From 2fe62c846e3dfdff120ea88950a5b6ebe0695e4e Mon Sep 17 00:00:00 2001
From: Christopher Lackner <christopher.lackner@tuwien.ac.at>
Date: Wed, 21 Aug 2019 09:44:31 +0200
Subject: [PATCH] workaround for some compilers evaluating the declval in
 has_Range

---
 libsrc/core/array.hpp       | 24 ++----------------------
 libsrc/core/type_traits.hpp | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/libsrc/core/array.hpp b/libsrc/core/array.hpp
index d523d96b..dedd974e 100644
--- a/libsrc/core/array.hpp
+++ b/libsrc/core/array.hpp
@@ -59,27 +59,6 @@ namespace ngcore
   }
 
 
-  namespace detail
-  {
-
-    // Type trait to check if a class implements a 'range_type Range()' function
-    template<typename T>
-    struct has_Range
-    {
-    private:
-      template<typename T2>
-      static constexpr auto check(T2*) ->
-        std::enable_if<std::declval<T2>().Range(), std::true_type> { std::true_type(); }
-      template<typename>
-      static constexpr std::false_type check(...);
-      using type = decltype(check<T>(nullptr)); // NOLINT
-    public:
-      NGCORE_API static constexpr bool value = type::value;
-    };
-  }
-  template<typename T>
-  constexpr bool has_range = detail::has_Range<T>::value;
-
   template <typename AO>
   class AOWrapperIterator
   {
@@ -334,7 +313,8 @@ namespace ngcore
 
   template <typename T>
   auto Range(const T & x)
-    -> typename std::enable_if<!has_range<T>, decltype(Range_impl(x, std::is_integral<T>()))>::type {
+    -> typename std::enable_if<std::is_integral_v<T> || !has_range<T>,
+                               decltype(Range_impl(x, std::is_integral<T>()))>::type {
     return Range_impl(x, std::is_integral<T>());
   }
 
diff --git a/libsrc/core/type_traits.hpp b/libsrc/core/type_traits.hpp
index 3863940b..17da6253 100644
--- a/libsrc/core/type_traits.hpp
+++ b/libsrc/core/type_traits.hpp
@@ -28,6 +28,29 @@ namespace ngcore
     template<typename T>
     constexpr bool is_any_pointer = is_any_pointer_impl<T>::value;
   } // namespace detail
+
+  
+  // Type trait to check if a class implements a 'range_type Range()' function
+  namespace detail
+  {
+    template<typename T>
+    struct has_Range
+    {
+    private:
+      template<typename T2>
+      static constexpr auto check(T2*) ->
+        std::enable_if_t<!std::is_same_v<decltype(std::declval<T2>().Range()), void>, std::true_type>
+      { std::true_type(); }
+      template<typename>
+      static constexpr std::false_type check(...);
+      using type = decltype(check<T>(nullptr)); // NOLINT
+    public:
+      NGCORE_API static constexpr bool value = type::value;
+    };
+  }
+  template<typename T>
+  constexpr bool has_range = detail::has_Range<T>::value;
+
 } // namespace ngcore
 
 #endif // NETGEN_CORE_TYPE_TRAITS_HPP