cxxtest/check-callable.cc at master · XeCycle/cxxtest · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
#include <type_traits>
#include <utility>

template <class>
struct check_callable_t;

template <class Ret, class... Arg>
struct check_callable_t<Ret(Arg...)> {

  struct fallback {};
  struct preferred : fallback {};

  template <class F>
  constexpr static auto check_impl(F&& f, preferred)
    -> decltype(static_cast<Ret>(((F&&)f)(std::declval<Arg>()...)), std::true_type())
  {
    return {};
  }

  template <class F>
  constexpr static std::false_type check_impl(F&&, fallback)
  {
    return {};
  }

  template <class F>
  constexpr static auto check(F&& f)
  {
    return check_callable_t::check_impl((F&&)f, preferred());
  }

};

template <class Signature, class F>
constexpr auto check_callable(F&& f)
{
  return check_callable_t<Signature>::check((F&&)f);
}

auto result = check_callable<void()>([](auto&&...) {});

static_assert(decltype(result)::value, "");