Question

Is it possible to create template to the initialization like:

template <typename C> typename C::value_type  fooFunction(C& c) {...};
std::vector<string> vec_instance;
fooFunction(cont<0>(vec_instance));
fooFunction(cont<1>(vec_instance));

In general i’m interested is it possible to specify template using integer (ie. 0) instead of true type name.
And how to achieve above?

Answer 1

I’m not completely clear on what you’re asking, but the following snippet works for me:

#include <iostream>
#include <vector>
#include <string>

using namespace std;

template <typename C>
typename C::value_type  fooFunction(const C & c) { return 0; };
/* note that fooFunction takes a ref-to-const, not a reference  */ 

template<int N>
struct cont
{
public:
   typedef int value_type;
   cont(vector<string> vec) {};
};

int main()
{
std::vector<string> vec_instance;
fooFunction(cont<0>(vec_instance));
fooFunction(cont<1>(vec_instance));
}

Two changes worth noting:

1. An integer is not a type, so if cont is declared template <typename T>, what you have written will not work. template <int N> is the proper way to parameterize over an integral value, as templatetypedef mentioned.

2. I’m not sure how cont<> is defined, but from your usage it must be an object you are constructing as a temporary. You will have trouble passing this temporary as a reference into fooFunction. Note that my example above passes C as reference-to-const instead.