#include <cstdio>

class tag;

template<class>
struct type { friend constexpr auto get(type); };

template<class TKey, class TValue>
struct set { friend constexpr auto get(TKey) { return TValue{}; } };

struct pituh { auto operator ()(auto value) { std::printf("called %d", value); } };

void foo() {            // never called
  if constexpr(false) { // never true
    if (false) {        // never true
        constexpr auto call = pituh{};
        void(set<type<tag>, decltype(call)>{});
    }
  }
}

int main() {
  get(type<tag>{})(42); // prints called 42
}