[PATCH] Define std::shared_ptr::weak_type

[Jonathan Wakely]

Another tiny C++17 feature.

        * include/bits/shared_ptr.h (shared_ptr::weak_type): Define.
        * include/bits/shared_ptr_base.h (__shared_ptr::weak_type): Define.
        * testsuite/20_util/shared_ptr/cons/43820_neg.cc: Adjust dg-error.
        * testsuite/20_util/shared_ptr/requirements/weak_type.cc: New test.
        * testsuite/20_util/shared_ptr/cons/void_neg.cc: Likewise.

Tested x86_64-linux, committed to trunk



commit b52141d2180fc30622cf7c4208c949861b7e9e29
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Aug 3 19:21:31 2016 +0100

    Define std::shared_ptr::weak_type
    
        * include/bits/shared_ptr.h (shared_ptr::weak_type): Define.
        * include/bits/shared_ptr_base.h (__shared_ptr::weak_type): Define.
        * testsuite/20_util/shared_ptr/cons/43820_neg.cc: Adjust dg-error.
        * testsuite/20_util/shared_ptr/requirements/weak_type.cc: New test.
        * testsuite/20_util/shared_ptr/cons/void_neg.cc: Likewise.

diff --git a/libstdc++-v3/include/bits/shared_ptr.h 
b/libstdc++-v3/include/bits/shared_ptr.h
index 16f78f7..483c2bc 100644
--- a/libstdc++-v3/include/bits/shared_ptr.h
+++ b/libstdc++-v3/include/bits/shared_ptr.h
@@ -97,6 +97,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          = typename enable_if<is_convertible<_Ptr, _Tp*>::value>::type;
 
     public:
+
+#if __cplusplus > 201402L
+# define __cpp_lib_shared_ptr_weak_type 201606
+      using weak_type = weak_ptr<_Tp>;
+#endif
       /**
        *  @brief  Construct an empty %shared_ptr.
        *  @post   use_count()==0 && get()==0
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h 
b/libstdc++-v3/include/bits/shared_ptr_base.h
index 1474df6..93ce901 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -876,6 +876,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     public:
       typedef _Tp   element_type;
 
+#if __cplusplus > 201402L
+      using weak_type = __weak_ptr<_Tp, _Lp>;
+#endif
+
       constexpr __shared_ptr() noexcept
       : _M_ptr(0), _M_refcount()
       { }
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc 
b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc
index 395094f..1b3dc1d 100644
--- a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc
@@ -32,7 +32,7 @@ void test01()
 {
   X* px = 0;
   std::shared_ptr<X> p1(px);   // { dg-error "here" }
-  // { dg-error "incomplete" "" { target *-*-* } 889 }
+  // { dg-error "incomplete" "" { target *-*-* } 893 }
 
   std::shared_ptr<X> p9(ap());  // { dg-error "here" }
   // { dg-error "incomplete" "" { target *-*-* } 307 }
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc 
b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc
index 8843ffe..399d2f0 100644
--- a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc
@@ -25,5 +25,5 @@
 void test01()
 {
   std::shared_ptr<void> p((void*)nullptr);   // { dg-error "here" }
-  // { dg-error "incomplete" "" { target *-*-* } 888 }
+  // { dg-error "incomplete" "" { target *-*-* } 892 }
 }
diff --git 
a/libstdc++-v3/testsuite/20_util/shared_ptr/requirements/weak_type.cc 
b/libstdc++-v3/testsuite/20_util/shared_ptr/requirements/weak_type.cc
new file mode 100644
index 0000000..38f9502
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/requirements/weak_type.cc
@@ -0,0 +1,31 @@
+// 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/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile }
+
+#include <memory>
+
+using std::shared_ptr;
+using std::weak_ptr;
+using std::is_same_v;
+
+static_assert( is_same_v<shared_ptr<int>::weak_type, weak_ptr<int>> );
+static_assert( is_same_v<shared_ptr<void>::weak_type, weak_ptr<void>> );
+
+struct X { };
+static_assert( is_same_v<shared_ptr<X>::weak_type, weak_ptr<X>> );