Given a (reduced) implementation of the detection idiom
namespace type_traits
{
template<typename... Ts>
using void_t = void;
namespace detail
{
template<typename, template<typename...> class, typename...>
struct is_detected : std::false_type {};
template<template<class...> class Operation, typename... Arguments>
struct is_detected<void_t<Operation<Arguments...>>, Operation, Arguments...> : std::true_type {};
}
template<template<class...> class Operation, typename... Arguments>
using is_detected = detail::is_detected<void_t<>, Operation, Arguments...>;
template<template<class...> class Operation, typename... Arguments>
constexpr bool is_detected_v = detail::is_detected<void_t<>, Operation, Arguments...>::value;
}
we can easily check if a class foo contains a member function bar
struct foo {
int const& bar(int&&) { return 0; }
};
template<class T>
using bar_t = decltype(std::declval<T>().bar(0));
int main()
{
static_assert(type_traits::is_detected_v<bar_t, foo>, "not detected");
return 0;
}
However, as you can see, we cannot detect that foo::bar's argument type is int&&. The detection succeeds, cause 0 can be passed to foo::bar. I know that there are plenty of options to check for the exact signature of a (member) function. But I would like to know, if it's possible to modify this detection toolkit in order to detect that foo::bar's argument type is exactly int&&.
[I've created a live demo of this example.]