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libstdc++: Correct noexcept-specifiers on span constructors

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As discussed at https://github.com/cplusplus/draft/issues/3534 two
std::span constructors specify incorrect conditions for throwing
exceptions. This patch makes those constructors have correct
noexcept-specifiers that accurately reflect what can actually throw.

	(span(ContiguousIterator, Sentinel)): Add conditional noexcept.
	* include/std/span (span(ContiguousIterator, size_type)): Change
	noexcept to be unconditionally true.
	* testsuite/23_containers/span/nothrow_cons.cc: New test.

From-SVN: r279206
This commit is contained in:
Jonathan Wakely 2019-12-10 23:50:26 +00:00 committed by Jonathan Wakely
parent a6ae300f9a
commit cff87282f4
3 changed files with 68 additions and 1 deletions
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7
libstdc++-v3/ChangeLog
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@ -1,3 +1,10 @@
2019-12-10 Jonathan Wakely <jwakely@redhat.com>
(span(ContiguousIterator, Sentinel)): Add conditional noexcept.
* include/std/span (span(ContiguousIterator, size_type)): Change
noexcept to be unconditionally true.
* testsuite/23_containers/span/nothrow_cons.cc: New test.
2019-12-10 François Dumont <fdumont@gcc.gnu.org>
* include/bits/stl_algobase.h

3
libstdc++-v3/include/std/span
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@ -210,6 +210,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
&& (!is_convertible_v<_Sentinel, size_type>)
constexpr
span(_ContiguousIterator __first, _Sentinel __last)
noexcept(noexcept(__last - __first))
: _M_extent(static_cast<size_type>(__last - __first)),
_M_ptr(std::to_address(__first))
{
@ -221,7 +222,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
requires (__is_compatible_iterator<_ContiguousIterator>::value)
constexpr
span(_ContiguousIterator __first, size_type __count)
noexcept(noexcept(std::to_address(__first)))
noexcept
: _M_extent(__count), _M_ptr(std::to_address(__first))
{ __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }

59
libstdc++-v3/testsuite/23_containers/span/nothrow_cons.cc Normal file
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@ -0,0 +1,59 @@
// 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>
using std::span;
using std::is_nothrow_constructible_v;
static_assert( is_nothrow_constructible_v<span<int>> );
static_assert( is_nothrow_constructible_v<span<int, 0>> );
static_assert( is_nothrow_constructible_v<span<int>, span<int>&> );
static_assert( is_nothrow_constructible_v<span<const int>, span<int>&> );
static_assert( is_nothrow_constructible_v<span<int>, span<int, 1>&> );
static_assert( is_nothrow_constructible_v<span<const int>, span<int, 1>&> );
static_assert( is_nothrow_constructible_v<span<int, 1>, span<int, 1>&> );
static_assert( is_nothrow_constructible_v<span<const int, 1>, span<int, 1>&> );
static_assert( is_nothrow_constructible_v<span<int>, int(&)[1]> );
static_assert( is_nothrow_constructible_v<span<int, 1>, int(&)[1]> );
static_assert( is_nothrow_constructible_v<span<int>, std::array<int, 1>&> );
static_assert( is_nothrow_constructible_v<span<int, 1>, std::array<int, 1>&> );
template<bool>
struct sentinel { int* p; };
template<bool B>
bool operator==(sentinel<B> s, int* p) noexcept { return s.p == p; }
template<bool B>
std::ptrdiff_t operator-(sentinel<B> s, int* p) noexcept(B) { return s.p - p; }
template<bool B>
std::ptrdiff_t operator-(int* p, sentinel<B> s) noexcept { return p - s.p; }
static_assert(std::sized_sentinel_for<sentinel<true>, int*>);
static_assert(std::sized_sentinel_for<sentinel<false>, int*>);
static_assert(is_nothrow_constructible_v<span<int>, int*, std::size_t>);
static_assert(is_nothrow_constructible_v<span<int>, int*, const int*>);
static_assert(is_nothrow_constructible_v<span<int>, int*, sentinel<true>>);
static_assert(!is_nothrow_constructible_v<span<int>, int*, sentinel<false>>);