std::initializer_list

#include <cassert>
#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 << "constructed with a " << l.size() << "-element list\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()}; // copy list-initialization in return statement
 // this is NOT a use of std::initializer_list
 }
};
 
template<typename T>
void templated_fn(T) {}
 
int main()
{
 S<int> s = {1, 2, 3, 4, 5}; // copy list-initialization
 s.append({6, 7, 8}); // list-initialization in function call
 
 std::cout << "The vector now has " << s.c_arr().second << " ints:\n"; 
 for (auto n : s.v)
 std::cout << n << ' ';
 std::cout << '\n';
 
 std::cout << "Range-for over brace-init-list: \n";
 for (int x : {-1, -2, -3}) // the rule for auto makes this ranged-for work
 std::cout << x << ' ';
 std::cout << '\n';
 
 auto al = {10, 11, 12}; // special rule for auto
 std::cout << "The list bound to auto has size() = " << al.size() << '\n';
 auto la = al; // a shallow-copy of top-level proxy object
 assert (la.begin() == al.begin()); // guaranteed: backing array is the same
 
 std::initializer_list<int> il{-3, -2, -1};
 assert (il.begin()[2] == -1); // note the replacement for absent operator[]
 il = al; // shallow-copy
 assert (il.begin() == al.begin()); // guaranteed
 
// templated_fn({1, 2, 3}); // compiler error! "{1, 2, 3}" is not an expression,
 // it has no type, and so T cannot be deduced
 templated_fn<std::initializer_list<int>>({1, 2, 3}); // OK
 templated_fn<std::vector <int>>({1, 2, 3}); // also OK
}

constructed with a 5-element list
The vector now has 8 ints:
1 2 3 4 5 6 7 8
Range-for over brace-init-list:
-1 -2 -3
The list bound to auto has size() = 3