#include <cmath>
#include <functional>
#include <iomanip>
#include <iostream>
#include <type_traits>
using namespace std;
 
template <typename T, typename F>
auto func(T && t, F && f)
	-> typename enable_if<is_same<bool, typename result_of<F(T)>::type>::value, bool>::type
{
	return f(t);
}
 
bool is_pi(double d)
{
	// approximately
	return d == 3.1415926;
}
 
int main()
{
	cout << boolalpha << func(42, [](int answer){ return answer == 42; }) << endl;
	cout << boolalpha << func(M_PI, is_pi);
	return 0;
}

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