On 14/05/2019 17:25, Jonathan Wakely wrote:
* include/bits/invoke.h (__invoke_r): Define new function implementing
the INVOKE<R> pseudo-function.
* testsuite/20_util/function_objects/invoke/1.cc: Add more tests.
* testsuite/20_util/function_objects/invoke/2.cc: New test.
Tested powerpc64le-linux, committed to trunk.
diff --git a/libstdc++-v3/include/bits/invoke.h
b/libstdc++-v3/include/bits/invoke.h
index a5278a59f0c..59e22da84d4 100644
--- a/libstdc++-v3/include/bits/invoke.h
+++ b/libstdc++-v3/include/bits/invoke.h
@@ -96,6 +96,65 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
std::forward<_Args>(__args)...);
}
+#if __cplusplus >= 201703L
+ // INVOKE<R>: Invoke a callable object and convert the result to R.
+ template<typename _Res, typename _Callable, typename... _Args>
+ constexpr enable_if_t<is_invocable_r_v<_Res, _Callable, _Args...>, _Res>
+ __invoke_r(_Callable&& __fn, _Args&&... __args)
+ noexcept(is_nothrow_invocable_r_v<_Res, _Callable, _Args...>)
+ {
+ using __result = __invoke_result<_Callable, _Args...>;
+ using __type = typename __result::type;
+ using __tag = typename __result::__invoke_type;
+ if constexpr (is_void_v<_Res>)
+ std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
+ std::forward<_Args>(__args)...);
+ else
+ return std::__invoke_impl<__type>(__tag{},
+ std::forward<_Callable>(__fn),
+ std::forward<_Args>(__args)...);
+ }
+#else // C++11
+ template<typename _Res, typename _Callable, typename... _Args>
+ using __can_invoke_as_void = __enable_if_t<
+ __and_<is_void<_Res>, __is_invocable<_Callable, _Args...>>::value,
+ _Res
+ >;
+
+ template<typename _Res, typename _Callable, typename... _Args>
+ using __can_invoke_as_nonvoid = __enable_if_t<
+ __and_<__not_<is_void<_Res>>,
+ is_convertible<typename __invoke_result<_Callable, _Args...>::type,
+ _Res>
+ >::value,
+ _Res
+ >;
+
+ // INVOKE<R>: Invoke a callable object and convert the result to R.
+ template<typename _Res, typename _Callable, typename... _Args>
+ constexpr __can_invoke_as_nonvoid<_Res, _Callable, _Args...>
+ __invoke_r(_Callable&& __fn, _Args&&... __args)
+ {
+ using __result = __invoke_result<_Callable, _Args...>;
+ using __type = typename __result::type;
+ using __tag = typename __result::__invoke_type;
+ return std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
+ std::forward<_Args>(__args)...);
+ }
+
+ // INVOKE<R> when R is cv void
+ template<typename _Res, typename _Callable, typename... _Args>
+ constexpr __can_invoke_as_void<_Res, _Callable, _Args...>
+ __invoke_r(_Callable&& __fn, _Args&&... __args)
I think this is a problem with -std=c++11 (but not -std=c++14) where
void is not yet a literal type, so this function can't be constexpr?
(I came across this with Clang -std=c++11 upon #include <memory>
producing an odd
In file included from
/home/sbergman/gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/memory:81:
In file included from
/home/sbergman/gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/bits/unique_ptr.h:37:
In file included from
/home/sbergman/gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/tuple:41:
/home/sbergman/gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/bits/invoke.h:148:5:
error: no return statement in constexpr function
__invoke_r(_Callable&& __fn, _Args&&... __args)
^
I first reduced that to a broken reproducer and misclassified it as a
Clang bug, <https://bugs.llvm.org/show_bug.cgi?id=41896> "Bogus 'error:
no return statement in constexpr function' when void return type is
'templated'". But what apparently happens is that since Clang knows
that the constexpr function must have a literal return type (which can't
be void for -std=c++11), it just issues that error whenever it comes a
constexpr function that lacks a return type.)
+ {
+ using __result = __invoke_result<_Callable, _Args...>;
+ using __type = typename __result::type;
+ using __tag = typename __result::__invoke_type;
+ std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
+ std::forward<_Args>(__args)...);
+ }
+#endif // C++11
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
