I want to expand the File_Base virtual interface here to allow me to pass the 'file_data' from the File class without have two sets of code: if (size == 32) 32 bite code else 64 bite code How do I expand the File_base interface? Is there a way to grab the type of a variable passed into a function and reuse it at run time? So that one time doSomething would have the following if the 'file_data' variable was passed in the File_Base interface: void doSomething (boost::shared_ptr<File_Base> const& f) { File<32> a = f->get_File(); // do 32 bit code } While another time the function code be: void doSomething (boost::shared_ptr<File_Base> const& f) { File<64> a = f->get_File(); // do 64 bit code } I would like to be generic so I don't have to repeat the same code. Stephen --------- SAMPLE PROGRAM -------- #include <iostream> #include <boost/shared_ptr.hpp> /*! \brief Type Mapper type */ template <int size> struct Type_Mapper; /*! \brief 32-bit Type Mapper */ template <> struct Type_Mapper<32> { /*! \brief 32-bit type */ typedef uint32_t arch_t; }; /*! \brief 64-bit Type Mapper */ template <> struct Type_Mapper<64> { /*! \brief 64-bit type */ typedef uint64_t arch_t; }; class File_Base { public: virtual uint32_t const get_Size() = 0; }; template <uint32_t size> class File : public File_Base { public: virtual uint32_t const get_Size() { return size; } typename Type_Mapper<size>::arch_t file_data; }; void doSomething (boost::shared_ptr<File_Base> const& f) { // Needs to access the variable 'file_data' in File<size> // Problem: How to expand File_Base interface so that // the variable 'file_data' can be returned without have // code like: if (f->get_Size() == 32) { // do 32 bit code } else { // do 64 bit code } } void create (void) { boost::shared_ptr<File_Base> f (new File<32>()); doSomething (f); } int main (int, char*) { create (); return 0; }