在ExecutorService的提交和ExecutorService的执行之间进行选择(Choose between ExecutorService's submit and ExecutorService's execute)

 你猜到了。 
 使用pack模板，并“简化”一点： 
 
template <typename...> struct pack {}; // To be potentially introduced in C++1Z

template <typename, typename, typename=void>
struct Exists_impl : std::false_type {};

template <typename R, typename... Args>
struct Exists_impl<R, pack<Args...>,
  std::enable_if_t<std::is_same<decltype(foo(std::declval<Args>()...)), R>::value>>
    : std::true_type {};

template <typename R, typename... Args>
using Exists = Exists_impl<R, pack<Args...>>;
 
 演示 。 
 请注意，此模板永远无法通过ADL查找void(int)等函数，因为在这种情况下，关联的命名空间集合为空。 必须在定义时声明这些函数。 
 使用is_convertible而不是is_same来检查返回类型也是可行的，具体取决于用例。 

You guessed it.
 Use a pack template, and "simplify" a bit:
 
template <typename...> struct pack {}; // To be potentially introduced in C++1Z

template <typename, typename, typename=void>
struct Exists_impl : std::false_type {};

template <typename R, typename... Args>
struct Exists_impl<R, pack<Args...>,
  std::enable_if_t<std::is_same<decltype(foo(std::declval<Args>()...)), R>::value>>
    : std::true_type {};

template <typename R, typename... Args>
using Exists = Exists_impl<R, pack<Args...>>;
 
Demo.
 Note that this template will never be able to find functions like void(int) via ADL, as the set of associated namespaces is empty in such cases. Those functions must be declared at the point of definition.
 Also it might be feasible to use is_convertible instead of is_same for the check of the return type, depending on the use-case.