Question

Example

#include <vector>
#include <cassert>

template <typename Cont, typename... Rest>
void f(Cont& c, Rest&... rest)
{
    assert(c.size() == ???);
}


int main()
{
    std::vector<int> v1(10);
    std::vector<int> v2(10);
    std::vector<int> v3(10);
    std::vector<int> v4(10);

    f(v1, v2, v3, v4);
}

I want to make sure that all the containers passed to a function are the same size. However, the function is a variadic template that takes an arbitrary number of containers of the same type. Is this possible?

Answer 1

#include <vector>
#include <cassert>

template <typename Size>
bool check_size(Size) {
  return true;
}

template <typename Size, typename Cont, typename... Rest>
bool check_size(Size expected, Cont& c, Rest&... rest) {
  return (c.size() == expected && check_size(expected, rest...));
}

template <typename Cont, typename... Rest>
void f(Cont& c, Rest&... rest)
{
  assert(check_size(c.size(), rest...));
}

int main()
{
    std::vector<int> v1(10);
    std::vector<int> v2(10);
    std::vector<int> v3(10);
    std::vector<int> v4(10);

    f(v1, v2, v3, v4);
}