What does this C++ snippet output?

1#include <iostream>
2 
3struct Once {
4  Once() { std::cout << "init\n"; }
5};
6Once& instance() {
7  static Once o;
8  return o;
9}
10int main() {
11    std::cout << "before\n";
12    instance();
13    instance();
14    std::cout << "after\n";
15}