[PATCH] P0646R1 Improving the Return Value of Erase-Like Algorithms I
Jonathan Wakely
jwakely@redhat.com
Wed Jul 4 20:15:00 GMT 2018
In C++2a the remove, remove_if and unique members of std::list and
std::forward_list have been changed to return the number of elements
removed. This is an ABI change for the remove members and the
non-template unique members, so an abi-tag is used to give those symbols
new mangled names in C++2a mode. For the function templates the return
type is part of the mangled name so no abi-tag is needed.
* include/bits/forward_list.h (__cpp_lib_list_remove_return_type):
Define.
(forward_list::__remove_return_type): Define typedef as size_type or
void, according to __cplusplus value.
(_GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG): Define macro as abi-tag or
empty, according to __cplusplus value.
(forward_list::remove, forward_list::unique): Use typedef and macro
to change return type and add abi-tag for C++2a.
(forward_list::remove_if<Pred>, forward_list::unique<BinPred>): Use
typedef to change return type for C++2a.
* include/bits/forward_list.tcc (_GLIBCXX20_ONLY): Define macro.
(forward_list::remove, forward_list::remove_if<Pred>)
(forward_list::unique<BinPred>): Return number of removed elements
for C++2a.
* include/bits/list.tcc (_GLIBCXX20_ONLY): Define macro.
(list::remove, list::unique, list::remove_if<Predicate>)
(list::unique<BinaryPredicate>): Return number of removed elements
for C++2a.
* include/bits/stl_list.h (__cpp_lib_list_remove_return_type): Define.
(list::__remove_return_type): Define typedef as size_type or
void, according to __cplusplus value.
(_GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG): Define macro as abi-tag or
empty, according to __cplusplus value.
(list::remove, list::unique): Use typedef and macro to change return
type and add abi-tag for C++2a.
(list::remove_if<Predicate>, list::unique<BinaryPredicate>): Use
typedef to change return type for C++2a.
* include/std/version (__cpp_lib_list_remove_return_type): Define.
* testsuite/23_containers/forward_list/operations/
remove_cxx20_return.cc: New.
* testsuite/23_containers/forward_list/operations/
unique_cxx20_return.cc: New.
Tested powerpc64le-linux, committed to trunk.
-------------- next part --------------
commit 438e6398493708d2fb13766c9dff5305ebb98eec
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Jul 4 20:13:34 2018 +0100
P0646R1 Improving the Return Value of Erase-Like Algorithms I
In C++2a the remove, remove_if and unique members of std::list and
std::forward_list have been changed to return the number of elements
removed. This is an ABI change for the remove members and the
non-template unique members, so an abi-tag is used to give those symbols
new mangled names in C++2a mode. For the function templates the return
type is part of the mangled name so no abi-tag is needed.
* include/bits/forward_list.h (__cpp_lib_list_remove_return_type):
Define.
(forward_list::__remove_return_type): Define typedef as size_type or
void, according to __cplusplus value.
(_GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG): Define macro as abi-tag or
empty, according to __cplusplus value.
(forward_list::remove, forward_list::unique): Use typedef and macro
to change return type and add abi-tag for C++2a.
(forward_list::remove_if<Pred>, forward_list::unique<BinPred>): Use
typedef to change return type for C++2a.
* include/bits/forward_list.tcc (_GLIBCXX20_ONLY): Define macro.
(forward_list::remove, forward_list::remove_if<Pred>)
(forward_list::unique<BinPred>): Return number of removed elements
for C++2a.
* include/bits/list.tcc (_GLIBCXX20_ONLY): Define macro.
(list::remove, list::unique, list::remove_if<Predicate>)
(list::unique<BinaryPredicate>): Return number of removed elements
for C++2a.
* include/bits/stl_list.h (__cpp_lib_list_remove_return_type): Define.
(list::__remove_return_type): Define typedef as size_type or
void, according to __cplusplus value.
(_GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG): Define macro as abi-tag or
empty, according to __cplusplus value.
(list::remove, list::unique): Use typedef and macro to change return
type and add abi-tag for C++2a.
(list::remove_if<Predicate>, list::unique<BinaryPredicate>): Use
typedef to change return type for C++2a.
* include/std/version (__cpp_lib_list_remove_return_type): Define.
* testsuite/23_containers/forward_list/operations/
remove_cxx20_return.cc: New.
* testsuite/23_containers/forward_list/operations/
unique_cxx20_return.cc: New.
diff --git a/libstdc++-v3/include/bits/forward_list.h b/libstdc++-v3/include/bits/forward_list.h
index 8c4c074e454..84a4ad4d5dc 100644
--- a/libstdc++-v3/include/bits/forward_list.h
+++ b/libstdc++-v3/include/bits/forward_list.h
@@ -1156,6 +1156,18 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
{ _M_splice_after(__pos, __before, __last); }
// @}
+ private:
+#if __cplusplus > 201703L
+# define __cpp_lib_list_remove_return_type 201806L
+ using __remove_return_type = size_type;
+# define _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG \
+ __attribute__((__abi_tag__("__cxx20")))
+#else
+ using __remove_return_type = void;
+# define _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
+#endif
+ public:
+
/**
* @brief Remove all elements equal to value.
* @param __val The value to remove.
@@ -1167,7 +1179,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
* touched in any way. Managing the pointer is the user's
* responsibility.
*/
- void
+ _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
+ __remove_return_type
remove(const _Tp& __val);
/**
@@ -1182,7 +1195,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
* responsibility.
*/
template<typename _Pred>
- void
+ __remove_return_type
remove_if(_Pred __pred);
/**
@@ -1195,9 +1208,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
* the pointed-to memory is not touched in any way. Managing
* the pointer is the user's responsibility.
*/
- void
+ _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
+ __remove_return_type
unique()
- { unique(std::equal_to<_Tp>()); }
+ { return unique(std::equal_to<_Tp>()); }
+
+#undef _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
/**
* @brief Remove consecutive elements satisfying a predicate.
@@ -1212,7 +1228,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
* Managing the pointer is the user's responsibility.
*/
template<typename _BinPred>
- void
+ __remove_return_type
unique(_BinPred __binary_pred);
/**
diff --git a/libstdc++-v3/include/bits/forward_list.tcc b/libstdc++-v3/include/bits/forward_list.tcc
index b41fbbb52f2..8a62a5ee748 100644
--- a/libstdc++-v3/include/bits/forward_list.tcc
+++ b/libstdc++-v3/include/bits/forward_list.tcc
@@ -278,11 +278,18 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
return iterator(const_cast<_Node_base*>(__pos._M_node));
}
+#if __cplusplus > 201703L
+# define _GLIBCXX20_ONLY(__expr) __expr
+#else
+# define _GLIBCXX20_ONLY(__expr)
+#endif
+
template<typename _Tp, typename _Alloc>
- void
+ auto
forward_list<_Tp, _Alloc>::
- remove(const _Tp& __val)
+ remove(const _Tp& __val) -> __remove_return_type
{
+ size_type __removed __attribute__((__unused__)) = 0;
_Node_base* __curr = &this->_M_impl._M_head;
_Node_base* __extra = nullptr;
@@ -293,6 +300,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
if (__tmp->_M_valptr() != std::__addressof(__val))
{
this->_M_erase_after(__curr);
+ _GLIBCXX20_ONLY( __removed++ );
continue;
}
else
@@ -302,46 +310,62 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
}
if (__extra)
- this->_M_erase_after(__extra);
+ {
+ this->_M_erase_after(__extra);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
+ return _GLIBCXX20_ONLY( __removed );
}
template<typename _Tp, typename _Alloc>
template<typename _Pred>
- void
+ auto
forward_list<_Tp, _Alloc>::
- remove_if(_Pred __pred)
+ remove_if(_Pred __pred) -> __remove_return_type
{
+ size_type __removed __attribute__((__unused__)) = 0;
_Node_base* __curr = &this->_M_impl._M_head;
while (_Node* __tmp = static_cast<_Node*>(__curr->_M_next))
{
if (__pred(*__tmp->_M_valptr()))
- this->_M_erase_after(__curr);
+ {
+ this->_M_erase_after(__curr);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
else
__curr = __curr->_M_next;
}
+ return _GLIBCXX20_ONLY( __removed );
}
template<typename _Tp, typename _Alloc>
template<typename _BinPred>
- void
+ auto
forward_list<_Tp, _Alloc>::
- unique(_BinPred __binary_pred)
+ unique(_BinPred __binary_pred) -> __remove_return_type
{
iterator __first = begin();
iterator __last = end();
if (__first == __last)
- return;
+ return _GLIBCXX20_ONLY(0);
+ size_type __removed __attribute__((__unused__)) = 0;
iterator __next = __first;
while (++__next != __last)
{
if (__binary_pred(*__first, *__next))
- erase_after(__first);
+ {
+ erase_after(__first);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
else
__first = __next;
__next = __first;
}
+ return _GLIBCXX20_ONLY( __removed );
}
+#undef _GLIBCXX20_ONLY
+
template<typename _Tp, typename _Alloc>
template<typename _Comp>
void
diff --git a/libstdc++-v3/include/bits/list.tcc b/libstdc++-v3/include/bits/list.tcc
index e90d9574cd2..cdd95527ef5 100644
--- a/libstdc++-v3/include/bits/list.tcc
+++ b/libstdc++-v3/include/bits/list.tcc
@@ -320,11 +320,18 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
insert(__last1, __first2, __last2);
}
+#if __cplusplus > 201703L
+# define _GLIBCXX20_ONLY(__expr) __expr
+#else
+# define _GLIBCXX20_ONLY(__expr)
+#endif
+
template<typename _Tp, typename _Alloc>
- void
+ typename list<_Tp, _Alloc>::__remove_return_type
list<_Tp, _Alloc>::
remove(const value_type& __value)
{
+ size_type __removed __attribute__((__unused__)) = 0;
iterator __first = begin();
iterator __last = end();
iterator __extra = __last;
@@ -338,34 +345,46 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// 526. Is it undefined if a function in the standard changes
// in parameters?
if (std::__addressof(*__first) != std::__addressof(__value))
- _M_erase(__first);
+ {
+ _M_erase(__first);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
else
__extra = __first;
}
__first = __next;
}
if (__extra != __last)
- _M_erase(__extra);
+ {
+ _M_erase(__extra);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
+ return _GLIBCXX20_ONLY( __removed );
}
template<typename _Tp, typename _Alloc>
- void
+ typename list<_Tp, _Alloc>::__remove_return_type
list<_Tp, _Alloc>::
unique()
{
iterator __first = begin();
iterator __last = end();
if (__first == __last)
- return;
+ return _GLIBCXX20_ONLY( 0 );
+ size_type __removed __attribute__((__unused__)) = 0;
iterator __next = __first;
while (++__next != __last)
{
if (*__first == *__next)
- _M_erase(__next);
+ {
+ _M_erase(__next);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
else
__first = __next;
__next = __first;
}
+ return _GLIBCXX20_ONLY( __removed );
}
template<typename _Tp, typename _Alloc>
@@ -510,10 +529,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
template<typename _Tp, typename _Alloc>
template <typename _Predicate>
- void
+ typename list<_Tp, _Alloc>::__remove_return_type
list<_Tp, _Alloc>::
remove_if(_Predicate __pred)
{
+ size_type __removed __attribute__((__unused__)) = 0;
iterator __first = begin();
iterator __last = end();
while (__first != __last)
@@ -521,32 +541,43 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
iterator __next = __first;
++__next;
if (__pred(*__first))
- _M_erase(__first);
+ {
+ _M_erase(__first);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
__first = __next;
}
+ return _GLIBCXX20_ONLY( __removed );
}
template<typename _Tp, typename _Alloc>
template <typename _BinaryPredicate>
- void
+ typename list<_Tp, _Alloc>::__remove_return_type
list<_Tp, _Alloc>::
unique(_BinaryPredicate __binary_pred)
{
iterator __first = begin();
iterator __last = end();
if (__first == __last)
- return;
+ return _GLIBCXX20_ONLY(0);
+ size_type __removed __attribute__((__unused__)) = 0;
iterator __next = __first;
while (++__next != __last)
{
if (__binary_pred(*__first, *__next))
- _M_erase(__next);
+ {
+ _M_erase(__next);
+ _GLIBCXX20_ONLY( __removed++ );
+ }
else
__first = __next;
__next = __first;
}
+ return _GLIBCXX20_ONLY( __removed );
}
+#undef _GLIBCXX20_ONLY
+
template<typename _Tp, typename _Alloc>
template <typename _StrictWeakOrdering>
void
diff --git a/libstdc++-v3/include/bits/stl_list.h b/libstdc++-v3/include/bits/stl_list.h
index 59e056df604..47749142e0e 100644
--- a/libstdc++-v3/include/bits/stl_list.h
+++ b/libstdc++-v3/include/bits/stl_list.h
@@ -1673,6 +1673,18 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
{ splice(__position, std::move(__x), __first, __last); }
#endif
+ private:
+#if __cplusplus > 201703L
+# define __cpp_lib_list_remove_return_type 201806L
+ typedef size_type __remove_return_type;
+# define _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG \
+ __attribute__((__abi_tag__("__cxx20")))
+#else
+ typedef void __remove_return_type;
+# define _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
+#endif
+ public:
+
/**
* @brief Remove all elements equal to value.
* @param __value The value to remove.
@@ -1684,7 +1696,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* touched in any way. Managing the pointer is the user's
* responsibility.
*/
- void
+ _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
+ __remove_return_type
remove(const _Tp& __value);
/**
@@ -1699,7 +1712,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* responsibility.
*/
template<typename _Predicate>
- void
+ __remove_return_type
remove_if(_Predicate);
/**
@@ -1712,7 +1725,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* the pointed-to memory is not touched in any way. Managing
* the pointer is the user's responsibility.
*/
- void
+ _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
+ __remove_return_type
unique();
/**
@@ -1728,9 +1742,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* Managing the pointer is the user's responsibility.
*/
template<typename _BinaryPredicate>
- void
+ __remove_return_type
unique(_BinaryPredicate);
+#undef _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
+
/**
* @brief Merge sorted lists.
* @param __x Sorted list to merge.
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 08036ff63f2..a70c73fd12b 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -105,6 +105,7 @@
#define __cpp_lib_is_swappable 201603
#define __cpp_lib_launder 201606
#define __cpp_lib_lcm 201606
+#define __cpp_lib_list_remove_return_type 201806L
#define __cpp_lib_logical_traits 201510
#define __cpp_lib_make_from_tuple 201606
#define __cpp_lib_map_insertion 201411
diff --git a/libstdc++-v3/testsuite/23_containers/forward_list/operations/remove_cxx20_return.cc b/libstdc++-v3/testsuite/23_containers/forward_list/operations/remove_cxx20_return.cc
new file mode 100644
index 00000000000..9b46817078e
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/forward_list/operations/remove_cxx20_return.cc
@@ -0,0 +1,66 @@
+// Copyright (C) 2018 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 run { target c++2a } }
+
+#include <forward_list>
+#include <testsuite_hooks.h>
+
+using test_type = std::forward_list<int>;
+
+void
+test01()
+{
+ test_type x{1, 2, 3, 4, 3, 2, 1};
+ static_assert(std::is_same_v<decltype(x.remove(0)), test_type::size_type>);
+ test_type::size_type r = x.remove(0);
+ VERIFY( r == 0 );
+ r = x.remove(1);
+ VERIFY( r == 2 );
+ r = x.remove(1);
+ VERIFY( r == 0 );
+ r = x.remove(4);
+ VERIFY( r == 1 );
+}
+
+void
+test02()
+{
+ int i = 0;
+ auto pred = [&i](int val) { return val == i; };
+ test_type x{1, 2, 3, 4, 3, 2, 1};
+ static_assert(std::is_same_v<decltype(x.remove_if(pred)),
+ test_type::size_type>);
+ test_type::size_type r = x.remove_if(pred);
+ VERIFY( r == 0 );
+ i = 1;
+ r = x.remove_if(pred);
+ VERIFY( r == 2 );
+ r = x.remove_if(pred);
+ VERIFY( r == 0 );
+ i = 4;
+ r = x.remove_if(pred);
+ VERIFY( r == 1 );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
diff --git a/libstdc++-v3/testsuite/23_containers/forward_list/operations/unique_cxx20_return.cc b/libstdc++-v3/testsuite/23_containers/forward_list/operations/unique_cxx20_return.cc
new file mode 100644
index 00000000000..066330c4148
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/forward_list/operations/unique_cxx20_return.cc
@@ -0,0 +1,55 @@
+// Copyright (C) 2018 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 run { target c++2a } }
+
+#include <forward_list>
+#include <testsuite_hooks.h>
+
+using test_type = std::forward_list<int>;
+
+void
+test01()
+{
+ test_type x{1, 2, 2, 4, 4, 2, 1};
+ static_assert(std::is_same_v<decltype(x.unique()), test_type::size_type>);
+ test_type::size_type r = x.unique();
+ VERIFY( r == 2 );
+ r = x.unique();
+ VERIFY( r == 0 );
+}
+
+void
+test02()
+{
+ auto pred = [](int val, int prev) { return val == prev; };
+ test_type x{1, 2, 2, 4, 4, 2, 1};
+ static_assert(std::is_same_v<decltype(x.unique(pred)),
+ test_type::size_type>);
+ test_type::size_type r = x.unique(pred);
+ VERIFY( r == 2 );
+ r = x.unique(pred);
+ VERIFY( r == 0 );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
diff --git a/libstdc++-v3/testsuite/23_containers/list/operations/remove_cxx20_return.cc b/libstdc++-v3/testsuite/23_containers/list/operations/remove_cxx20_return.cc
new file mode 100644
index 00000000000..290646106cf
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/list/operations/remove_cxx20_return.cc
@@ -0,0 +1,66 @@
+// Copyright (C) 2018 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 run { target c++2a } }
+
+#include <list>
+#include <testsuite_hooks.h>
+
+using test_type = std::list<int>;
+
+void
+test01()
+{
+ test_type x{1, 2, 3, 4, 3, 2, 1};
+ static_assert(std::is_same_v<decltype(x.remove(0)), test_type::size_type>);
+ test_type::size_type r = x.remove(0);
+ VERIFY( r == 0 );
+ r = x.remove(1);
+ VERIFY( r == 2 );
+ r = x.remove(1);
+ VERIFY( r == 0 );
+ r = x.remove(4);
+ VERIFY( r == 1 );
+}
+
+void
+test02()
+{
+ int i = 0;
+ auto pred = [&i](int val) { return val == i; };
+ test_type x{1, 2, 3, 4, 3, 2, 1};
+ static_assert(std::is_same_v<decltype(x.remove_if(pred)),
+ test_type::size_type>);
+ test_type::size_type r = x.remove_if(pred);
+ VERIFY( r == 0 );
+ i = 1;
+ r = x.remove_if(pred);
+ VERIFY( r == 2 );
+ r = x.remove_if(pred);
+ VERIFY( r == 0 );
+ i = 4;
+ r = x.remove_if(pred);
+ VERIFY( r == 1 );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
diff --git a/libstdc++-v3/testsuite/23_containers/list/operations/unique_cxx20_return.cc b/libstdc++-v3/testsuite/23_containers/list/operations/unique_cxx20_return.cc
new file mode 100644
index 00000000000..90d6dd155ff
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/list/operations/unique_cxx20_return.cc
@@ -0,0 +1,55 @@
+// Copyright (C) 2018 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 run { target c++2a } }
+
+#include <list>
+#include <testsuite_hooks.h>
+
+using test_type = std::list<int>;
+
+void
+test01()
+{
+ test_type x{1, 2, 2, 4, 4, 2, 1};
+ static_assert(std::is_same_v<decltype(x.unique()), test_type::size_type>);
+ test_type::size_type r = x.unique();
+ VERIFY( r == 2 );
+ r = x.unique();
+ VERIFY( r == 0 );
+}
+
+void
+test02()
+{
+ auto pred = [](int val, int prev) { return val == prev; };
+ test_type x{1, 2, 2, 4, 4, 2, 1};
+ static_assert(std::is_same_v<decltype(x.unique(pred)),
+ test_type::size_type>);
+ test_type::size_type r = x.unique(pred);
+ VERIFY( r == 2 );
+ r = x.unique(pred);
+ VERIFY( r == 0 );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
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