C++ void_t

#include <type_traits>
#include <iostream>
#include <vector>
using namespace std;

template <typename T, typename = void>
struct RangeConcept : std::false_type {};

template <typename T>
struct RangeConcept<T, 
                       std::void_t<
                                   decltype(  std::declval<T >().begin() ),
                                   decltype(  std::declval<T >().end() )
                                  >
                      >
    : std::true_type {};

template<typename Cont>
void show( Cont c){
    static_assert( RangeConcept< Cont >::value, "must be a range. means.. it has begin() and end()" );
}
int main() { std::vector<int> vec{1,2,3,4,5}; show(vec); }