The following code example is taken from the book
C++17 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2017
The code is licensed under a Creative Commons Attribution 4.0 International License. Creative Commons License

// raw code

#include <iostream>

template<typename T>
void call(T op1, T op2)

void f1() {
  std::cout << "f1()\n";
void f2() noexcept {
  std::cout << "f2()\n";

int main()
  call(f1, f2);  // ERROR since C++17