Question

I’d like to write a function template like that:

template< typename L<T> >  // does not work
void do_sth(L<T>& list){
    T value = 0;
    list.push_back(value);
}

This means, in the template I’d like to work with containers offering “push_back”, but also with the type stored inside that container.

A workaround would be

template< typename T >
void do_sth(typename std::list<T>& list){
    T value = 0;
    list.push_back(value);
}

// call    
std::list<double> list;
do_sth<double>(list);

which is redundant because a) I already specified “double” when declaring “list” and b) the function would not work with a std::vector, although the implementation would perfectly fit.

Does anyone know how to accomplish that?

Answer 1

That’s one of the reasons STL containers provide the value_type typedef:

template< typename Container >
void do_sth(Container& list){
    typename Container::value_type value = 0;
    list.push_back(value);
}

Your workaround would also work with a plain call to do_sth(list); due to template argument deduction.