#include <iostream>
using namespace std;
 
template <bool isConstexpr>
struct f_impl;
 
template <>
struct f_impl<false>
{
	static int f(int a)
	{
		cout << "well, I'm not constexpr f()\n";
		return a;
	}
};
 
constexpr int f_constexpr(int a)
{
	return a;
}
 
template <>
struct f_impl<true>
{
	static constexpr int f(int a)
	{
		return f_constexpr(a);
	}
};
 
 
#define f(a) f_impl<noexcept(f_constexpr(a))>::f(a)
 
int main(int argc, char* argv[]) {
	constexpr int a = f(7);
    cout << "constexpr was called..." << endl; 
	int c = f(argc);
    cout << "non constexpr was called, I guess..." << endl; 
	cout << a << endl;
	cout << c << endl;
 
}

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