ENH: add is_range test to pTraits

- helps support algorithms with list-based forwarding

src/OpenFOAM/primitives/traits/pTraits.H

@@ -41,6 +41,7 @@ Description
 
 #include "direction.H"
 #include <type_traits>  // For std::integral_constant, std::void_t (C++17)
+#include <utility>      // For declval
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -163,6 +164,31 @@ struct pTraits_has_zero
 {};
 
 
+/*---------------------------------------------------------------------------*\
+                               Container Traits
+\*---------------------------------------------------------------------------*/
+
+//- Test for containers with begin/end range iterators.
+template<class T, class = void>
+struct is_range : std::false_type {};
+
+//- Test for list containers with begin/end range iterators.
+//- \attention May yield a false positive with HashTable, HashSet etc
+template<class T>
+struct is_range
+<
+    T,
+    stdFoam::void_t
+    <
+        decltype(std::declval<T>().begin()),
+        decltype(std::declval<T>().end())
+    >
+>
+:
+    std::true_type
+{};
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace Foam