Add hacks due to remaining issues in port

src/foam/containers/Lists/UList/UListIO.C

@@ -105,6 +105,10 @@ Foam::Ostream& Foam::operator<<(Foam::Ostream& os, const Foam::UList<T>& L)
 
         bool uniform = false;
 
+/****************** TODO port: hacks to circumvent errors in UListIO.C >>>>>>>>>>>>>>>*/
+// ALSO REQUIRES c++17 currently. roll-back required to c++11
+        if constexpr (is_inequality_comparable<T>::value)
+        {
         if (L.size() > 1 && contiguous<T>())
         {
             uniform = true;
@@ -179,6 +183,7 @@ Foam::Ostream& Foam::operator<<(Foam::Ostream& os, const Foam::UList<T>& L)
             os << nl << token::END_LIST << nl;
         }
         }
+    }
     else if (os.format() == IOstream::BINARY)
     {
         os << nl << L.size() << nl;

src/foam/db/IOstreams/SliceStreams/UListProxy.C

@@ -54,6 +54,10 @@ void Foam::UListProxy<T>::writeFirstElement
     const char* data
 ) const
 {
+/****************** TODO port: hacks to circumvent errors in UListIO.C >>>>>>>>>>>>>>>*/
+// ALSO REQUIRES c++17 currently. roll-back required to c++11
+    if constexpr (is_inequality_comparable<T>::value)
+    {
     if (data)
     {
         const T* dataT = reinterpret_cast<const T*>(data);
@@ -65,6 +69,7 @@ void Foam::UListProxy<T>::writeFirstElement
             << "Given data pointer is nullptr."
             << abort(FatalError);
     }
+    }
 }
 
 
@@ -160,6 +165,10 @@ Foam::UListProxy<T>::determineUniformity() const
     {
         uListProxyBase::uniformity u = uListProxyBase::UNIFORM;
 
+/****************** TODO port: hacks to circumvent errors in UListIO.C >>>>>>>>>>>>>>>*/
+// ALSO REQUIRES c++17 currently. roll-back required to c++11
+        if constexpr (is_inequality_comparable<T>::value)
+        {
         // Skip comparison of the first element with itself
         for (label i = 1; i < nElems; i++)
         {
@@ -169,6 +178,7 @@ Foam::UListProxy<T>::determineUniformity() const
                 break;
             }
         }
+        }
 
         return u;
     }

src/foam/db/IOstreams/SliceStreams/primitives_traits.H

@@ -108,6 +108,25 @@ struct is_vectorspace
     std::true_type
 {};
 
+/****************** TODO port: hacks to circumvent errors in UListIO.C >>>>>>>>>>>>>>>*/
+
+// IS_INEQUALITY_COMPARABLE
+// primary template
+template<typename T, typename = Void_T<>>
+struct is_inequality_comparable : std::false_type {};
+
+//partial specialization, maybe SFINAE'd away
+template<typename T>
+struct is_inequality_comparable
+<
+    T,
+    Void_T<decltype(std::declval<T>() != std::declval<T>())>
+>
+:
+    std::true_type
+{};
+
+/*<<<<<<<<<<<<<<<<<<<<< TODO port: hacks to circumvent errors in UListIO.C *************/
 
 // TODO: This should probably go somewhere else. Toward VectorSpace ecosystem?
 template<typename T>

wmake/rules/linux64Gcc/c++

@@ -5,7 +5,8 @@ c++WARN     = -Wall -Wextra -Wno-unused-parameter -Wold-style-cast -Wnon-virtual
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
 
-CC          = g++ -std=c++11 -m64
+# TODO port: return to c++11 again
+CC          = g++ -std=c++17 -m64
 
 include $(RULES)/c++$(WM_COMPILE_OPTION)