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* [gcc r11-4575] libstdc++: Fix the default constructor of ranges::__detail::__box
@ 2020-10-30 16:33 Patrick Palka
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From: Patrick Palka @ 2020-10-30 16:33 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:f3ced6772e2257bdef4e6f4dbdd0bdcf34b5bb3f
commit r11-4575-gf3ced6772e2257bdef4e6f4dbdd0bdcf34b5bb3f
Author: Patrick Palka <ppalka@redhat.com>
Date: Fri Oct 30 12:33:13 2020 -0400
libstdc++: Fix the default constructor of ranges::__detail::__box
The class template semiregular-box<T> of [range.semi.wrap] is specified
to value-initialize the underlying object whenever its type is default
initializable. Our primary template for __detail::__box respects this
requirement, but the recently added partial specialization (for types
that are already semiregular) does not.
This patch fixes this issue, and additionally makes the corresponding in
place constructor explicit (as in the primary template).
libstdc++-v3/ChangeLog:
* include/std/ranges (__detail::__box): For the partial
specialization used by types that are already semiregular,
make the default constructor value-initialize the underlying
object instead of default-initializing it. Make its in place
constructor explicit.
* testsuite/std/ranges/adaptors/detail/semiregular_box.cc:
Augment test.
Diff:
---
libstdc++-v3/include/std/ranges | 4 ++--
.../testsuite/std/ranges/adaptors/detail/semiregular_box.cc | 10 ++++++++++
2 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index a3e5354848a..610083167d8 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -141,7 +141,7 @@ namespace ranges
struct __box<_Tp>
{
private:
- [[no_unique_address]] _Tp _M_value;
+ [[no_unique_address]] _Tp _M_value = _Tp();
public:
__box() = default;
@@ -160,7 +160,7 @@ namespace ranges
template<typename... _Args>
requires constructible_from<_Tp, _Args...>
- constexpr
+ constexpr explicit
__box(in_place_t, _Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
: _M_value{std::forward<_Args>(__args)...}
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/detail/semiregular_box.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/detail/semiregular_box.cc
index 392acff3eb6..748137f7e33 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/detail/semiregular_box.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/detail/semiregular_box.cc
@@ -71,3 +71,13 @@ static_assert(requires (__box<U> a) {
a.operator->();
a.has_value();
});
+
+constexpr bool
+test01()
+{
+ // Verify the default constructor value-initializes the underlying object.
+ __box<int> x;
+ __glibcxx_assert(*x == 0);
+ return true;
+}
+static_assert(test01());
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