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P0340R2 Making std::underlying_type SFINAE-friendly

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* include/std/type_traits (__underlying_type_impl): New helper to
	make underlying_type SFINAE-friendly.
	(underlying_type): Derive from __underlying_type_impl.
	* testsuite/20_util/underlying_type/requirements/typedefs-3.cc: New
	test.

From-SVN: r269168
This commit is contained in:
Jonathan Wakely 2019-02-23 21:19:00 +00:00 committed by Jonathan Wakely
parent 46d496b9d9
commit 3c26b7598c
3 changed files with 70 additions and 3 deletions
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6
libstdc++-v3/ChangeLog
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@ -1,5 +1,11 @@
2019-02-23 Jonathan Wakely <jwakely@redhat.com>
* include/std/type_traits (__underlying_type_impl): New helper to
make underlying_type SFINAE-friendly.
(underlying_type): Derive from __underlying_type_impl.
* testsuite/20_util/underlying_type/requirements/typedefs-3.cc: New
test.
PR libstdc++/89446
* include/bits/char_traits.h (__constant_char_array): Check index is
in range before dereferencing.

15
libstdc++-v3/include/std/type_traits
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@ -2176,12 +2176,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
common_type<_Tp, _Up>>::type, _Vp...>::type
{ };
template<typename _Tp, bool = is_enum<_Tp>::value>
struct __underlying_type_impl
{
using type = __underlying_type(_Tp);
};
template<typename _Tp>
struct __underlying_type_impl<_Tp, false>
{ };
/// The underlying type of an enum.
template<typename _Tp>
struct underlying_type
{
typedef __underlying_type(_Tp) type;
};
: public __underlying_type_impl<_Tp>
{ };
template<typename _Tp>
struct __declval_protector

52
libstdc++-v3/testsuite/20_util/underlying_type/requirements/typedefs-3.cc Normal file
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@ -0,0 +1,52 @@
// 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-do compile { target c++11 } }
#include <type_traits>
// Test for SFINAE-friendly underlying_type
template<typename T, typename = typename std::underlying_type<T>::type>
constexpr bool is_enum(int) { return true; }
template<typename T>
constexpr bool is_enum(...) { return false; }
void
test01()
{
enum E { };
static_assert( is_enum<E>(0), "");
static_assert( !is_enum<void>(0), "");
static_assert( !is_enum<int>(0), "");
static_assert( !is_enum<long>(0), "");
static_assert( !is_enum<int*>(0), "");
static_assert( !is_enum<int[]>(0), "");
static_assert( !is_enum<const int*>(0), "");
static_assert( !is_enum<const int&>(0), "");
static_assert( !is_enum<int()>(0), "");
static_assert( !is_enum<int(&)()>(0), "");
static_assert( !is_enum<int(*)()>(0), "");
struct S { };
static_assert( !is_enum<S>(0), "");
static_assert( !is_enum<S&>(0), "");
static_assert( !is_enum<S*>(0), "");
static_assert( !is_enum<int S::*>(0), "");
static_assert( !is_enum<int (S::*)()>(0), "");
}