Merge topic 'gcc_48_iterator_fixes'

83d4d4e4

 ArrayPortalToIterators now compiles with GCC-4.X
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !1934

vtkm/cont/ArrayPortalToIterators.h

@@ -15,12 +15,26 @@
 
 namespace vtkmstd
 {
-
 /// Implementation of std::void_t (C++17):
 /// Allows for specialization of class templates based on members of template
 /// parameters.
+#if defined(VTKM_GCC) && (__GNUC__ < 5)
+// Due to a defect in the wording (CWG 1558) unused parameters in alias templates
+// were not guaranteed to ensure SFINAE, and therefore would consider everything
+// to match the 'true' side. For VTK-m the only known compiler that implemented
+// this defect is GCC < 5.
+template <class... T>
+struct void_pack
+{
+  using type = void;
+};
+template <class... T>
+using void_t = typename void_pack<T...>::type;
+#else
 template <typename...>
 using void_t = void;
+#endif
+
 
 } // end namespace vtkmstd