How can I get the depth of a multidimensional std::vector at compile time?

Question

I have a function that takes a multidimensional std::vector and requires the depth (or the number of dimensions) to be passed in as a template parameter. Instead of

Answer 1

Assuming that a container is any type that has value_type and iterator member types (standard library containers satisfy this requirement) or a C-style array, we can easily generalize Cruz Jean's solution:

template
struct rank : std::integral_constant {};

// C-style arrays
template
struct rank 
    : std::integral_constant::value> {};

template
struct rank 
    : std::integral_constant::value> {};

// Standard containers
template
struct rank> 
    : std::integral_constant::value> {};

int main() {
    using T1 = std::list, 4>>>;
    using T2 = std::list[4]>>;

    std::cout << rank();  // Output : 4
    std::cout << rank();  // Output : 4
}

Container types can be further restricted if needed.