work around erroneous "undefined in device code" error in basic_any

cudax/include/cuda/experimental/__utility/basic_any/virtcall.cuh

@@ -22,6 +22,7 @@
 #endif // no system header
 
 #include <cuda/std/__concepts/concept_macros.h>
+#include <cuda/std/__type_traits/is_callable.h>
 
 #include <cuda/experimental/__utility/basic_any/access.cuh>
 #include <cuda/experimental/__utility/basic_any/basic_any_from.cuh>
@@ -60,35 +61,37 @@ namespace cuda::experimental
 //! except for the virtuals map, which substitutes the correct member function
 //! pointer for the user so they don't have to think about it.
 template <auto _Mbr, auto _BoundMbr>
-struct __virtuals_map_pair
+struct __virtuals_map_element
 {
   // map ifoo<>::meow to itself
-  _CCCL_NODISCARD _CUDAX_TRIVIAL_HOST_API constexpr auto operator()(__ctag<_Mbr>) const noexcept
-  {
-    return _Mbr;
-  }
+  auto operator()(__ctag<_Mbr>) const -> __virtual_fn<_Mbr>;
 
   // map ifoo<_Super>::meow to ifoo<>::meow
-  _CCCL_NODISCARD _CUDAX_TRIVIAL_HOST_API constexpr auto operator()(__ctag<_BoundMbr>) const noexcept
-  {
-    return _Mbr;
-  }
+  auto operator()(__ctag<_BoundMbr>) const -> __virtual_fn<_Mbr>;
 };
 
 template <class, class>
 struct __virtuals_map;
 
 template <class _Interface, auto... _Mbrs, class _BoundInterface, auto... _BoundMbrs>
 struct __virtuals_map<overrides_for<_Interface, _Mbrs...>, overrides_for<_BoundInterface, _BoundMbrs...>>
-    : __virtuals_map_pair<_Mbrs, _BoundMbrs>...
+    : __virtuals_map_element<_Mbrs, _BoundMbrs>...
 {
-  using __virtuals_map_pair<_Mbrs, _BoundMbrs>::operator()...;
+  using __virtuals_map_element<_Mbrs, _BoundMbrs>::operator()...;
 };
 
 template <class _Interface, class _Super>
 using __virtuals_map_for _CCCL_NODEBUG_ALIAS =
   __virtuals_map<__overrides_for<_Interface>, __overrides_for<__rebind_interface<_Interface, _Super>>>;
 
+template <auto _Mbr, class _Interface, class _Super>
+extern _CUDA_VSTD::__call_result_t<__virtuals_map_for<_Interface, _Super>, __ctag<_Mbr>> __virtual_fn_for_v;
+
+// This alias indirects through the above variable template to cache the result
+// of the virtuals map lookup.
+template <auto _Mbr, class _Interface, class _Super>
+using __virtual_fn_for _CCCL_NODEBUG_ALIAS = decltype(__virtual_fn_for_v<_Mbr, _Interface, _Super>);
+
 //!
 //! virtcall
 //!
@@ -109,8 +112,8 @@ _CUDAX_HOST_API auto __virtcall(_Self* __self, _Args&&... __args) //
   auto* __vptr = __basic_any_access::__get_vptr(*__self)->__query_interface(_Interface());
   auto* __obj  = __basic_any_access::__get_optr(*__self);
   // map the member function pointer to the correct one if necessary
-  constexpr auto _Mbr2 = __virtuals_map_for<_Interface, _Super>{}(__ctag<_Mbr>());
-  return __vptr->__virtual_fn<_Mbr2>::__fn_(__obj, static_cast<_Args&&>(__args)...);
+  using __virtual_fn_t = __virtual_fn_for<_Mbr, _Interface, _Super>;
+  return __vptr->__virtual_fn_t::__fn_(__obj, static_cast<_Args&&>(__args)...);
 }
 
 _CCCL_TEMPLATE(auto _Mbr, template <class...> class _Interface, class _Super, class... _Args)

cudax/include/cuda/experimental/__utility/basic_any/virtual_functions.cuh

@@ -64,8 +64,8 @@ _CUDAX_TRIVIAL_API auto __c_style_cast(_Src* __ptr) noexcept -> _DstPtr
 }
 
 template <class _Tp, auto _Fn, class _Ret, bool _IsConst, bool _IsNothrow, class... _Args>
-_CCCL_NODISCARD _CUDAX_API auto __override_fn_([[maybe_unused]] _CUDA_VSTD::__maybe_const<_IsConst, void>* __pv,
-                                               [[maybe_unused]] _Args... __args) noexcept(_IsNothrow) -> _Ret
+_CCCL_NODISCARD _CUDAX_HOST_API auto __override_fn_([[maybe_unused]] _CUDA_VSTD::__maybe_const<_IsConst, void>* __pv,
+                                                    [[maybe_unused]] _Args... __args) noexcept(_IsNothrow) -> _Ret
 {
   using __value_type _CCCL_NODEBUG_ALIAS = _CUDA_VSTD::__maybe_const<_IsConst, _Tp>;