除了说明符神秘地破坏编译(Clang，GCC不同意）

noexcept specifier mysteriously breaks compilation (clang, gcc disagree)

本文关键字：Clang GCC 不同意 编译 说明符      更新时间：2023-10-16

有问题的代码是

#include <functional>
#include <utility>
template <typename F>
void for_each(F&&) noexcept {}
template <typename F, typename T, typename... Us>
void for_each(F&& f, T&& v, Us&&... us) {
std::invoke(std::forward<F>(f), std::forward<T>(v));
for_each(std::forward<F>(f), std::forward<Us>(us)...);
}
void func(void*) noexcept {}
int main() {
for_each(func, nullptr);
}

它在 gcc 8 上编译，但在 clang 6 上失败，并出现以下错误：

/opt/wandbox/clang-6.0.0/include/c++/v1/type_traits:4198:19: error: invalid application of 'sizeof' to a function type
static_assert(sizeof(_Tp) > 0, "Type must be complete.");
^~~~~~~~~~~
/opt/wandbox/clang-6.0.0/include/c++/v1/type_traits:4203:15: note: in instantiation of template class 'std::__1::__check_complete<void (void *) noexcept>' requested here
: private __check_complete<_Tp>
^
/opt/wandbox/clang-6.0.0/include/c++/v1/type_traits:4496:15: note: in instantiation of template class 'std::__1::__check_complete<void (&)(void *) noexcept>' requested here
: private __check_complete<_Fp>
^
/opt/wandbox/clang-6.0.0/include/c++/v1/type_traits:4559:9: note: in instantiation of template class 'std::__1::__invokable_r<void, void (&)(void *) noexcept, nullptr_t &&>' requested here
__invokable<_Fp, _Args...>::value,
^
/opt/wandbox/clang-6.0.0/include/c++/v1/type_traits:4568:14: note: in instantiation of template class 'std::__1::__invoke_of<void (&)(void *) noexcept, nullptr_t &&>' requested here
: public __invoke_of<_Fp, _Args...>
^
/opt/wandbox/clang-6.0.0/include/c++/v1/type_traits:4573:22: note: in instantiation of template class 'std::__1::result_of<void (&(nullptr_t &&))(void *) noexcept>' requested here
template <class _Tp> using result_of_t = typename result_of<_Tp>::type;
^
/opt/wandbox/clang-6.0.0/include/c++/v1/functional:2349:1: note: in instantiation of template type alias 'result_of_t' requested here
result_of_t<_Fn&&(_Args&&...)>
^
prog.cc:9:3: note: while substituting deduced template arguments into function template 'invoke' [with _Fn = void (&)(void *) noexcept, _Args = <nullptr_t>]
std::invoke(std::forward<F>(f), std::forward<T>(v));
^
prog.cc:16:3: note: in instantiation of function template specialization 'for_each<void (&)(void *) noexcept, nullptr_t>' requested here
for_each(func, nullptr);
^
1 error generated.

删除func()上的noexcept说明符

void func(void*) /* noexcept */ {}

然后编译。我不明白这个。这是编译器错误吗？

libc++ 无法处理noexcept标记的函数。当函数被noexcept并且它采用错误的部分专用化(对象而不是函数时，它的机器似乎由于某种原因而失败。

由于你不能接受函数的sizeof，所以clang正确地抱怨(gcc也会(。

解决方法是传入函数指针：

for_each(&func, nullptr);

我填写了一个错误报告，该报告已修复！ :)

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