[v3 PATCH] Implement the missing bits of LWG 2769

[Ville Voutilainen]

On 26 February 2018 at 22:52, Jonathan Wakely <jwakely@redhat.com> wrote:
> On 25/02/18 23:22 +0200, Ville Voutilainen wrote:
>>
>> Tested partially on Linux-x64, will test with the full suite on
>> Linux-PPC64.
>> Ok for trunk and the gcc-7 branch? This is theoretically a breaking change
> This template argument should be aligned with "_ValueType" on the
> previous line, not with "is_constructible".
>
> Looking at that file, I'm also wondering if we want the alias _AnyCast
> to be defined at namespace scope. It's only used in a few function
> bodies, and its name is a bit misleading.
>
> Could you just do:
>
>  using _Up = remove_cv_t<remove_reference_t<_ValueType>>;
>
> in the four functions that use it?
>
> Then I think the is_constructible specializations would fit on one line
> anyway.


Done, new patch attached.
-------------- next part --------------
diff --git a/libstdc++-v3/include/std/any b/libstdc++-v3/include/std/any
index 466b7ca..a37eb38 100644
--- a/libstdc++-v3/include/std/any
+++ b/libstdc++-v3/include/std/any
@@ -438,8 +438,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return any(in_place_type<_Tp>, __il, std::forward<_Args>(__args)...);
     }
 
-  template <typename _Tp>
-    using _AnyCast = remove_cv_t<remove_reference_t<_Tp>>;
   /**
    * @brief Access the contained object.
    *
@@ -453,9 +451,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _ValueType>
     inline _ValueType any_cast(const any& __any)
     {
+      using _Up = remove_cv_t<remove_reference_t<_ValueType>>;
       static_assert(any::__is_valid_cast<_ValueType>(),
 	  "Template argument must be a reference or CopyConstructible type");
-      auto __p = any_cast<_AnyCast<_ValueType>>(&__any);
+      static_assert(is_constructible_v<_ValueType, const _Up&>,
+	  "Template argument must be constructible from a const value.");
+      auto __p = any_cast<_Up>(&__any);
       if (__p)
 	return static_cast<_ValueType>(*__p);
       __throw_bad_any_cast();
@@ -476,37 +477,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _ValueType>
     inline _ValueType any_cast(any& __any)
     {
+      using _Up = remove_cv_t<remove_reference_t<_ValueType>>;
       static_assert(any::__is_valid_cast<_ValueType>(),
 	  "Template argument must be a reference or CopyConstructible type");
-      auto __p = any_cast<_AnyCast<_ValueType>>(&__any);
+      static_assert(is_constructible_v<_ValueType, _Up&>,
+	  "Template argument must be constructible from an lvalue.");
+      auto __p = any_cast<_Up>(&__any);
       if (__p)
 	return static_cast<_ValueType>(*__p);
       __throw_bad_any_cast();
     }
 
-  template<typename _ValueType,
-           typename enable_if<!is_move_constructible<_ValueType>::value
-                              || is_lvalue_reference<_ValueType>::value,
-                              bool>::type = true>
-    inline _ValueType any_cast(any&& __any)
-    {
-      static_assert(any::__is_valid_cast<_ValueType>(),
-	  "Template argument must be a reference or CopyConstructible type");
-      auto __p = any_cast<_AnyCast<_ValueType>>(&__any);
-      if (__p)
-	return static_cast<_ValueType>(*__p);
-      __throw_bad_any_cast();
-    }
-
-  template<typename _ValueType,
-           typename enable_if<is_move_constructible<_ValueType>::value
-                              && !is_lvalue_reference<_ValueType>::value,
-                              bool>::type = false>
+  template<typename _ValueType>
     inline _ValueType any_cast(any&& __any)
     {
+      using _Up = remove_cv_t<remove_reference_t<_ValueType>>;
       static_assert(any::__is_valid_cast<_ValueType>(),
 	  "Template argument must be a reference or CopyConstructible type");
-      auto __p = any_cast<_AnyCast<_ValueType>>(&__any);
+      static_assert(is_constructible_v<_ValueType, _Up>,
+	  "Template argument must be constructible from an rvalue.");
+      auto __p = any_cast<_Up>(&__any);
       if (__p)
 	return static_cast<_ValueType>(std::move(*__p));
       __throw_bad_any_cast();
diff --git a/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc b/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
index 45d8b63..37a24d7 100644
--- a/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
+++ b/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
@@ -95,15 +95,6 @@ void test03()
   VERIFY(move_count == 1);
   MoveEnabled&& m3 = any_cast<MoveEnabled&&>(any(m));
   VERIFY(move_count == 1);
-  struct MoveDeleted
-  {
-    MoveDeleted(MoveDeleted&&) = delete;
-    MoveDeleted() = default;
-    MoveDeleted(const MoveDeleted&) = default;
-  };
-  MoveDeleted md;
-  MoveDeleted&& md2 = any_cast<MoveDeleted>(any(std::move(md)));
-  MoveDeleted&& md3 = any_cast<MoveDeleted&&>(any(std::move(md)));
 }
 
 void test04()
diff --git a/libstdc++-v3/testsuite/20_util/any/misc/any_cast_neg.cc b/libstdc++-v3/testsuite/20_util/any/misc/any_cast_neg.cc
index 50a9a67..62d7aaa 100644
--- a/libstdc++-v3/testsuite/20_util/any/misc/any_cast_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/any/misc/any_cast_neg.cc
@@ -20,11 +20,26 @@
 
 #include <any>
 
+using std::any;
+using std::any_cast;
+
 void test01()
 {
-  using std::any;
-  using std::any_cast;
-
   const any y(1);
-  any_cast<int&>(y); // { dg-error "invalid static_cast" "" { target { *-*-* } } 460 }
+  any_cast<int&>(y); // { dg-error "invalid static_cast" "" { target { *-*-* } } 461 }
+  // { dg-error "Template argument must be constructible from a const value" "" { target { *-*-* } } 457 }
+}
+
+void test02()
+{
+  any y(1);
+  any_cast<int&&>(y);
+  // { dg-error "Template argument must be constructible from an lvalue" "" { target { *-*-* } } 483 }
+}
+
+void test03()
+{
+  any y(1);
+  any_cast<int&>(std::move(y));  // { dg-error "invalid static_cast" "" { target { *-*-* } } 501 }
+  // { dg-error "Template argument must be constructible from an rvalue" "" { target { *-*-* } } 497 }
 }