任何包含std::tuple<std::any>的内容都无法编译
任何包含std::tuple<std::any>的内容都无法编译
提问于 2020-12-06 00:29:39
我意识到嵌套的性病：：任何的都是一个坏主意。尽管如此，我还是遇到了一些让我抓狂的东西，我只是想弄明白为什么编译器会窒息。考虑以下代码行(假设arg变量是包含另一个std::any的std::any)：
auto result = std::any_cast<std::any>(arg);那行编译得很好。现在，考虑这一行，其中包含包含另一个std::any的std::tuple的std::any: any：
auto result = std::any_cast<std::tuple<std::any>>(arg);现在编译器会爆炸。以下是我所犯的错误：
In file included from /home/james/git/trogdor-pp/src/core/event/triggers/luaeventtrigger.cpp:1:
In file included from /home/james/git/trogdor-pp/src/core/include/trogdor/game.h:5:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:37:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/new:40:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/exception:144:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/nested_exception.h:40:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/move.h:55:
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:132:31: error: no member named 'value' in 'std::is_copy_constructible<std::tuple<std::any> >'
: public conditional<_B1::value, _B2, _B1>::type
~~~~~^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:170:17: note: in instantiation of template class 'std::__and_<std::is_copy_constructible<std::tuple<std::any> >, std::is_constructible<std::tuple<std::any>, const std::tuple<std::any> &> >' requested here
enable_if<__and_<is_copy_constructible<_Tp>,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:175:5: note: in instantiation of template type alias '__any_constructible' requested here
using __any_constructible_t =
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:181:56: note: in instantiation of template type alias '__any_constructible_t' requested here
__any_constructible_t<_Tp, _ValueType&&> = true,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:183:7: note: while substituting prior template arguments into non-type template parameter [with _ValueType = const std::tuple<std::any> &, _Tp = std::tuple<std::any>, _Mgr = std::any::_Manager_external<std::tuple<std::any> >]
any(_ValueType&& __value)
^~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:884:56: note: while substituting deduced template arguments into function template 'any' [with _ValueType = const std::tuple<std::any> &, _Tp = (no value), _Mgr = (no value), $3 = (no value), $4 = (no value)]
: public __bool_constant<__is_constructible(_Tp, _Args...)>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:884:32: note: (skipping 2 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
: public __bool_constant<__is_constructible(_Tp, _Args...)>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:908:14: note: in instantiation of template class 'std::__is_copy_constructible_impl<std::tuple<std::any>, true>' requested here
: public __is_copy_constructible_impl<_Tp>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:109:14: note: in instantiation of template class 'std::is_copy_constructible<std::tuple<std::any> >' requested here
: public conditional<_B1::value, _B1, _B2>::type
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:358:16: note: in instantiation of template class 'std::__or_<std::is_reference<std::tuple<std::any> >, std::is_copy_constructible<std::tuple<std::any> > >' requested here
{ return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:481:26: note: in instantiation of function template specialization 'std::any::__is_valid_cast<std::tuple<std::any> >' requested here
static_assert(any::__is_valid_cast<_ValueType>(),
^
/home/james/git/trogdor-pp/src/core/event/triggers/luaeventtrigger.cpp:42:32: note: in instantiation of function template specialization 'std::any_cast<std::tuple<std::any> >' requested here
auto arg = std::any_cast<std::tuple<std::any>>(a);
^
In file included from /home/james/git/trogdor-pp/src/core/event/triggers/luaeventtrigger.cpp:1:
In file included from /home/james/git/trogdor-pp/src/core/include/trogdor/game.h:5:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:37:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/new:40:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/exception:144:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/nested_exception.h:40:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/move.h:55:
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:137:31: error: no member named 'value' in 'std::is_copy_constructible<std::tuple<std::any> >'
: public conditional<_B1::value, __and_<_B2, _B3, _Bn...>, _B1>::type
~~~~~^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:150:37: note: in instantiation of template class 'std::__and_<std::is_copy_constructible<std::tuple<std::any> >, std::__not_<std::is_constructible<std::tuple<std::any>, const std::tuple<std::any> &> >, std::__not_<std::__is_in_place_type<std::tuple<std::any> > > >' requested here
inline constexpr bool __and_v = __and_<_Bn...>::value;
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:192:27: note: in instantiation of variable template specialization 'std::__and_v<std::is_copy_constructible<std::tuple<std::any> >, std::__not_<std::is_constructible<std::tuple<std::any>, const std::tuple<std::any> &> >, std::__not_<std::__is_in_place_type<std::tuple<std::any> > > >' requested here
enable_if_t<__and_v<is_copy_constructible<_Tp>,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:196:7: note: while substituting prior template arguments into non-type template parameter [with _ValueType = const std::tuple<std::any> &, _Tp = std::tuple<std::any>, _Mgr = std::any::_Manager_external<std::tuple<std::any> >]
any(_ValueType&& __value)
^~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:884:56: note: while substituting deduced template arguments into function template 'any' [with _ValueType = const std::tuple<std::any> &, _Tp = (no value), _Mgr = (no value), $3 = (no value)]
: public __bool_constant<__is_constructible(_Tp, _Args...)>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:884:32: note: while substituting deduced template arguments into function template 'tuple' [with _Dummy = (no value), $1 = (no value)]
: public __bool_constant<__is_constructible(_Tp, _Args...)>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:902:14: note: (skipping 1 context in backtrace; use -ftemplate-backtrace-limit=0 to see all)
: public is_constructible<_Tp, const _Tp&>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:908:14: note: in instantiation of template class 'std::__is_copy_constructible_impl<std::tuple<std::any>, true>' requested here
: public __is_copy_constructible_impl<_Tp>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/type_traits:109:14: note: in instantiation of template class 'std::is_copy_constructible<std::tuple<std::any> >' requested here
: public conditional<_B1::value, _B1, _B2>::type
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:358:16: note: in instantiation of template class 'std::__or_<std::is_reference<std::tuple<std::any> >, std::is_copy_constructible<std::tuple<std::any> > >' requested here
{ return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/any:481:26: note: in instantiation of function template specialization 'std::any::__is_valid_cast<std::tuple<std::any> >' requested here
static_assert(any::__is_valid_cast<_ValueType>(),
^
/home/james/git/trogdor-pp/src/core/event/triggers/luaeventtrigger.cpp:42:32: note: in instantiation of function template specialization 'std::any_cast<std::tuple<std::any> >' requested here
auto arg = std::any_cast<std::tuple<std::any>>(a);我很难把所有这些都拆开，弄清楚出了什么问题，以及如何解决问题。
编辑:我们在注释中发现，这段代码不是在G++ 9和更低版本下编译的，而是在G++ 10和更高版本上编译的，在clang 10和更低版本上也会失败，但是在clang 11和更高版本上编译。有没有人对为什么会这样有任何猜测？
回答 1
Stack Overflow用户
回答已采纳
发布于 2020-12-06 04:15:05
关键部分是错误：no member named 'value' in 'std::is_copy_constructible<std::tuple<std::any> >'
这是编译器抱怨指定对象std::tuple不可复制的一种方式。
显然，你的gcc不相信std：：tuplestd：：任何东西都是可复制的.如果元组中的所有内容都是可复制的，元组本身就应该是可复制的。考虑到std::any是C++17，而gcc 9的C++17支持是不完整的，至少就C++17的这一部分而言是不完整的(gcc 11的特征列表仍然包含一些C++17功能)。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/65163455
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