Getting template sub-type of a templated type

[armstrhu]

Hello,

I was wondering if there was a way to pull the template (sub?)type of a templated type. I know that doesn't make sense, so here is an example.

template<typename T, typename U>
class foo
{
  public:
    foo(T* instance) :
    pointer(instance) {}:

    ~foo() {};

    U& first() {return pointer->first();}

  private:
    T* pointer;
}

int main()
{
  std::vector<int> container;
  container.push_back(2);
  container.push_back(7);
  container.push_back(9);

  foo<std::vector<int>, int> my_foo(container);
  std::cout << my_foo.first() << std::endl;
}

I am looking for a way to access the type 'int' within the container. Would something like
template<typename T<typename U> >
be a way I could access both the fact that it is a std::vector and templated over type int, without having to pass them independently? Thanks

[Disch]

vector (and all other STL containers) typedef value_type as the 'T' template parameter. So you can use that as the sub-type.

So you could do this:

template<typename T>
class foo
{
  typedef typename T::value_type  U;
  // ... 

And it will deduce U from T.

[armstrhu]

Had no clue about that...thanks!