使用检测到的惯用语可销毁工具

下面是我的实现 is_destructible_v :

template<class T>
struct is_unknown_bound_array : std::false_type
{};
template<class T>
struct is_unknown_bound_array<T[]> : std::true_type
{};

template<typename T, typename U = std::remove_all_extents_t<T>>
using has_dtor = decltype(std::declval<U&>().~U());

template<typename T>
constexpr bool is_destructible_v
    = (std::experimental::is_detected_v<has_dtor, T> or std::is_reference_v<T>)
        and not is_unknown_bound_array<T>::value
        and not std::is_function_v<T>;

template<typename T>
struct is_destructible : std::bool_constant<is_destructible_v<T>>
{};

clang compiled happily and passed all libstdcxx's testsuite 虽然 gcc failed to compile

prog.cc:177:47: error: 'std::declval<int&>()' is not of type 'int&'

 177 | using has_dtor = decltype(std::declval<U&>().~U());    
     |                           ~~~~~~~~~~~~~~~~~~~~^
prog.cc: In substitution of 'template<class T, class U> using has_dtor = decltype (declval<U&>().~ U()) [with T = int&&; U = int&&]':

因此,gcc不能在这方面做SFINAE using has_dtor = decltype(std::declval<U&>().~U()); .

问题:

1. 这里哪个编译器对象是标准的?