[libcxx] Create <__invoke> header that generates the __invoke and __invoke_constexpr functions.

[EricWF]

Summary

std::experimental::apply requires a constexpr implementation of INVOKE(...). Simply marking the current implementation of __invoke as constexpr will break existing code due to CWG issue #1581. For this reason we should add a separate function called __invoke_constexpr to be used where constexpr is required.

To supply two almost identical INVOKE(...) we use the <__invoke> header to generate the declarations and definitions by defining the required macros and including the <__invoke> header inline. The <__invoke> header can be included multiple times.

The macros used are:

• _LIBCPP_INVOKE_NAME: The name of the invoke function to be created.
• _LIBCPP_INVOKE_CONSTEXPR: The optional constexpr decorator for the invoke function.
• _LIBCPP_DECLARE_INVOKE: Declare the required invoke function.
• _LIBCPP_DEFINE_INVOKE: Define the required invoke function.

I chose not to generate invoke functions using macros because of the amount of code that would have to be within a macro block. It also is likely to yield bad error messages.

This patch also re-enables constexpr support for std::experimental::apply.

Also See:
https://llvm.org/bugs/show_bug.cgi?id=23141
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1581

[EricWF]

@rsmith Could you please look at the latest reproducer on the following bug (https://llvm.org/bugs/show_bug.cgi?id=23141). Is there a way to work around that code while having a constexpr __invoke?

[EricWF]

Abandoning in favor of D11329. That patch will help me fix the __invoke implementation in C++03.

include/__functional_base

 
 // __invoke
 
-// bullets 1 and 2
+#define _LIBCPP_INVOKE_CONSTEXPR
+#define _LIBCPP_INVOKE_NAME __invoke
+#define _LIBCPP_DEFINE_INVOKE
+#include <__invoke>
 
-template <class _Fp, class _A0, class ..._Args,
-            class>
-inline _LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
-    -> decltype((_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...))
-{
-    return (_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...);
-}
-
-template <class _Fp, class _A0, class ..._Args,
-            class>
-inline _LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
-    -> decltype(((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...))
-{
-    return ((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...);
-}
 
-// bullets 3 and 4
+// __invoke_constexpr
 
-template <class _Fp, class _A0,
-            class>
-inline _LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0)
-    -> decltype(_VSTD::forward<_A0>(__a0).*__f)
-{
-    return _VSTD::forward<_A0>(__a0).*__f;
-}
-
-template <class _Fp, class _A0,
-            class>
-inline _LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0)
-    -> decltype((*_VSTD::forward<_A0>(__a0)).*__f)
-{
-    return (*_VSTD::forward<_A0>(__a0)).*__f;
-}
-
-// bullet 5
-
-template <class _Fp, class ..._Args>
-inline _LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _Args&& ...__args)
-    -> decltype(_VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...))
-{
-    return _VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...);
-}
+#define _LIBCPP_INVOKE_CONSTEXPR _LIBCPP_CONSTEXPR
+#define _LIBCPP_INVOKE_NAME __invoke_constexpr
+#define _LIBCPP_DECLARE_INVOKE
+#define _LIBCPP_DEFINE_INVOKE
+#include <__invoke>
 
 template <class _Tp, class ..._Args>
 struct __invoke_return

include/__invoke

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_INVOKE_CONSTEXPR
+#error  _LIBCPP_INVOKE_CONSTEXPR must be defined
+#endif
+
+#ifndef _LIBCPP_INVOKE_NAME
+#error  _LIBCPP_INVOKE_NAME must be defined
+#endif
+
+#if !defined(_LIBCPP_DECLARE_INVOKE) && !defined(_LIBCPP_DEFINE_INVOKE)
+#error _LIBCPP_DECLARE_INVOKE or _LIBCPP_DEFINE_INVOKE must be defined \
+       before <__invoke> is included.
+#endif
+
+#ifdef _LIBCPP_DECLARE_INVOKE
+
+// __invoke forward declarations
+
+// fall back - none of the bullets
+
+template <class ..._Args>
+auto
+_LIBCPP_INVOKE_NAME (__any, _Args&& ...__args)
+    -> __nat;
+
+// bullets 1 and 2
+
+template <class _Fp, class _A0, class ..._Args,
+            class = typename enable_if
+            <
+                is_member_function_pointer<typename remove_reference<_Fp>::type>::value &&
+                is_base_of<typename remove_reference<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType>::type,
+                           typename remove_reference<_A0>::type>::value
+            >::type
+         >
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0, _Args&& ...__args)
+    -> decltype((_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...));
+
+template <class _Fp, class _A0, class ..._Args,
+            class = typename enable_if
+            <
+                is_member_function_pointer<typename remove_reference<_Fp>::type>::value &&
+                !is_base_of<typename remove_reference<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType>::type,
+                           typename remove_reference<_A0>::type>::value
+            >::type
+         >
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0, _Args&& ...__args)
+    -> decltype(((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...));
+
+// bullets 3 and 4
+
+template <class _Fp, class _A0,
+            class = typename enable_if
+            <
+                is_member_object_pointer<typename remove_reference<_Fp>::type>::value &&
+                is_base_of<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType,
+                           typename remove_reference<_A0>::type>::value
+            >::type
+         >
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0)
+    -> decltype(_VSTD::forward<_A0>(__a0).*__f);
+
+template <class _Fp, class _A0,
+            class = typename enable_if
+            <
+                is_member_object_pointer<typename remove_reference<_Fp>::type>::value &&
+                !is_base_of<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType,
+                           typename remove_reference<_A0>::type>::value
+            >::type
+         >
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0)
+    -> decltype((*_VSTD::forward<_A0>(__a0)).*__f);
+
+// bullet 5
+
+template <class _Fp, class ..._Args>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _Args&& ...__args)
+    -> decltype(_VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...));
+
+
+#endif // _LIBCPP_DECLARE_INVOKE
+
+#ifdef _LIBCPP_DEFINE_INVOKE
+
+// bullets 1 and 2
+
+template <class _Fp, class _A0, class ..._Args,
+            class>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0, _Args&& ...__args)
+    -> decltype((_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...))
+{
+    return (_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...);
+}
+
+template <class _Fp, class _A0, class ..._Args,
+            class>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0, _Args&& ...__args)
+    -> decltype(((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...))
+{
+    return ((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...);
+}
+
+// bullets 3 and 4
+
+template <class _Fp, class _A0,
+            class>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0)
+    -> decltype(_VSTD::forward<_A0>(__a0).*__f)
+{
+    return _VSTD::forward<_A0>(__a0).*__f;
+}
+
+template <class _Fp, class _A0,
+            class>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _A0&& __a0)
+    -> decltype((*_VSTD::forward<_A0>(__a0)).*__f)
+{
+    return (*_VSTD::forward<_A0>(__a0)).*__f;
+}
+
+// bullet 5
+
+template <class _Fp, class ..._Args>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_INVOKE_CONSTEXPR
+auto
+_LIBCPP_INVOKE_NAME (_Fp&& __f, _Args&& ...__args)
+    -> decltype(_VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...))
+{
+    return _VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...);
+}
+
+#endif // _LIBCPP_DEFINE_INVOKE
+
+#undef _LIBCPP_INVOKE_CONSTEXPR
+#undef _LIBCPP_INVOKE_NAME
+#undef _LIBCPP_DECLARE_INVOKE
+#undef _LIBCPP_DEFINE_INVOKE

include/experimental/tuple

 #endif
 
 template <class _Fn, class _Tuple, size_t ..._Id>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 decltype(auto) __apply_tuple_impl(_Fn && __f, _Tuple && __t,
                                   integer_sequence<size_t, _Id...>) {
-    return _VSTD::__invoke(
+    return _VSTD::__invoke_constexpr(
         _VSTD::forward<_Fn>(__f),
         _VSTD::get<_Id>(_VSTD::forward<_Tuple>(__t))...
     );
 }
 
 template <class _Fn, class _Tuple>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 decltype(auto) apply(_Fn && __f, _Tuple && __t) {
     return _VSTD_LFTS::__apply_tuple_impl(
         _VSTD::forward<_Fn>(__f), _VSTD::forward<_Tuple>(__t),

include/type_traits

 {
 };
 
-// __invoke forward declarations
-
-// fall back - none of the bullets
-
-template <class ..._Args>
-auto
-__invoke(__any, _Args&& ...__args)
-    -> __nat;
-
-// bullets 1 and 2
-
-template <class _Fp, class _A0, class ..._Args,
-            class = typename enable_if
-            <
-                is_member_function_pointer<typename remove_reference<_Fp>::type>::value &&
-                is_base_of<typename remove_reference<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType>::type,
-                           typename remove_reference<_A0>::type>::value
-            >::type
-         >
-_LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
-    -> decltype((_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...));
-
-template <class _Fp, class _A0, class ..._Args,
-            class = typename enable_if
-            <
-                is_member_function_pointer<typename remove_reference<_Fp>::type>::value &&
-                !is_base_of<typename remove_reference<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType>::type,
-                           typename remove_reference<_A0>::type>::value
-            >::type
-         >
-_LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
-    -> decltype(((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...));
-
-// bullets 3 and 4
-
-template <class _Fp, class _A0,
-            class = typename enable_if
-            <
-                is_member_object_pointer<typename remove_reference<_Fp>::type>::value &&
-                is_base_of<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType,
-                           typename remove_reference<_A0>::type>::value
-            >::type
-         >
-_LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0)
-    -> decltype(_VSTD::forward<_A0>(__a0).*__f);
-
-template <class _Fp, class _A0,
-            class = typename enable_if
-            <
-                is_member_object_pointer<typename remove_reference<_Fp>::type>::value &&
-                !is_base_of<typename __member_pointer_traits<typename remove_reference<_Fp>::type>::_ClassType,
-                           typename remove_reference<_A0>::type>::value
-            >::type
-         >
-_LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _A0&& __a0)
-    -> decltype((*_VSTD::forward<_A0>(__a0)).*__f);
-
-// bullet 5
-
-template <class _Fp, class ..._Args>
-_LIBCPP_INLINE_VISIBILITY
-auto
-__invoke(_Fp&& __f, _Args&& ...__args)
-    -> decltype(_VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...));
+#define _LIBCPP_INVOKE_CONSTEXPR
+#define _LIBCPP_INVOKE_NAME __invoke
+#define _LIBCPP_DECLARE_INVOKE
+#include <__invoke>
 
 // __invokable
 

test/std/experimental/utilities/tuple/tuple.apply/constexpr_types.pass.cpp

 
 // UNSUPPORTED: c++98, c++03, c++11
 
-// TODO(ericwf)
-// constexpr support temporarily reverted due to bug:
-// https://llvm.org/bugs/show_bug.cgi?id=23141
-// XFAIL: *
-
 // <experimental/tuple>
 
 // template <class F, class T> constexpr decltype(auto) apply(F &&, T &&)

test/std/experimental/utilities/tuple/tuple.apply/ref_qualifiers.pass.cpp

 
 int main()
 {
-// TODO(ericwf): Re-enable constexpr support
-/*
     {
         constexpr func_obj f;
         constexpr std::tuple<> tp;

         static_assert(1 == ex::apply(static_cast<func_obj const &>(f), tp), "");
         static_assert(2 == ex::apply(static_cast<func_obj const &&>(f), tp), "");
     }
-*/
     {
         func_obj f;
         std::tuple<> tp;