Hider
Here is a patch already posted to libstdc++ mailing but I am
resending following libstdc++ maintainers advises to add gcc-patches
mailing list.
This patch proposal is to fix the behavior of std::pair regarding
the std::is_*_assignable meta programming functions.
As announced it is requiring a compiler patch to extend DR 1402
resolution to all defaulted methods.
2013-04-12 François Dumont <fdum...@gcc.gnu.org>
* call.c (joust): Extend DR 1402 to all defaulted methods.
This modification is mandatory so that pair& operator=(const pair&)
can be defaulted whereas leaving gcc consider the other operator= in
some situations like std::pair<int&, int>. This way, with usage of
std::enable_if on the template operator=, we can control when p1= p2 is
a valid expression resulting in a correct behavior of
std::is_copy_assignable.
For the moment I preferred to add a dg-require-normal-mode option
in the single test that fail to compile because of the compiler
modification.
Does DR 1402 resolution generalization need a Standard committee
validation first ?
2013-04-13 François Dumont <fdum...@gcc.gnu.org>
* include/bits/stl_pair.h (operator=(const pair&)): Defaulted.
(operator=(pair&&)): Likewise.
(template<> operator=(const pair&)): Add noexcept
qualification. Enable if is_assignable<T&, const U&> true for both
parameters.
(template<> operator=(pair<>&&)): Add noexcept
qualification. Enable if is_assignable<T&, U&&> true for both
parameters.
* testsuite/23_containers/unordered_set/55043.cc: Add
dg-require-normal-mode.
* testsuite/20_util/pair/is_move_assignable.cc: New.
* testsuite/20_util/pair/is_copy_assignable.cc: Likewise.
* testsuite/20_util/pair/is_assignable.cc: Likewise.
* testsuite/20_util/pair/is_nothrow_move_assignable.cc: Likewise.
* testsuite/20_util/pair/assign_neg.cc: Likewise.
* testsuite/20_util/pair/is_nothrow_copy_assignable.cc: Likewise.
* testsuite/20_util/pair/assign.cc: Likewise.
François
Index: call.c
===================================================================
--- call.c (revision 197829)
+++ call.c (working copy)
@@ -8377,19 +8377,20 @@
&& (IS_TYPE_OR_DECL_P (cand1->fn)))
return 1;
- /* Prefer a non-deleted function over an implicitly deleted move
- constructor or assignment operator. This differs slightly from the
- wording for issue 1402 (which says the move op is ignored by overload
- resolution), but this way produces better error messages. */
+ /* Prefer a non-deleted function over an implicitly deleted one. This
+ differs slightly from the wording for issue 1402 because:
+ - it is extended to all defaulted functions, not only the ones with
+ move semantic
+ - it says the op is ignored by overload resolution while we are
+ only making it a worst candidate, but this way produces better error
+ messages. */
if (TREE_CODE (cand1->fn) == FUNCTION_DECL
&& TREE_CODE (cand2->fn) == FUNCTION_DECL
&& DECL_DELETED_FN (cand1->fn) != DECL_DELETED_FN (cand2->fn))
{
- if (DECL_DELETED_FN (cand1->fn) && DECL_DEFAULTED_FN (cand1->fn)
- && move_fn_p (cand1->fn))
+ if (DECL_DELETED_FN (cand1->fn) && DECL_DEFAULTED_FN (cand1->fn))
return -1;
- if (DECL_DELETED_FN (cand2->fn) && DECL_DEFAULTED_FN (cand2->fn)
- && move_fn_p (cand2->fn))
+ if (DECL_DELETED_FN (cand2->fn) && DECL_DEFAULTED_FN (cand2->fn))
return 1;
}
Index: include/bits/stl_pair.h
===================================================================
--- include/bits/stl_pair.h (revision 197829)
+++ include/bits/stl_pair.h (working copy)
@@ -155,26 +155,18 @@
pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
pair&
- operator=(const pair& __p)
- {
- first = __p.first;
- second = __p.second;
- return *this;
- }
+ operator=(const pair&) = default;
pair&
- operator=(pair&& __p)
- noexcept(__and_<is_nothrow_move_assignable<_T1>,
- is_nothrow_move_assignable<_T2>>::value)
- {
- first = std::forward<first_type>(__p.first);
- second = std::forward<second_type>(__p.second);
- return *this;
- }
+ operator=(pair&&) = default;
template<class _U1, class _U2>
- pair&
+ typename enable_if<__and_<is_assignable<_T1&, const _U1&>,
+ is_assignable<_T2&, const _U2&>>::value,
+ pair&>::type
operator=(const pair<_U1, _U2>& __p)
+ noexcept(__and_<is_nothrow_assignable<_T1&, const _U1&>,
+ is_nothrow_assignable<_T2&, const _U2&>>::value)
{
first = __p.first;
second = __p.second;
@@ -182,8 +174,12 @@
}
template<class _U1, class _U2>
- pair&
+ typename enable_if<__and_<is_assignable<_T1&, _U1&&>,
+ is_assignable<_T2&, _U2&&>>::value,
+ pair&>::type
operator=(pair<_U1, _U2>&& __p)
+ noexcept(__and_<is_nothrow_assignable<_T1&, _U1&&>,
+ is_nothrow_assignable<_T2&, _U2&&>>::value)
{
first = std::forward<_U1>(__p.first);
second = std::forward<_U2>(__p.second);
Index: testsuite/23_containers/unordered_set/55043.cc
===================================================================
--- testsuite/23_containers/unordered_set/55043.cc (revision 197829)
+++ testsuite/23_containers/unordered_set/55043.cc (working copy)
@@ -1,5 +1,6 @@
// { dg-options "-std=gnu++0x" }
// { dg-do compile }
+// { dg-require-normal-mode "" }
// Copyright (C) 2013 Free Software Foundation, Inc.
//
Index: testsuite/20_util/pair/is_nothrow_move_assignable.cc
===================================================================
--- testsuite/20_util/pair/is_nothrow_move_assignable.cc (revision 0)
+++ testsuite/20_util/pair/is_nothrow_move_assignable.cc (revision 0)
@@ -0,0 +1,57 @@
+// { dg-do compile }
+// { dg-options "-std=c++11" }
+
+// Copyright (C) 2013 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 <type_traits>
+#include <utility>
+#include <testsuite_tr1.h>
+
+using namespace __gnu_test;
+
+typedef std::pair<int, int> pt1;
+typedef std::pair<int, double> pt2;
+typedef std::pair<NoexceptCopyAssignClass, NoexceptCopyAssignClass> pt3;
+typedef std::pair<ExceptCopyAssignClass, ExceptCopyAssignClass> pt4;
+typedef std::pair<ExceptCopyAssignClass, double> pt5;
+typedef std::pair<NoexceptCopyAssignClass, ExceptCopyAssignClass> pt6;
+typedef std::pair<const int, int> pt7;
+typedef std::pair<int, const int> pt8;
+typedef std::pair<NoexceptMoveAssignClass, NoexceptMoveAssignClass> pt9;
+typedef std::pair<ExceptMoveAssignClass, ExceptMoveAssignClass> pt10;
+typedef std::pair<ExceptMoveAssignClass, NoexceptMoveAssignClass> pt11;
+typedef std::pair<NoexceptMoveAssignClass, ExceptMoveAssignClass> pt12;
+typedef std::pair<int, int&> pt13;
+typedef std::pair<int&, int&> pt14;
+typedef std::pair<int, const int&> pt15;
+
+static_assert(std::is_nothrow_move_assignable<pt1>::value, "Error");
+static_assert(std::is_nothrow_move_assignable<pt2>::value, "Error");
+static_assert(std::is_nothrow_move_assignable<pt3>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt4>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt5>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt6>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt7>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt8>::value, "Error");
+static_assert(std::is_nothrow_move_assignable<pt9>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt10>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt11>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt12>::value, "Error");
+static_assert(std::is_nothrow_move_assignable<pt13>::value, "Error");
+static_assert(std::is_nothrow_move_assignable<pt14>::value, "Error");
+static_assert(!std::is_nothrow_move_assignable<pt15>::value, "Error");
Index: testsuite/20_util/pair/assign_neg.cc
===================================================================
--- testsuite/20_util/pair/assign_neg.cc (revision 0)
+++ testsuite/20_util/pair/assign_neg.cc (revision 0)
@@ -0,0 +1,29 @@
+// { dg-do compile }
+// { dg-options "-std=c++11" }
+
+// Copyright (C) 2013 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 <utility>
+
+void test01()
+{
+ std::pair<const int, int> p;
+ p = p; // { dg-error "use of deleted function" }
+}
+
+// { dg-error "can't use default assignment operator" "" { target *-*-* } 158 }
Index: testsuite/20_util/pair/is_nothrow_copy_assignable.cc
===================================================================
--- testsuite/20_util/pair/is_nothrow_copy_assignable.cc (revision 0)
+++ testsuite/20_util/pair/is_nothrow_copy_assignable.cc (revision 0)
@@ -0,0 +1,53 @@
+// { dg-do compile }
+// { dg-options "-std=c++11" }
+
+// Copyright (C) 2013 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 <type_traits>
+#include <utility>
+#include <testsuite_tr1.h>
+
+using namespace __gnu_test;
+
+typedef std::pair<int, int> pt1;
+typedef std::pair<int, double> pt2;
+typedef std::pair<const int, int> pt3;
+typedef std::pair<int, const int> pt4;
+typedef std::pair<int, const int>& pt5;
+typedef std::pair<NoexceptCopyAssignClass, NoexceptCopyAssignClass> pt6;
+typedef std::pair<ExceptCopyAssignClass, ExceptCopyAssignClass> pt7;
+typedef std::pair<ExceptCopyAssignClass, double> pt8;
+typedef std::pair<NoexceptCopyAssignClass, ExceptCopyAssignClass> pt9;
+typedef std::pair<int, DeletedCopyAssignClass> pt10;
+typedef std::pair<int, int&> pt11;
+typedef std::pair<int&, int&> pt12;
+typedef std::pair<int, const int&> pt13;
+
+static_assert(std::is_nothrow_copy_assignable<pt1>::value, "Error");
+static_assert(std::is_nothrow_copy_assignable<pt2>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt3>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt4>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt5>::value, "Error");
+static_assert(std::is_nothrow_copy_assignable<pt6>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt7>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt8>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt9>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt10>::value, "Error");
+static_assert(std::is_nothrow_copy_assignable<pt11>::value, "Error");
+static_assert(std::is_nothrow_copy_assignable<pt12>::value, "Error");
+static_assert(!std::is_nothrow_copy_assignable<pt13>::value, "Error");
Index: testsuite/20_util/pair/assign.cc
===================================================================
--- testsuite/20_util/pair/assign.cc (revision 0)
+++ testsuite/20_util/pair/assign.cc (revision 0)
@@ -0,0 +1,124 @@
+// { dg-options "-std=c++11" }
+
+// Copyright (C) 2013 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 <utility>
+#include <testsuite_hooks.h>
+#include <testsuite_counter_type.h>
+#include <testsuite_tr1.h>
+
+void test01()
+{
+ bool test __attribute__((unused)) = true;
+ using __gnu_test::counter_type;
+
+ typedef std::pair<int, counter_type> ptype;
+ ptype p1(0, 0);
+ ptype p2(1, 1);
+
+ counter_type::reset();
+
+ p1 = p2;
+
+ VERIFY( p1.first == 1 );
+ VERIFY( p1.second.val == 1 );
+ VERIFY( counter_type::copy_assign_count == 1 );
+}
+
+void test02()
+{
+ bool test __attribute__((unused)) = true;
+ using __gnu_test::counter_type;
+
+ typedef std::pair<int, counter_type> ptype;
+ ptype p1(0, 0);
+ ptype p2(1, 1);
+
+ counter_type::reset();
+
+ p1 = std::move(p2);
+
+ VERIFY( p1.first == 1 );
+ VERIFY( p1.second.val == 1 );
+ VERIFY( counter_type::move_assign_count == 1 );
+}
+
+void test03()
+{
+ bool test __attribute__((unused)) = true;
+
+ typedef std::pair<int&, int&> ptype;
+ int i = 0, j = 1;
+ ptype p1(i, j);
+ VERIFY( p1.first == 0 );
+ VERIFY( p1.second == 1 );
+
+ int k = 2, l = 3;
+ ptype p2(k, l);
+ VERIFY( p2.first == 2 );
+ VERIFY( p2.second == 3 );
+
+ p1 = p2;
+
+ VERIFY( p1.first == 2 );
+ VERIFY( p1.second == 3 );
+ VERIFY( p2.first == 2 );
+ VERIFY( p2.second == 3 );
+
+ VERIFY( i == 2 );
+
+ i = 0;
+ VERIFY( p1.first == 0 );
+}
+
+void test04()
+{
+ bool test __attribute__((unused)) = true;
+
+ typedef std::pair<int&, int> ptype;
+ int i = 0;
+ ptype p1(i, 1);
+ VERIFY( p1.first == 0 );
+ VERIFY( p1.second == 1 );
+
+ int j = 2;
+ ptype p2(j, 3);
+ VERIFY( p2.first == 2 );
+ VERIFY( p2.second == 3 );
+
+ p1 = p2;
+
+ VERIFY( p1.first == 2 );
+ VERIFY( p1.second == 3 );
+ VERIFY( p2.first == 2 );
+ VERIFY( p2.second == 3 );
+
+ VERIFY( i == 2 );
+
+ i = 0;
+ VERIFY( p1.first == 0 );
+}
+
+int main()
+{
+ test01();
+ test02();
+ test03();
+ test04();
+ return 0;
+}
Index: testsuite/20_util/pair/is_move_assignable.cc
===================================================================
--- testsuite/20_util/pair/is_move_assignable.cc (revision 0)
+++ testsuite/20_util/pair/is_move_assignable.cc (revision 0)
@@ -0,0 +1,59 @@
+// { dg-do compile }
+// { dg-options "-std=c++11" }
+
+// Copyright (C) 2013 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 <type_traits>
+#include <utility>
+#include <testsuite_tr1.h>
+
+using namespace __gnu_test;
+
+typedef std::pair<int, int> pt1;
+typedef std::pair<int, double> pt2;
+typedef std::pair<NoexceptCopyAssignClass, NoexceptCopyAssignClass> pt3;
+typedef std::pair<ExceptCopyAssignClass, ExceptCopyAssignClass> pt4;
+typedef std::pair<ExceptCopyAssignClass, double> pt5;
+typedef std::pair<NoexceptCopyAssignClass, ExceptCopyAssignClass> pt6;
+typedef std::pair<const int, int> pt7;
+typedef std::pair<int, const int> pt8;
+typedef std::pair<NoexceptMoveAssignClass, NoexceptMoveAssignClass> pt9;
+typedef std::pair<ExceptMoveAssignClass, ExceptMoveAssignClass> pt10;
+typedef std::pair<ExceptMoveAssignClass, double> pt11;
+typedef std::pair<DeletedMoveAssignClass, ExceptMoveAssignClass> pt12;
+typedef std::pair<DeletedMoveAssignClass, DeletedMoveAssignClass> pt13;
+typedef std::pair<ExceptMoveAssignClass, DeletedMoveAssignClass> pt14;
+typedef std::pair<int, int&> pt15;
+typedef std::pair<int, const int&> pt16;
+
+static_assert(std::is_move_assignable<pt1>::value, "Error");
+static_assert(std::is_move_assignable<pt2>::value, "Error");
+static_assert(std::is_move_assignable<pt3>::value, "Error");
+static_assert(std::is_move_assignable<pt4>::value, "Error");
+static_assert(std::is_move_assignable<pt5>::value, "Error");
+static_assert(std::is_move_assignable<pt6>::value, "Error");
+static_assert(!std::is_move_assignable<pt7>::value, "Error");
+static_assert(!std::is_move_assignable<pt8>::value, "Error");
+static_assert(std::is_move_assignable<pt9>::value, "Error");
+static_assert(std::is_move_assignable<pt10>::value, "Error");
+static_assert(std::is_move_assignable<pt11>::value, "Error");
+static_assert(!std::is_move_assignable<pt12>::value, "Error");
+static_assert(!std::is_move_assignable<pt13>::value, "Error");
+static_assert(!std::is_move_assignable<pt14>::value, "Error");
+static_assert(std::is_move_assignable<pt15>::value, "Error");
+static_assert(!std::is_move_assignable<pt16>::value, "Error");
Index: testsuite/20_util/pair/is_copy_assignable.cc
===================================================================
--- testsuite/20_util/pair/is_copy_assignable.cc (revision 0)
+++ testsuite/20_util/pair/is_copy_assignable.cc (revision 0)
@@ -0,0 +1,53 @@
+// { dg-do compile }
+// { dg-options "-std=c++11" }
+
+// Copyright (C) 2013 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 <type_traits>
+#include <utility>
+#include <testsuite_tr1.h>
+
+using namespace __gnu_test;
+
+typedef std::pair<int, int> pt1;
+typedef std::pair<int, double> pt2;
+typedef std::pair<const int, int> pt3;
+typedef std::pair<int, const int> pt4;
+typedef std::pair<int, const int>& pt5;
+typedef std::pair<NoexceptCopyAssignClass, NoexceptCopyAssignClass> pt6;
+typedef std::pair<ExceptCopyAssignClass, ExceptCopyAssignClass> pt7;
+typedef std::pair<ExceptCopyAssignClass, double> pt8;
+typedef std::pair<NoexceptCopyAssignClass, ExceptCopyAssignClass> pt9;
+typedef std::pair<int, DeletedCopyAssignClass> pt10;
+typedef std::pair<int, int&> pt11;
+typedef std::pair<int&, int&> pt12;
+typedef std::pair<int, const int&> pt13;
+
+static_assert(std::is_copy_assignable<pt1>::value, "Error");
+static_assert(std::is_copy_assignable<pt2>::value, "Error");
+static_assert(!std::is_copy_assignable<pt3>::value, "Error");
+static_assert(!std::is_copy_assignable<pt4>::value, "Error");
+static_assert(!std::is_copy_assignable<pt5>::value, "Error");
+static_assert(std::is_copy_assignable<pt6>::value, "Error");
+static_assert(std::is_copy_assignable<pt7>::value, "Error");
+static_assert(std::is_copy_assignable<pt8>::value, "Error");
+static_assert(std::is_copy_assignable<pt9>::value, "Error");
+static_assert(!std::is_copy_assignable<pt10>::value, "Error");
+static_assert(std::is_copy_assignable<pt11>::value, "Error");
+static_assert(std::is_copy_assignable<pt12>::value, "Error");
+static_assert(!std::is_copy_assignable<pt13>::value, "Error");
Index: testsuite/20_util/pair/is_assignable.cc
===================================================================
--- testsuite/20_util/pair/is_assignable.cc (revision 0)
+++ testsuite/20_util/pair/is_assignable.cc (revision 0)
@@ -0,0 +1,48 @@
+// { dg-do compile }
+// { dg-options "-std=c++11" }
+
+// Copyright (C) 2013 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 <type_traits>
+#include <utility>
+
+struct T1
+{
+};
+
+struct T2
+{
+ T2&
+ operator=(const T1&);
+};
+
+typedef std::pair<int, int> pt1;
+typedef std::pair<short, short> pt2;
+typedef std::pair<int, double> pt3;
+typedef std::pair<int, T1> pt4;
+typedef std::pair<int, T2> pt5;
+
+static_assert(std::is_assignable<pt1, pt2>::value, "Error");
+static_assert(std::is_assignable<pt2, pt1>::value, "Error");
+static_assert(std::is_assignable<pt1, pt3>::value, "Error");
+static_assert(!std::is_assignable<pt4, pt1>::value, "Error");
+static_assert(!std::is_assignable<pt1, pt4>::value, "Error");
+static_assert(std::is_assignable<pt5, pt4>::value, "Error");
+static_assert(!std::is_assignable<pt4, pt5>::value, "Error");
+
+
