For Pavel Ilin

simpleSfinae.cc

#include <utility>

template <typename T>
auto func(T& t) -> decltype(std::declval<T>().method(), bool())
{
	return t.method();
}

bool func(int& i) { return 42; }

struct SOk { bool method(); };
struct SFail {};

template<typename T>
constexpr auto funcIsOk(int) -> decltype(func(std::declval<T&>()), bool()) { return true; }
template<typename T>
constexpr auto funcIsOk(...) -> bool { return false; }

int main()
{
	int i = 42;
	func(i); // ok
	SOk sok;
	func(sok); // ok
	SFail sfail;
	//func(sfail); // compile error

static_assert(funcIsOk<SOk>(0), "SOk should be ok");
static_assert(!funcIsOk<SFail>(0), "SFail should fail");
	return 0;
}