Is there a way to inherit from Boost multi index container in C++?

Question

I'm looking for a way to create a base container class that inherits the functionality of the boost multi index container. I want to be able to add other functions to this base class and create other classes that can use this base class's functions and utilize boost's multi index container.

I tried something like:

template < class D, E >
class BoostModelContainer : public boost::multi_index_container<D, E>
{
public:
    D* AddItem( const D& item)
    {
        //code here
    }
};

and then created other classes inheriting the base class like:

class ExampleContainer : public BoostModelContainer< CItem,
boost::multi_index::indexed_by<
  boost::multi_index::ordered_unique< 
     boost::multi_index::tag<id_tag>, boost::multi_index::member< CItem, ItemId, &CItem::m_id > >,
  boost::multi_index::ordered_unique< 
     boost::multi_index::tag<name_tag>, boost::multi_index::member< CItem, String, &CItem::m_name > >
  >
>

But this wouldn't compile. Does anyone have any other ideas or know how to get this to work?

Thank you!!

Don't know enough of your specific case, but I'll drop this here anyway: [Prefer composition over inheritance?](http://stackoverflow.com/questions/49002/prefer-composition-over-inheritance) — user4581301, Oct 12 '16 at 19:14
I don't think composition would work? I am trying to create many various containers with different multi index key structures. And I want all of the containers to have access to base functions, rather than putting the functions in each of the containers. And I want each container to be a boost multi index container. — Trevor Davis, Oct 12 '16 at 19:27
That's just a "Consider your alternatives" comment. There isn't enough in the question to make a good call one way or the other. Sometimes inheritance from a container is appropriate, but usually it isn't. — user4581301, Oct 12 '16 at 20:38

score 2 · Answer 1 · answered Oct 12 '16 at 19:05

2

You're passing two template arguments but your template only takes one.

template < class D, class E >
class BoostModelContainer : public boost::multi_index_container<D, E>
{
public:
    D* AddItem( const D& item)
    {
        //code here
    }
};

answered Oct 12 '16 at 19:05

Still doesn't compile with the additional template argument. I get this error: – Trevor Davis Oct 12 '16 at 19:17
D:\Code\boost\boost_1_62_0\boost/mpl/aux_/has_begin.hpp(20): error C2988: unrecognizable template declaration/definition – Trevor Davis Oct 12 '16 at 19:17
Thanks the problem ended up being elsewhere in the code! – Trevor Davis Oct 13 '16 at 12:46

score 2 · Answer 2 · answered Oct 12 '16 at 21:05

It's a bit hard to figure out exactly what your problem is without a minimal, complete and verifiable example. But rightfold's answer definitely points out the main problem with the code you posted. Essentially you are missing a class keyword in your template declaration:

template < class D, class E >
// missing ---------^^^^^
class BoostModelContainer : public boost::multi_index_container<D, E>
{ /* ... */ };

Apart from that, it should work just fine, as the following complete code example shows (compiles fine, see live demo):

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <string>

template <class D, class E>
class BoostModelContainer : public boost::multi_index_container<D, E>
{
public:
  D* AddItem( const D& item)
  {
    //code here
  }
};

struct Foo
{
  int id;
  std::string name;
};

struct id_tag { };
struct name_tag { };

// Requires -std=c++11    
using ExampleContainer = BoostModelContainer<
  Foo,
  boost::multi_index::indexed_by<
    boost::multi_index::ordered_unique<
      boost::multi_index::tag<id_tag>, boost::multi_index::member<Foo, int, &Foo::id> >,
    boost::multi_index::ordered_unique<
      boost::multi_index::tag<name_tag>, boost::multi_index::member<Foo, std::string, &Foo::name> >
    >
  >;

// works with c++03 as well
struct ExampleContainer2 : public BoostModelContainer<
  Foo,
  boost::multi_index::indexed_by<
    boost::multi_index::ordered_unique<
      boost::multi_index::tag<id_tag>, boost::multi_index::member<Foo, int, &Foo::id> >,
    boost::multi_index::ordered_unique<
      boost::multi_index::tag<name_tag>, boost::multi_index::member<Foo, std::string, &Foo::name> >
    >
  >
{ };

int main()
{
  ExampleContainer ec1;
  ExampleContainer2 ec2;
}

Thanks the problem ended up being elsewhere in the code! – Trevor Davis Oct 13 '16 at 12:46 — Trevor Davis, Oct 13 '16 at 12:46

Is there a way to inherit from Boost multi index container in C++?

2 Answers2