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copied!<p>I think this will do:-</p> <p>(<strong>Corrected</strong> including aschepler's test case)</p> <pre><code>#include <type_traits> template<typename Func, typename Ret, typename... Args> struct returns_a { template<typename F, typename ...As> static constexpr bool test( decltype(std::declval<F>()(std::declval<As>()...)) * prt) { return std::is_same<Ret *,decltype(prt)>::value; } template <typename F, typename ...As> static constexpr bool test(...) { return false; } static const bool value = test<Func,Args...>(static_cast<Ret *>(0)); }; // Testing... #include <iostream> void fn0(); int fn1(int); int fn2(int,int); struct cls{}; struct fntor { int operator()(int i) { return 1; } }; auto lamb0 = [](int i) -> int { return i; }; struct B {}; struct D : public B {}; auto lamb1 = []{ return B{}; }; int main() { std::cout << returns_a<decltype(fn0),void>::value << std::endl; // 1 std::cout << returns_a<decltype(fn1),int,int>::value << std::endl; // 1 std::cout << returns_a<decltype(fn1),int,double>::value << std::endl; // 1 std::cout << returns_a<decltype(fn1),double,int>::value << std::endl; // 0 std::cout << returns_a<decltype(fn1),char,int>::value << std::endl; // 0 std::cout << returns_a<decltype(fn1),unsigned,int>::value << std::endl; // 0 std::cout << returns_a<decltype(fn2),int,int,int>::value << std::endl; // 1 std::cout << returns_a<decltype(fn2),int,char,float>::value << std::endl; // 1 std::cout << returns_a<cls,int,int>::value << std::endl; // 0 std::cout << returns_a<fntor,int,int>::value << std::endl; // 1 std::cout << returns_a<decltype(lamb0),int,int>::value << std::endl; // 1 std::cout << returns_a<double,int,int>::value << std::endl; // 0 std::cout << returns_a<decltype(lamb1), D>::value << std::endl; //0 return 0; } </code></pre> <p>(Built with clang 3.2, gcc 4.7.2, gcc 4.8.1)</p>

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