std::initializer_list<T>::initializer_list

#include <initializer_list>
#include <iostream>
#include <vector>
 
template <class T>
struct S {
    std::vector<T> v;
    S(std::initializer_list<T> l) : v(l) {
         std::cout << "  " << l.size() << "- \n";
    }
    void append(std::initializer_list<T> l) {
        v.insert(v.end(), l.begin(), l.end());
    }
    std::pair<const T*, std::size_t> c_arr() const {
        return {&v[0], v.size()};  //      return
                                   //    std::initializer_list
    }
};
 
template <typename T>
void templated_fn(T) {}
 
int main()
{
    S<int> s = {1, 2, 3, 4, 5}; //   
    s.append({6, 7, 8});      //     
 
    std::cout << "   " << s.c_arr().second << " int:\n";
 
    for (auto n : s.v)
        std::cout << n << ' ';
    std::cout << '\n';
 
    std::cout << " for  ----: \n";
 
    for (int x : {-1, -2, -3}) //   auto    for 
        std::cout << x << ' ';
    std::cout << '\n';
 
    auto al = {10, 11, 12};   //    auto
 
    std::cout << ",   auto,  size() = " << al.size() << '\n';
 
//    templated_fn({1, 2, 3}); //  ! "{1, 2, 3}"   ,
                             //    ,   T    
    templated_fn<std::initializer_list<int>>({1, 2, 3}); // OK
    templated_fn<std::vector<int>>({1, 2, 3});           //  OK
}