How to 'rename' a template instantiation without using inheritance?

Question

Suppose you are using a template class in your application, like e.g. std::tuple (or std::shared_ptr, or whatever), and you have instantiations like this:

typedef std::tuple<Book,Library> BookLibrary;
typedef std::tuple<Book,Chapter,Reader> BookChapterReader;

And then you are using these instantiations in other templated classes, e.g. an std::map as member in a class:

class X
   {
   ...
   private:
      std::map<Library,BookChapterReader> m_data;
   };

Then the resulting PDB file will contain descriptions like this (seen with the DBH utility of the Microsoft Debugging Tools):

std::_Tree<std::_Tmap_traits<Library,std::tr1::tuple<Book,Chapter,Reader,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil>,std::less<Library>,std::allocator<std::pair<Library const ,std::tr1::tuple<Book,Chapter,Reader,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil,std::tr1::_Nil> > >,0> >

If you have quite some of these constructions then the PDB file grows very quickly, until a moment where the linker just refuses to link your application (apparently, the PDB file has a limit of 1 GB).

A solution could be to create a subclass of the templated instantiation, like this:

class BookChapterReader : public std::tuple<Book,Chapter,Reader>
   {
   };

This will seriously shorten the symbols. The one mentioned above now is:

std::_Tree<std::_Tmap_traits<Library,BookChapterReader,std::less<Library>,std::allocator<std::pair<Library const ,BookChapterReader> >,0> >

However, by using inheritance we introduce the risk that one might add data to the inherited class, and we might need to introduce a virtual destructor (which I don't want here in this case).

It seems that C++ (or Visual Studio?) has a limitation:

• If I just use a typedef, the symbols become much too large
• If I use inheritance it might seem I want to extend the std::tuple, but I don't want to do this

Isn't there a cleaner way to 'rename' a template instatiation without using inheritance?

Answer 1

Create your own version of both less and allocator implementations instead of relying on the default which have a very long name.

std::map< Library, BookChapterReader, CompareLibrary, MyAllocator > m_data;

The allocator class is super simple and so is the Compare functor.