On Thu, 21 Apr 2016, Jonathan Wakely wrote:
On 20 April 2016 at 21:42, Marc Glisse wrote:
Hello,
does anyone remember why the move constructor of _Tuple_impl is not
defaulted? The attached patch does not cause any test to fail (whitespace
kept to avoid line number changes). Maybe something about tuples of
references?
I don't know/remember why. It's possible it was to workaround a
front-end bug that required it, or maybe just a mistake and it should
always have been defaulted.
Ok, then how about something like this? In order to suppress the move
constructor in tuple (when there is a non-movable element), we need to
either declare it with suitable constraints, or keep it defaulted and
ensure that we don't bypass a missing move constructor anywhere along
the way (_Tuple_impl, _Head_base). There is a strange mix of 2
strategies in the patch, I prefer the tag class, but I started using
enable_if before I realized how many places needed those horrors.
Bootstrap+regtest on powerpc64le-unknown-linux-gnu.
2016-04-22 Marc Glisse <marc.gli...@inria.fr>
* include/std/tuple (__element_arg_t): New class.
(_Head_base(const _Head&), _Tuple_impl(const _Head&, const _Tail&...):
Remove.
(_Head_base(_UHead&&)): Add __element_arg_t argument...
(_Tuple_impl): ... and adjust callers.
(_Tuple_impl(_Tuple_impl&&)): Default.
(_Tuple_impl(const _Tuple_impl<other>&),
_Tuple_impl(_Tuple_impl<other>&&), _Tuple_impl(_UHead&&): Constrain.
* testsuite/20_util/tuple/nomove.cc: New.
--
Marc GlisseIndex: libstdc++-v3/include/std/tuple
===================================================================
--- libstdc++-v3/include/std/tuple (revision 235346)
+++ libstdc++-v3/include/std/tuple (working copy)
@@ -41,38 +41,37 @@
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @addtogroup utilities
* @{
*/
+ struct __element_arg_t { };
+
template<std::size_t _Idx, typename _Head, bool _IsEmptyNotFinal>
struct _Head_base;
template<std::size_t _Idx, typename _Head>
struct _Head_base<_Idx, _Head, true>
: public _Head
{
constexpr _Head_base()
: _Head() { }
- constexpr _Head_base(const _Head& __h)
- : _Head(__h) { }
-
constexpr _Head_base(const _Head_base&) = default;
constexpr _Head_base(_Head_base&&) = default;
template<typename _UHead>
- constexpr _Head_base(_UHead&& __h)
+ constexpr _Head_base(__element_arg_t, _UHead&& __h)
: _Head(std::forward<_UHead>(__h)) { }
_Head_base(allocator_arg_t, __uses_alloc0)
: _Head() { }
template<typename _Alloc>
_Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
: _Head(allocator_arg, *__a._M_a) { }
template<typename _Alloc>
@@ -97,28 +96,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
static constexpr const _Head&
_M_head(const _Head_base& __b) noexcept { return __b; }
};
template<std::size_t _Idx, typename _Head>
struct _Head_base<_Idx, _Head, false>
{
constexpr _Head_base()
: _M_head_impl() { }
- constexpr _Head_base(const _Head& __h)
- : _M_head_impl(__h) { }
-
constexpr _Head_base(const _Head_base&) = default;
constexpr _Head_base(_Head_base&&) = default;
template<typename _UHead>
- constexpr _Head_base(_UHead&& __h)
+ constexpr _Head_base(__element_arg_t, _UHead&& __h)
: _M_head_impl(std::forward<_UHead>(__h)) { }
_Head_base(allocator_arg_t, __uses_alloc0)
: _M_head_impl() { }
template<typename _Alloc>
_Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
: _M_head_impl(allocator_arg, *__a._M_a) { }
template<typename _Alloc>
@@ -194,50 +190,49 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
static constexpr _Inherited&
_M_tail(_Tuple_impl& __t) noexcept { return __t; }
static constexpr const _Inherited&
_M_tail(const _Tuple_impl& __t) noexcept { return __t; }
constexpr _Tuple_impl()
: _Inherited(), _Base() { }
- explicit
- constexpr _Tuple_impl(const _Head& __head, const _Tail&... __tail)
- : _Inherited(__tail...), _Base(__head) { }
-
template<typename _UHead, typename... _UTail, typename = typename
enable_if<sizeof...(_Tail) == sizeof...(_UTail)>::type>
explicit
constexpr _Tuple_impl(_UHead&& __head, _UTail&&... __tail)
: _Inherited(std::forward<_UTail>(__tail)...),
- _Base(std::forward<_UHead>(__head)) { }
+ _Base(__element_arg_t(), std::forward<_UHead>(__head)) { }
constexpr _Tuple_impl(const _Tuple_impl&) = default;
+ constexpr _Tuple_impl(_Tuple_impl&&) = default;
- constexpr
- _Tuple_impl(_Tuple_impl&& __in)
- noexcept(__and_<is_nothrow_move_constructible<_Head>,
- is_nothrow_move_constructible<_Inherited>>::value)
- : _Inherited(std::move(_M_tail(__in))),
- _Base(std::forward<_Head>(_M_head(__in))) { }
-
- template<typename... _UElements>
+ template<typename... _UElements,
+ typename enable_if<
+ !is_same<_Tuple_impl,
+ _Tuple_impl<_Idx, _UElements...>>::value,
+ bool>::type = false>
constexpr _Tuple_impl(const _Tuple_impl<_Idx, _UElements...>& __in)
: _Inherited(_Tuple_impl<_Idx, _UElements...>::_M_tail(__in)),
- _Base(_Tuple_impl<_Idx, _UElements...>::_M_head(__in)) { }
+ _Base(__element_arg_t(),
+ _Tuple_impl<_Idx, _UElements...>::_M_head(__in)) { }
- template<typename _UHead, typename... _UTails>
+ template<typename _UHead, typename... _UTails,
+ typename enable_if<
+ !is_same<_Tuple_impl,
+ _Tuple_impl<_Idx, _UHead, _UTails...>>::value,
+ bool>::type = false>
constexpr _Tuple_impl(_Tuple_impl<_Idx, _UHead, _UTails...>&& __in)
: _Inherited(std::move
(_Tuple_impl<_Idx, _UHead, _UTails...>::_M_tail(__in))),
- _Base(std::forward<_UHead>
+ _Base(__element_arg_t(), std::forward<_UHead>
(_Tuple_impl<_Idx, _UHead, _UTails...>::_M_head(__in))) { }
template<typename _Alloc>
_Tuple_impl(allocator_arg_t __tag, const _Alloc& __a)
: _Inherited(__tag, __a),
_Base(__tag, __use_alloc<_Head>(__a)) { }
template<typename _Alloc>
_Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
const _Head& __head, const _Tail&... __tail)
@@ -344,43 +339,42 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
static constexpr _Head&
_M_head(_Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
static constexpr const _Head&
_M_head(const _Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
constexpr _Tuple_impl()
: _Base() { }
- explicit
- constexpr _Tuple_impl(const _Head& __head)
- : _Base(__head) { }
-
- template<typename _UHead>
+ template<typename _UHead, typename enable_if<
+ !is_same<_Tuple_impl,
+ typename remove_cv<
+ typename remove_reference<_UHead>::type>::type>::value,
+ bool>::type = false>
explicit
constexpr _Tuple_impl(_UHead&& __head)
- : _Base(std::forward<_UHead>(__head)) { }
+ : _Base(__element_arg_t(), std::forward<_UHead>(__head)) { }
constexpr _Tuple_impl(const _Tuple_impl&) = default;
+ constexpr _Tuple_impl(_Tuple_impl&&) = default;
- constexpr
- _Tuple_impl(_Tuple_impl&& __in)
- noexcept(is_nothrow_move_constructible<_Head>::value)
- : _Base(std::forward<_Head>(_M_head(__in))) { }
-
- template<typename _UHead>
+ template<typename _UHead, typename enable_if<
+ !is_same<_UHead, _Head>::value, bool>::type = false>
constexpr _Tuple_impl(const _Tuple_impl<_Idx, _UHead>& __in)
- : _Base(_Tuple_impl<_Idx, _UHead>::_M_head(__in)) { }
+ : _Base(__element_arg_t(), _Tuple_impl<_Idx, _UHead>::_M_head(__in)) { }
- template<typename _UHead>
+ template<typename _UHead, typename enable_if<
+ !is_same<_UHead, _Head>::value, bool>::type = false>
constexpr _Tuple_impl(_Tuple_impl<_Idx, _UHead>&& __in)
- : _Base(std::forward<_UHead>(_Tuple_impl<_Idx, _UHead>::_M_head(__in)))
+ : _Base(__element_arg_t(),
+ std::forward<_UHead>(_Tuple_impl<_Idx, _UHead>::_M_head(__in)))
{ }
template<typename _Alloc>
_Tuple_impl(allocator_arg_t __tag, const _Alloc& __a)
: _Base(__tag, __use_alloc<_Head>(__a)) { }
template<typename _Alloc>
_Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
const _Head& __head)
: _Base(__use_alloc<_Head, _Alloc, _Head>(__a), __head) { }
Index: libstdc++-v3/testsuite/20_util/tuple/nomove.cc
===================================================================
--- libstdc++-v3/testsuite/20_util/tuple/nomove.cc (revision 0)
+++ libstdc++-v3/testsuite/20_util/tuple/nomove.cc (working copy)
@@ -0,0 +1,39 @@
+// { dg-do compile }
+// { dg-options "-std=gnu++11" }
+
+// Copyright (C) 2016 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/>.
+
+#include <tuple>
+#include <type_traits>
+
+struct A { A(A&&)=delete; };
+struct B { int i; B(B&&)=delete; };
+
+static_assert(!std::is_copy_constructible<std::tuple<A>>::value);
+static_assert(!std::is_copy_constructible<std::tuple<B>>::value);
+static_assert(!std::is_copy_constructible<std::tuple<A,int>>::value);
+static_assert(!std::is_copy_constructible<std::tuple<B,int>>::value);
+static_assert(!std::is_copy_constructible<std::tuple<int,A>>::value);
+static_assert(!std::is_copy_constructible<std::tuple<int,B>>::value);
+static_assert(!std::is_move_constructible<std::tuple<A>>::value);
+static_assert(!std::is_move_constructible<std::tuple<B>>::value);
+static_assert(!std::is_move_constructible<std::tuple<A,int>>::value);
+static_assert(!std::is_move_constructible<std::tuple<B,int>>::value);
+static_assert(!std::is_move_constructible<std::tuple<int,A>>::value);
+static_assert(!std::is_move_constructible<std::tuple<int,B>>::value);
+
