use WeightedSum in GetInteractionLength

Environment/NuclearComposition.h

@@ -16,6 +16,7 @@
 #include <corsika/units/PhysicalUnits.h>
 
 #include <cassert>
+#include <functional>
 #include <numeric>
 #include <random>
 #include <stdexcept>
@@ -82,7 +83,6 @@ namespace corsika::environment {
     auto WeightedSum(TFunction func) const {
       using ResultQuantity = decltype(func(*fComponents.cbegin()));
 
-      auto const sum = [](auto x, auto y) { return x + y; };
       auto const prod = [&](auto const compID, auto const fraction) {
         return func(compID) * fraction;
       };
@@ -91,12 +91,12 @@ namespace corsika::environment {
         return std::inner_product(
             fComponents.cbegin(), fComponents.cend(), fNumberFractions.cbegin(),
             ResultQuantity::zero(), // .zero() is defined for quantity types only
-            sum, prod);
+            std::plus<ResultQuantity>(), prod);
       } else {
         return std::inner_product(
             fComponents.cbegin(), fComponents.cend(), fNumberFractions.cbegin(),
             ResultQuantity(0), // in other cases we have to use a bare 0
-            sum, prod);
+            std::plus<ResultQuantity>(), prod);
       }
     }
 

Processes/Pythia/Interaction.cc

@@ -215,26 +215,12 @@ namespace corsika::process::pythia {
       const auto mediumComposition =
           currentNode->GetModelProperties().GetNuclearComposition();
       // determine average interaction length
-      // weighted sum
-      int i = -1;
-      si::CrossSectionType weightedProdCrossSection = 0_mb;
-      // get weights of components from environment/medium
-      const auto& w = mediumComposition.GetFractions();
-      // loop over components in medium
-      for (auto const targetId : mediumComposition.GetComponents()) {
-        i++;
-        cout << "Interaction: get interaction length for target: " << targetId << endl;
-
-        auto const [productionCrossSection, elaCrossSection] =
-            GetCrossSection(corsikaBeamId, targetId, ECoM);
-        [[maybe_unused]] const auto& dummy_elaCrossSection = elaCrossSection;
-
-        cout << "Interaction: IntLength: pythia return (mb): "
-             << productionCrossSection / 1_mb << endl
-             << "Interaction: IntLength: weight : " << w[i] << endl;
-
-        weightedProdCrossSection += w[i] * productionCrossSection;
-      }
+
+      auto const weightedProdCrossSection =
+          mediumComposition.WeightedSum([=](auto vTargetID) {
+            return std::get<0>(this->GetCrossSection(corsikaBeamId, vTargetID, ECoM));
+          });
+
       cout << "Interaction: IntLength: weighted CrossSection (mb): "
            << weightedProdCrossSection / 1_mb << endl
            << "Interaction: IntLength: average mass number: "