Work around bug in some compilers which do not expand lambda expressions across parameter packs (#1447)

Author: leekillough

src/sst/core/serialization/impl/serialize_variant.h

@@ -71,11 +71,11 @@ class serialize_impl<std::variant<Types...>>
     // single "type" template argument. This specialization matches std::index_sequence<INDEX...> representing a
     // sequence of subscripts 0, 1, 2, ..., sizeof...(Types)-1 generated by std::index_sequence_for<Types...>
     //
-    // This set_index partial specialization has a constexpr array of function pointers initialized by a list of lambda
-    // expressions, each of which takes a std::variant<Types...>& obj argument and calls obj.emplace<INDEX>() which
-    // changes the active variant of obj to the Types... entry corresponding to INDEX. The emplace<INDEX>() method is
-    // called with no constructor arguments, which means that the new active variant will be default-constructed. This
-    // changing of the active variant happens before the new variant is deserialized in-place.
+    // This set_index partial specialization has a constexpr array of function pointers, each of which takes a
+    // std::variant<Types...>& obj argument and calls obj.emplace<INDEX>() which changes the active variant of obj to
+    // the Types... entry corresponding to INDEX. The emplace<INDEX>() method is called with no constructor arguments,
+    // which means that the new active variant will be default-constructed. This changing of the active variant happens
+    // before the new variant is deserialized in-place.
     //
     // Although std::visit can invoke a function with the currently active std::variant, it relies on knowing the
     // currently active variant as returned by index(). To CHANGE the currently active variant requires an assignment
@@ -91,11 +91,17 @@ class serialize_impl<std::variant<Types...>>
     template <typename>
     struct set_index;
 
+    template <size_t INDEX>
+    static void set_index_func(std::variant<Types...>& obj)
+    {
+        obj.template emplace<INDEX>();
+    }
+
     template <size_t... INDEX>
     struct set_index<std::index_sequence<INDEX...>>
     {
         static constexpr std::array<void (*)(std::variant<Types...>& obj), sizeof...(INDEX)> array = {
-            [](std::variant<Types...>& obj) { obj.template emplace<INDEX>(); }...
+            set_index_func<INDEX>...
         };
     };