alignment_of.hpp:71:5:   instantiated from ‘const size_t boost::detail::alignment_of_impl<A>::value’
/usr/local/include/boost/type_traits/alignment_of.hpp:89:1:   instantiated from ‘boost::alignment_of<A>’
/usr/local/include/boost/multi_index/detail/index_node_base.hpp:42:32:   instantiated from ‘boost::multi_index::detail::pod_value_holder<A>’
/usr/local/include/boost/multi_index/detail/index_node_base.hpp:46:8:   instantiated from ‘boost::multi_index::detail::index_node_base<A, std::allocator<A> >’
/usr/local/include/boost/multi_index/detail/hash_index_node.hpp:116:8:   instantiated from ‘boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<A, std::allocator<A> > >’
/usr/local/include/boost/multi_index/hashed_index.hpp:108:54:   instantiated from ‘boost::multi_index::detail::hashed_index<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName>, boost::hash<std::basic_string<char> >, std::equal_to<std::basic_string<char> >, boost::multi_index::detail::nth_layer<1, A, boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName> > >, std::allocator<A> >, boost::mpl::vector0<mpl_::na>, boost::multi_index::detail::hashed_non_unique_tag>’
/usr/local/include/boost/multi_index_container.hpp:70:7:   instantiated from ‘boost::multi_index::multi_index_container<A, boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName> > > >’
wierdInheritance.cpp:57:19:   instantiated from here
/usr/local/include/boost/type_traits/alignment_of.hpp:42:7: error: cannot declare field ‘boost::detail::alignment_of_hack<A>::t’ to be of abstract type ‘A’
wierdInheritance.cpp:24:7: note:   because the following virtual functions are pure within ‘A’:
wierdInheritance.cpp:26:22: note:   virtual void A::print()
In file included from /usr/local/include/boost/multi_index_container.hpp:20:0,
             from wierdInheritance.cpp:13:
/usr/local/include/boost/detail/allocator_utilities.hpp: In function ‘void boost::detail::allocator::construct(void*, const Type&) [with Type = A]’:
/usr/local/include/boost/multi_index/detail/index_base.hpp:88:5:   instantiated from ‘boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::node_type* boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::insert_(boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::value_param_type, boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::node_type*) [with Value = A, IndexSpecifierList = boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName> > >, Allocator = std::allocator<A>, boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::node_type = boost::multi_index::detail::index_node_base<A, std::allocator<A> >, boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::value_param_type = const A&]’
/usr/local/include/boost/multi_index/hashed_index.hpp:701:63:   instantiated from ‘boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::node_type* boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::insert_(boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::value_param_type, boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::node_type*) [with KeyFromValue = boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName>, Hash = boost::hash<std::basic_string<char> >, Pred = std::equal_to<std::basic_string<char> >, SuperMeta = boost::multi_index::detail::nth_layer<1, A, boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName> > >, std::allocator<A> >, TagList = boost::mpl::vector0<mpl_::na>, Category = boost::multi_index::detail::hashed_non_unique_tag, boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::node_type = boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<A, std::allocator<A> > >, typename SuperMeta::type::node_type = boost::multi_index::detail::index_node_base<A, std::allocator<A> >, boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::value_param_type = const A&]’
/usr/local/include/boost/multi_index_container.hpp:488:40:   instantiated from ‘std::pair<typename boost::multi_index::detail::multi_index_base_type<Value, IndexSpecifierList, Allocator>::type::node_type*, bool> boost::multi_index::multi_index_container<Value, IndexSpecifierList, Allocator>::insert_(const Value&) [with Value = A, IndexSpecifierList = boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName> > >, Allocator = std::allocator<A>, typename boost::multi_index::detail::multi_index_base_type<Value, IndexSpecifierList, Allocator>::type::node_type = boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<A, std::allocator<A> > >]’
/usr/local/include/boost/multi_index/detail/index_base.hpp:150:30:   instantiated from ‘std::pair<typename boost::multi_index::detail::multi_index_node_type<Value, IndexSpecifierList, Allocator>::type*, bool> boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::final_insert_(boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::value_param_type) [with Value = A, IndexSpecifierList = boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName> > >, Allocator = std::allocator<A>, typename boost::multi_index::detail::multi_index_node_type<Value, IndexSpecifierList, Allocator>::type = boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::index_node_base<A, std::allocator<A> > >, boost::multi_index::detail::index_base<Value, IndexSpecifierList, Allocator>::value_param_type = const A&]’
/usr/local/include/boost/multi_index/hashed_index.hpp:254:61:   instantiated from ‘std::pair<boost::multi_index::detail::hashed_index_iterator<boost::multi_index::detail::hashed_index_node<typename SuperMeta::type::node_type>, boost::multi_index::detail::bucket_array<typename SuperMeta::type::final_allocator_type> >, bool> boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::insert(boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::value_param_type) [with KeyFromValue = boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName>, Hash = boost::hash<std::basic_string<char> >, Pred = std::equal_to<std::basic_string<char> >, SuperMeta = boost::multi_index::detail::nth_layer<1, A, boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::const_mem_fun<A, std::basic_string<char>, &A::getName> > >, std::allocator<A> >, TagList = boost::mpl::vector0<mpl_::na>, Category = boost::multi_index::detail::hashed_non_unique_tag, typename SuperMeta::type::final_allocator_type = std::allocator<A>, typename SuperMeta::type::node_type = boost::multi_index::detail::index_node_base<A, std::allocator<A> >, boost::multi_index::detail::hashed_index<KeyFromValue, Hash, Pred, SuperMeta, TagList, Category>::value_param_type = const A&]’
wierdInheritance.cpp:58:27:   instantiated from here
/usr/local/include/boost/detail/allocator_utilities.hpp:178:3: error: cannot allocate an object of abstract type ‘A’
wierdInheritance.cpp:24:7: note:   since type ‘A’ has pure virtual functions

Answer 1

您无法定义A的容器，但您可以将指针容器（例如shared_ptr）定义为A：

typedef multi_index_container<
        A *,
        indexed_by<
            hashed_non_unique<const_mem_fun<A, std::string, &A::getName>>
        >
> Container;

或：

typedef multi_index_container<
        boost::shared_ptr<A>,
        indexed_by<
            hashed_non_unique<const_mem_fun<A, std::string, &A::getName>>
        >
> Container;