Re: [PATCH] Implement std::to_address for C++2a

[Glen Fernandes <glen.fernandes@gmail.com>]

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(Also added a new [_neg] test)

Move static_assert for function pointers to __to_address

2017-11-28  Glen Joseph Fernandes  <glenjofe@gmail.com>

        * include/bits/ptr_traits.h (to_address): Moved static_assert.
        * testsuite/20_util/to_address/1_neg.cc: New test.


Tested x86_64-pc-linux-gnu.

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commit 0081e4be38f203a0a3d40c66cfa8b1f7b88f8e61
Author: Glen Joseph Fernandes <glenjofe@gmail.com>
Date:   Tue Nov 28 23:56:48 2017 -0500

    Move static_assert for function pointers to __to_address
    
    2017-11-28  Glen Joseph Fernandes  <glenjofe@gmail.com>
    
            * include/bits/ptr_traits.h (to_address): Moved static_assert.
            * testsuite/20_util/to_address/1_neg.cc: New test.

diff --git a/libstdc++-v3/include/bits/ptr_traits.h b/libstdc++-v3/include/bits/ptr_traits.h
index 67cc7e97a80..11a0deb9448 100644
--- a/libstdc++-v3/include/bits/ptr_traits.h
+++ b/libstdc++-v3/include/bits/ptr_traits.h
@@ -147,11 +147,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
 
   template<typename _Tp>
     constexpr _Tp*
     __to_address(_Tp* __ptr) noexcept
-    { return __ptr; }
+    {
+      static_assert(!std::is_function<_Tp>::value, "not a function pointer");
+      return __ptr;
+    }
 
 #if __cplusplus <= 201703L
   template<typename _Ptr>
     constexpr typename std::pointer_traits<_Ptr>::element_type*
     __to_address(const _Ptr& __ptr)
@@ -175,14 +178,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    * @ingroup pointer_abstractions
   */
   template<typename _Tp>
     constexpr _Tp*
     to_address(_Tp* __ptr) noexcept
-    {
-      static_assert(!std::is_function_v<_Tp>, "not a pointer to function");
-      return __ptr;
-    }
+    { return std::__to_address(__ptr); }
 
   /**
    * @brief Obtain address referenced by a pointer to an object
    * @param __ptr A pointer to an object
    * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
diff --git a/libstdc++-v3/testsuite/20_util/to_address/1_neg.cc b/libstdc++-v3/testsuite/20_util/to_address/1_neg.cc
new file mode 100644
index 00000000000..c80013aa930
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/to_address/1_neg.cc
@@ -0,0 +1,36 @@
+// Copyright (C) 2017 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 compile { target c++2a } }
+// { dg-error "not a function pointer" "" { target *-*-* } 153 }
+
+#include <memory>
+
+struct P
+{
+  using element_type = void();
+
+  element_type* operator->() const noexcept
+  { return nullptr; }
+};
+
+void test01()
+{
+  P p;
+  std::to_address(p); // { dg-error "required from here" }
+}