Deprecate C++03 <functional> Extensions: std::function, std::mem_fn and more

[EricWF]

Summary

This patch deprecates almost all C++03 extensions offered by <functional>. These extensions started as fallback implementations for compilers without variadic template support.
Since compiler support is no longer an issue I would like to remove these features. The end goal is to remove both <__functional_03> and <__functional_base_03> entirely.

The features this patch deprecates are:

• std::function
• std::mem_fn
• std::reference_wrapper::operator()

Although reference_wrapper is C++11 only I chose to only deprecate the variadic call operator. The rest of the class will remain as an extension.

Killing these features allows us to kill the C++03 implementation of INVOKE and it's related traits, which have a poor QoI with a large maintenance burden.

[EricWF]

Abandoning after advice from @mclow.lists

include/__config

 #  endif
 #endif  // _LIBCPP_STD_VER
 
+#if __cplusplus < 201103L
+#define _LIBCPP_CXX03_LANG
+#else
+#if defined(_LIBCPP_HAS_NO_VARIADIC_TEMPLATES) || defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
+#error Libc++ requires a feature complete C++11 compiler in C++11 or greater.
+#endif
+#endif
+
 #if _LIBCPP_STD_VER > 11
 #define _LIBCPP_DEPRECATED [[deprecated]]
 #else
-#define _LIBCPP_DEPRECATED
+#define _LIBCPP_DEPRECATED __attribute__((__deprecated__))
+#endif
+
+#ifdef _LIBCPP_CXX03_LANG
+#if __has_extension(attribute_deprecated_with_message)
+#define _LIBCPP_DEPRECATED_CXX03_EXTENSION(__msg) __attribute__((__deprecated__(__msg)))
+#else
+#define _LIBCPP_DEPRECATED_CXX03_EXTENSION(__msg) __attribute__((__deprecated__))
+#endif
+#else
+#define _LIBCPP_DEPRECATED_CXX03_EXTENSION(__msg)
 #endif
 
 #if _LIBCPP_STD_VER <= 11

 #define _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK
 #endif
 
-#if __cplusplus < 201103L
-#define _LIBCPP_CXX03_LANG
-#else
-#if defined(_LIBCPP_HAS_NO_VARIADIC_TEMPLATES) || defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
-#error Libc++ requires a feature complete C++11 compiler in C++11 or greater.
-#endif
-#endif
 
 #if (defined(_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS) && defined(__clang__) \
       && __has_attribute(acquire_capability))

include/__functional_03

 }  // __function
 
 template<class _Rp>
-class _LIBCPP_TYPE_VIS_ONLY function<_Rp()>
+class _LIBCPP_TYPE_VIS_ONLY
+      _LIBCPP_DEPRECATED_CXX03_EXTENSION("std::function requires C++11 or newer")
+  function<_Rp()>
 {
     typedef __function::__base<_Rp()> __base;
     aligned_storage<3*sizeof(void*)>::type __buf_;

 #endif  // _LIBCPP_NO_RTTI
 
 template<class _Rp, class _A0>
-class _LIBCPP_TYPE_VIS_ONLY function<_Rp(_A0)>
+class _LIBCPP_TYPE_VIS_ONLY
+      _LIBCPP_DEPRECATED_CXX03_EXTENSION("std::function requires C++11 or newer")
+  function<_Rp(_A0)>
     : public unary_function<_A0, _Rp>
 {
     typedef __function::__base<_Rp(_A0)> __base;

 #endif  // _LIBCPP_NO_RTTI
 
 template<class _Rp, class _A0, class _A1>
-class _LIBCPP_TYPE_VIS_ONLY function<_Rp(_A0, _A1)>
+class _LIBCPP_TYPE_VIS_ONLY
+      _LIBCPP_DEPRECATED_CXX03_EXTENSION("std::function requires C++11 or newer")
+  function<_Rp(_A0, _A1)>
     : public binary_function<_A0, _A1, _Rp>
 {
     typedef __function::__base<_Rp(_A0, _A1)> __base;

 #endif  // _LIBCPP_NO_RTTI
 
 template<class _Rp, class _A0, class _A1, class _A2>
-class _LIBCPP_TYPE_VIS_ONLY function<_Rp(_A0, _A1, _A2)>
+class _LIBCPP_TYPE_VIS_ONLY
+      _LIBCPP_DEPRECATED_CXX03_EXTENSION("std::function requires C++11 or newer")
+  function<_Rp(_A0, _A1, _A2)>
 {
     typedef __function::__base<_Rp(_A0, _A1, _A2)> __base;
     aligned_storage<3*sizeof(void*)>::type __buf_;

include/__functional_base

 };
 
 template <class _Tp>
-class _LIBCPP_TYPE_VIS_ONLY reference_wrapper
+class _LIBCPP_TYPE_VIS_ONLY
+  reference_wrapper
     : public __weak_result_type<_Tp>
 {
 public:

         return __invoke(get(), _VSTD::forward<_ArgTypes>(__args)...);
     }
 #else
-
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return<type>::type
     operator() () const {
         return __invoke(get());

 
     template <class _A0>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return0<type, _A0>::type
     operator() (_A0& __a0) const {
         return __invoke(get(), __a0);

 
     template <class _A0>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return0<type, _A0 const>::type
     operator() (_A0 const& __a0) const {
         return __invoke(get(), __a0);

 
     template <class _A0, class _A1>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return1<type, _A0, _A1>::type
     operator() (_A0& __a0, _A1& __a1) const {
         return __invoke(get(), __a0, __a1);

 
     template <class _A0, class _A1>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return1<type, _A0 const, _A1>::type
     operator() (_A0 const& __a0, _A1& __a1) const {
         return __invoke(get(), __a0, __a1);

 
     template <class _A0, class _A1>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return1<type, _A0, _A1 const>::type
     operator() (_A0& __a0, _A1 const& __a1) const {
         return __invoke(get(), __a0, __a1);

 
     template <class _A0, class _A1>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return1<type, _A0 const, _A1 const>::type
     operator() (_A0 const& __a0, _A1 const& __a1) const {
         return __invoke(get(), __a0, __a1);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0, _A1, _A2>::type
     operator() (_A0& __a0, _A1& __a1, _A2& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0 const, _A1, _A2>::type
     operator() (_A0 const& __a0, _A1& __a1, _A2& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0, _A1 const, _A2>::type
     operator() (_A0& __a0, _A1 const& __a1, _A2& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0, _A1, _A2 const>::type
     operator() (_A0& __a0, _A1& __a1, _A2 const& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0 const, _A1 const, _A2>::type
     operator() (_A0 const& __a0, _A1 const& __a1, _A2& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0 const, _A1, _A2 const>::type
     operator() (_A0 const& __a0, _A1& __a1, _A2 const& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0, _A1 const, _A2 const>::type
     operator() (_A0& __a0, _A1 const& __a1, _A2 const& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

 
     template <class _A0, class _A1, class _A2>
     _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_DEPRECATED_CXX03_EXTENSION("invoking reference_wrapper requires C++11 or newer")
     typename __invoke_return2<type, _A0 const, _A1 const, _A2 const>::type
     operator() (_A0 const& __a0, _A1 const& __a1, _A2 const& __a2) const {
         return __invoke(get(), __a0, __a1, __a2);

include/functional

 
 template<class _Rp, class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY
+_LIBCPP_DEPRECATED_CXX03_EXTENSION("std::mem_fn requires C++11 or newer")
 __mem_fn<_Rp _Tp::*>
 mem_fn(_Rp _Tp::* __pm) _NOEXCEPT
 {