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Implement LWG 3255 for std::span constructors

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Also fix the constraints on span(Container&) and span(const Container&)
constructors so that they aren't used for const spans or const arrays.

	* include/std/span (span(element_type(&)[N]))
	(span(array<value_type, N>&), span(const array<value_type, N>&)):
	Deduce array element type to allow safe const conversions (LWG 3255).
	[!_GLIBCXX_P1394] (span(Container&), span(const Container&)): Use
	remove_cv_t on arguments to __is_std_span and __is_std_array.
	* testsuite/23_containers/span/lwg3255.cc: New test.

From-SVN: r276298
This commit is contained in:
Jonathan Wakely 2019-09-30 12:52:08 +01:00 committed by Jonathan Wakely
parent 6438d29fb1
commit 582c57a17e
3 changed files with 100 additions and 21 deletions
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7
libstdc++-v3/ChangeLog
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@ -1,5 +1,12 @@
2019-09-30 Jonathan Wakely <jwakely@redhat.com>
* include/std/span (span(element_type(&)[N]))
(span(array<value_type, N>&), span(const array<value_type, N>&)):
Deduce array element type to allow safe const conversions (LWG 3255).
[!_GLIBCXX_P1394] (span(Container&), span(const Container&)): Use
remove_cv_t on arguments to __is_std_span and __is_std_array.
* testsuite/23_containers/span/lwg3255.cc: New test.
PR libstdc++/77936
* include/parallel/checkers.h (__is_sorted): Remove unused variable.

45
libstdc++-v3/include/std/span
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@ -125,6 +125,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Tp>
using __is_compatible = is_convertible<_Tp(*)[], _Type(*)[]>;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3255. span's array constructor is too strict
template<typename _Tp, size_t _ArrayExtent,
typename = enable_if_t<_Extent == dynamic_extent
|| _ArrayExtent == _Extent>>
using __is_compatible_array = __is_compatible<_Tp>;
public:
// member types
using value_type = remove_cv_t<_Type>;
@ -149,9 +156,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// constructors
template <typename _Dummy = _Type,
enable_if_t<is_same_v<_Dummy, _Type>
&& (_Extent == dynamic_extent || _Extent == 0)>* = nullptr>
template<bool _DefaultConstructible = (_Extent + 1u) <= 1u,
enable_if_t<_DefaultConstructible>* = nullptr>
constexpr
span() noexcept : _M_extent(0), _M_ptr(nullptr)
{ }
@ -159,28 +165,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr
span(const span&) noexcept = default;
template<size_t _ArrayExtent,
enable_if_t<_Extent == dynamic_extent || _ArrayExtent == _Extent>*
= nullptr>
template<typename _Tp, size_t _ArrayExtent,
typename = _Require<__is_compatible_array<_Tp, _ArrayExtent>>>
constexpr
span(element_type (&__arr)[_ArrayExtent]) noexcept
span(_Tp (&__arr)[_ArrayExtent]) noexcept
: span(static_cast<pointer>(__arr), _ArrayExtent)
{ }
template<size_t _ArrayExtent,
enable_if_t<_Extent == dynamic_extent || _ArrayExtent == _Extent>*
= nullptr>
template<typename _Tp, size_t _ArrayExtent,
typename = _Require<__is_compatible_array<_Tp, _ArrayExtent>>>
constexpr
span(array<value_type, _ArrayExtent>& __arr) noexcept
: span(__arr.data(), _ArrayExtent)
span(array<_Tp, _ArrayExtent>& __arr) noexcept
: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
{ }
template<size_t _ArrayExtent,
enable_if_t<_Extent == dynamic_extent || _ArrayExtent == _Extent>*
= nullptr>
template<typename _Tp, size_t _ArrayExtent,
typename = _Require<__is_compatible_array<_Tp, _ArrayExtent>>>
constexpr
span(const array<value_type, _ArrayExtent>& __arr) noexcept
: span(__arr.data(), _ArrayExtent)
span(const array<_Tp, _ArrayExtent>& __arr) noexcept
: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
{ }
// NOTE: when the time comes, and P1394 -
@ -271,8 +274,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
public:
template<typename _Container, typename = _Require<
bool_constant<_Extent == dynamic_extent>,
__not_<__detail::__is_std_span<_Container>>,
__not_<__detail::__is_std_array<_Container>>,
__not_<__detail::__is_std_span<remove_cv_t<_Container>>>,
__not_<__detail::__is_std_array<remove_cv_t<_Container>>>,
__not_<is_array<_Container>>,
__is_compatible_container<_Container>>>
constexpr
@ -283,8 +286,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Container, typename = _Require<
bool_constant<_Extent == dynamic_extent>,
__not_<__detail::__is_std_span<_Container>>,
__not_<__detail::__is_std_array<_Container>>,
__not_<__detail::__is_std_span<remove_cv_t<_Container>>>,
__not_<__detail::__is_std_array<remove_cv_t<_Container>>>,
__not_<is_array<_Container>>,
__is_compatible_container<const _Container>>>
constexpr

69
libstdc++-v3/testsuite/23_containers/span/lwg3255.cc Normal file
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@ -0,0 +1,69 @@
// Copyright (C) 2019 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 <span>
#include <array>
using std::span;
using std::dynamic_extent;
using std::array;
using std::is_constructible_v;
// LWG 3255 span's array constructor is too strict
// FIXME: remove '!' from next line when P0388R4 is implemented:
static_assert( ! is_constructible_v<span<const int* const>, array<int*, 2>> );
static_assert( is_constructible_v<span<const int>, array<const int, 4>> );
static_assert( is_constructible_v<span<int, 1>, int(&)[1]> );
static_assert( is_constructible_v<span<const int, 1>, int(&)[1]> );
static_assert( is_constructible_v<span<const int, 1>, const int(&)[1]> );
static_assert( is_constructible_v<span<int, 1>, array<int, 1>&> );
static_assert( is_constructible_v<span<const int, 1>, array<int, 1>&> );
static_assert( is_constructible_v<span<const int, 1>, array<const int, 1>&> );
static_assert( is_constructible_v<span<int, 1>, const array<int, 1>&> );
static_assert( is_constructible_v<span<const int, 1>, const array<int, 1>&> );
static_assert( is_constructible_v<span<const int, 1>, const array<const int, 1>&> );
static_assert( !is_constructible_v<span<int, 1>, int(&)[2]> );
static_assert( !is_constructible_v<span<const int, 1>, int(&)[2]> );
static_assert( !is_constructible_v<span<const int, 1>, const int(&)[2]> );
static_assert( !is_constructible_v<span<int, 1>, array<int, 2>&> );
static_assert( !is_constructible_v<span<const int, 1>, array<int, 2>&> );
static_assert( !is_constructible_v<span<const int, 1>, array<const int, 2>&> );
static_assert( !is_constructible_v<span<int, 1>, const array<int, 2>&> );
static_assert( !is_constructible_v<span<const int, 1>, const array<int, 2>&> );
static_assert( !is_constructible_v<span<const int, 1>, const array<const int, 2>&> );
static_assert( is_constructible_v<span<int>, int(&)[2]> );
static_assert( is_constructible_v<span<const int>, int(&)[2]> );
static_assert( is_constructible_v<span<const int>, const int(&)[2]> );
static_assert( is_constructible_v<span<int>, array<int, 2>&> );
static_assert( is_constructible_v<span<const int>, array<int, 2>&> );
static_assert( is_constructible_v<span<const int>, array<const int, 2>&> );
static_assert( is_constructible_v<span<int>, const array<int, 2>&> );
static_assert( is_constructible_v<span<const int>, const array<int, 2>&> );
static_assert( is_constructible_v<span<const int>, const array<const int, 2>&> );