Replace auto with explicit type

It seems that the older c++ version was deducing auto as a
initializer_list rather than a size_t

Fixes #161

examples/tools/attrs.cc

@@ -14,15 +14,14 @@ constexpr auto DEFAULT{MakeAttrs(PopulationSize(100), GenerationLength(100),
 // Notice that this function has a different ordering than DEFAULT
 void print(
   const std::string& name,
-  const Attrs<PopulationSizeValue<size_t>, DefaultGenomeValue<std::string>,
-              GenerationLengthValue<size_t>>& args) {
+  const Attrs<PopulationSizeValue<int>, DefaultGenomeValue<std::string>,
+              GenerationLengthValue<int>>& args) {
   std::cout << name << " = " << args << std::endl;
 }
 
-void printSubset(
-  const std::string& name,
-  const Attrs<typename PopulationSize::value_t<size_t>,
-              typename GenerationLength::value_t<size_t>>& args) {
+void printSubset(const std::string& name,
+                 const Attrs<typename PopulationSize::value_t<int>,
+                             typename GenerationLength::value_t<int>>& args) {
   std::cout << name << " = " << args << std::endl;
 }
 
@@ -43,10 +42,10 @@ int main() {
     "Using Universal Constructor: ",
     {PopulationSize(1), DefaultGenome("Hello World"), GenerationLength(50)});
 
-  Attrs<typename PopulationSize::value_t<size_t>,
+  Attrs<typename PopulationSize::value_t<int>,
         typename DefaultGenome::value_t<std::string>,  // Notice that this will
                                                        // be auto-converted
-        typename GenerationLength::value_t<size_t>>
+        typename GenerationLength::value_t<int>>
     user = DEFAULT;
   // Set a single member
   user.SetDefaultGenome("ASDEDFDFSA");

source/meta/type_traits.h

@@ -451,7 +451,7 @@ namespace emp {
 
   template <typename Needle, typename Haystack,
             template <typename, typename> class... Cmp>
-  static constexpr auto variadic_index_of_v{
+  static constexpr size_t variadic_index_of_v{
     variadic_index_of<Needle, Haystack, Cmp...>::value};
 
   namespace __impl_variadics_type_traits {

source/tools/attrs.h

@@ -911,7 +911,7 @@ namespace emp {
     ///  of attributes and returns a pack containing each of those attributes.
     template <class... T>
     constexpr Attrs<std::decay_t<T>...> MakeAttrs(T&&... props) {
-      return {std::forward<T>(props)...};
+      return Attrs<std::decay_t<T>...>(std::forward<T>(props)...);
     };
 
     namespace __impl_attrs_merge {