On Thu, 29 Oct 2020, Patrick Palka wrote:
> 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
> which are already semiregular) does not.
>
> This patch fixes this issue, and additionally makes the in place
> constructor explicit (as in the primary template).
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
>
> libstdc++-v3/ChangeLog:
>
> * include/std/ranges (__detail::__box): For the partial
> specialization for types that are already semiregular,
> make the default constructor value-initialize the underlying
> object instead of default-initializing it. Make the
> corresponding in place constructor explicit.
> * testsuite/std/ranges/detail/semiregular_box.cc: New test.
> ---
> libstdc++-v3/include/std/ranges | 4 +--
> .../std/ranges/detail/semiregular_box.cc | 33 +++++++++++++++++++
> 2 files changed, 35 insertions(+), 2 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/std/ranges/detail/semiregular_box.cc
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index df02b03cada..59aac326309 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 = {};
It would be more consistent with the rest of the header to do = _Tp()
instead:
Tested on x86_64-pc-linux-gnu.
-- >8 --
---
libstdc++-v3/include/std/ranges | 4 +--
.../std/ranges/detail/semiregular_box.cc | 33 +++++++++++++++++++
2 files changed, 35 insertions(+), 2 deletions(-)
create mode 100644 libstdc++-v3/testsuite/std/ranges/detail/semiregular_box.cc
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index df02b03cada..579280d16fb 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/detail/semiregular_box.cc
b/libstdc++-v3/testsuite/std/ranges/detail/semiregular_box.cc
new file mode 100644
index 00000000000..2a909d6ae50
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/detail/semiregular_box.cc
@@ -0,0 +1,33 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <ranges>
+
+using std::ranges::__detail::__box;
+
+constexpr bool
+test01()
+{
+ // Verify the default constructor value-initializes the underlying object.
+ __box<int> x;
+ __glibcxx_assert(*x == 0);
+ return true;
+}
+static_assert(test01());
--
2.29.0.rc0
