This adds indirection through a class template partial specialization
so we don't instantiate common_type<_Types...>::type unless we need
it.
PR libstdc++/79195
* include/experimental/array (__make_array_elem): New class template
and partial specialization.
(__is_reference_wrapper): Move into __make_array_elem specialization.
(make_array): Use __make_array_elem to determine element type and move
static assertion into specialization. Qualify std::forward call.
(to_array): Add exception specifiation.
* testsuite/experimental/array/make_array.cc: Test argument types
without a common type.
* testsuite/experimental/array/neg.cc: Adjust expected error message.
Tested powerpc64le-linux, committed to trunk (because it's only an
experimental TS feature).
commit 16438869aa70f6cad56c094ed26ac73dc75c3847
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Mon Jan 23 15:15:07 2017 +0000
PR libstdc++/79195 fix make_array type deduction
PR libstdc++/79195
* include/experimental/array (__make_array_elem): New class template
and partial specialization.
(__is_reference_wrapper): Move into __make_array_elem specialization.
(make_array): Use __make_array_elem to determine element type and move
static assertion into specialization. Qualify std::forward call.
(to_array): Add exception specifiation.
* testsuite/experimental/array/make_array.cc: Test argument types
without a common type.
* testsuite/experimental/array/neg.cc: Adjust expected error message.
diff --git a/libstdc++-v3/include/experimental/array
b/libstdc++-v3/include/experimental/array
index 5899486..11cb924 100644
--- a/libstdc++-v3/include/experimental/array
+++ b/libstdc++-v3/include/experimental/array
@@ -57,35 +57,40 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @{
*/
-template <typename _Up>
- struct __is_reference_wrapper : false_type
- {};
+template<typename _Dest, typename... _Types>
+ struct __make_array_elem
+ {
+ using type = _Dest;
+ };
-template <typename _Up>
- struct __is_reference_wrapper<reference_wrapper<_Up>> : true_type
- {};
+template<typename... _Types>
+ struct __make_array_elem<void, _Types...>
+ : common_type<_Types...>
+ {
+ template <typename>
+ struct __is_reference_wrapper : false_type
+ {};
+
+ template <typename _Up>
+ struct __is_reference_wrapper<reference_wrapper<_Up>> : true_type
+ {};
+
+ static_assert(!__or_<__is_reference_wrapper<decay_t<_Types>>...>::value,
+ "make_array must be used with an explicit target type when"
+ "any of the arguments is a reference_wrapper");
+ };
template <typename _Dest = void, typename... _Types>
- constexpr auto
+ constexpr
+ array<typename __make_array_elem<_Dest, _Types...>::type, sizeof...(_Types)>
make_array(_Types&&... __t)
- -> array<conditional_t<is_void_v<_Dest>,
- common_type_t<_Types...>,
- _Dest>,
- sizeof...(_Types)>
{
- static_assert(__or_<
- __not_<is_void<_Dest>>,
- __and_<__not_<__is_reference_wrapper<decay_t<_Types>>>...>>
- ::value,
- "make_array cannot be used without an explicit target type "
- "if any of the types given is a reference_wrapper");
- return {{forward<_Types>(__t)...}};
+ return {{ std::forward<_Types>(__t)... }};
}
template <typename _Tp, size_t _Nm, size_t... _Idx>
constexpr array<remove_cv_t<_Tp>, _Nm>
- __to_array(_Tp (&__a)[_Nm],
- index_sequence<_Idx...>)
+ __to_array(_Tp (&__a)[_Nm], index_sequence<_Idx...>)
{
return {{__a[_Idx]...}};
}
@@ -93,6 +98,7 @@ template <typename _Tp, size_t _Nm, size_t... _Idx>
template <typename _Tp, size_t _Nm>
constexpr array<remove_cv_t<_Tp>, _Nm>
to_array(_Tp (&__a)[_Nm])
+ noexcept(is_nothrow_constructible<remove_cv_t<_Tp>, _Tp&>::value)
{
return __to_array(__a, make_index_sequence<_Nm>{});
}
diff --git a/libstdc++-v3/testsuite/experimental/array/make_array.cc
b/libstdc++-v3/testsuite/experimental/array/make_array.cc
index 45b1920..1b7d60e 100644
--- a/libstdc++-v3/testsuite/experimental/array/make_array.cc
+++ b/libstdc++-v3/testsuite/experimental/array/make_array.cc
@@ -18,7 +18,6 @@
// <http://www.gnu.org/licenses/>.
#include <experimental/array>
-#include <functional>
struct MoveOnly
{
@@ -27,7 +26,7 @@ struct MoveOnly
MoveOnly& operator=(MoveOnly&&) = default;
};
-int main()
+void test01()
{
char x[42];
std::array<char, 42> y = std::experimental::to_array(x);
@@ -45,3 +44,13 @@ int main()
= std::experimental::make_array(1,2L, 3);
constexpr std::array<MoveOnly, 1> zzz2 =
std::experimental::make_array(MoveOnly{});
}
+
+void test02()
+{
+ // PR libstdc++/79195
+ struct A {};
+ struct B : A {};
+ struct C : A {};
+ auto arr = std::experimental::make_array<A>(B{}, C{});
+ static_assert(std::is_same<decltype(arr), std::array<A, 2>>::value, "");
+}
diff --git a/libstdc++-v3/testsuite/experimental/array/neg.cc
b/libstdc++-v3/testsuite/experimental/array/neg.cc
index 790933d..3963287 100644
--- a/libstdc++-v3/testsuite/experimental/array/neg.cc
+++ b/libstdc++-v3/testsuite/experimental/array/neg.cc
@@ -24,5 +24,5 @@ int main()
{
int dummy;
auto bad = std::experimental::make_array(std::ref(dummy));
- // { dg-error "make_array cannot be used without an explicit target type if
any of the types given is a reference_wrapper" "" { target *-*-* } 76 }
+ // { dg-error "explicit target type" "" { target *-*-* } 78 }
}
