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PR libstdc++/88802 define std::hash<nullptr_t> for C++17 

PR libstdc++/88802
	* include/bits/functional_hash.h (hash<nullptr_t>): Define
	specialization for C++17 (P0513R0, LWG 2817).
	* testsuite/20_util/hash/nullptr.cc: New test.

From-SVN: r267845
This commit is contained in:
Jonathan Wakely 2019-01-11 14:54:49 +00:00 committed by Jonathan Wakely
parent d58cb9659f
commit 17a73b3c47
3 changed files with 52 additions and 0 deletions
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5
libstdc++-v3/ChangeLog
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@ -1,5 +1,10 @@
2019-01-11 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/88802
* include/bits/functional_hash.h (hash<nullptr_t>): Define
specialization for C++17 (P0513R0, LWG 2817).
* testsuite/20_util/hash/nullptr.cc: New test.
PR libstdc++/88125
* config/abi/pre/gnu.ver (GLIBCXX_3.4.6): Remove unused duplicate
pattern for std::basic_stringbuf::str().

10
libstdc++-v3/include/bits/functional_hash.h
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@ -254,6 +254,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
operator()(long double __val) const noexcept;
};
#if __cplusplus >= 201703L
template<>
struct hash<nullptr_t> : public __hash_base<size_t, nullptr_t>
{
size_t
operator()(nullptr_t) const noexcept
{ return 0; }
};
#endif
// @} group hashes
// Hint about performance of hash functor. If not fast the hash-based

37
libstdc++-v3/testsuite/20_util/hash/nullptr.cc Normal file
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@ -0,0 +1,37 @@
// 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++17" }
// { dg-do run { target c++17 } }
#include <functional>
#include <testsuite_hooks.h>
void
test01()
{
auto h1 = std::hash<std::nullptr_t>{}(nullptr);
static_assert(std::is_same_v<decltype(h1), std::size_t>);
auto h2 = std::hash<std::nullptr_t>{}(nullptr);
VERIFY( h1 == h2 );
}
int
main()
{
test01();
}