#include <gsl/pointers>
#include <iostream>

void f(gsl::not_null<const int *> i) {
  std::cout << *i << '\n';
}

int main() {
  int i = 42;
  f(&i); // no matching function for call to 'f'
         // note: candidate function not viable: no known conversion from 'int *' to 'gsl::not_null<const int *>' for 1st argument
  return 0;
}