Use traits to reduce code (#65)

Author: awegrzyn

src/VariantVisitorAdd.h

@@ -7,31 +7,21 @@ namespace monitoring
 class VariantVisitorAdd : public boost::static_visitor<boost::variant<int, std::string, double, uint64_t>>
 {
 public:
-  /// Overloads operator() to avoid operating on strings
-  /// \throws MonitoringInternalException
-  double operator()(const std::string&, const std::string&) const {
-    throw MonitoringInternalException("DerivedMetrics/VariantRateVisitor", "Cannot operate on string values");
-  }
-
-  /// Calculates rate only when two arguments of the same type are passed
-  /// \return calculated rate in Hz
-  int operator()(const int& a, const int& b) const {
-    return a + b;
-  }
-
-  double operator()(const double& a, const double& b) const {
-    return a + b;
-  }
 
-  uint64_t operator()(const uint64_t& a, const uint64_t& b) const {
+  /// Overloads operator() that sums numeric values
+  template<
+    typename T,
+    typename = typename std::enable_if<std::is_arithmetic<T>::value, T>::type
+  >
+  T operator()(const T& a, const T& b) const {
     return a + b;
   }
 
   /// If arguments have different type an exception is raised
   /// \throws MonitoringInternalException
   template<typename T, typename U>
   double operator()(const T&, const U&) const {
-    throw MonitoringInternalException("DerivedMetrics/VariantRateVisitor", "Cannot operate on different types");
+    throw MonitoringInternalException("DerivedMetrics/Visitor", "Cannot operate on different or non-numeric types");
   }
 };
 

src/VariantVisitorRate.h

@@ -16,15 +16,12 @@ class VariantVisitorRate : public boost::static_visitor<boost::variant<int, std:
   VariantVisitorRate(int count) : timestampCount(count) {
   }
 
-  /// Overloads operator() to avoid operating on strings
-  /// \throws MonitoringInternalException
-  double operator()(const std::string&, const std::string&) const {
-    throw MonitoringInternalException("DerivedMetrics/VariantRateVisitor", "Cannot operate on string values");
-  }
-
   /// Calculates rate only when two arguments of the same type are passed
   /// \return calculated rate in Hz
-  template<typename T>
+  template<
+    typename T,
+    typename = typename std::enable_if<std::is_arithmetic<T>::value, T>::type
+  >
   double operator()(const T& a, const T& b) const {
     return (1000*(static_cast<double>(a) - b)) / timestampCount;
   }
@@ -33,7 +30,7 @@ class VariantVisitorRate : public boost::static_visitor<boost::variant<int, std:
   /// \throws MonitoringInternalException
   template<typename T, typename U>
   double operator()(const T&, const U&) const {
-    throw MonitoringInternalException("DerivedMetrics/VariantRateVisitor", "Cannot operate on different types");
+    throw MonitoringInternalException("DerivedMetrics/Visitor", "Cannot operate on different or non-numeric types");
   }
 };
 

test/testDerived.cxx

@@ -1,5 +1,6 @@
 #include "Monitoring/DerivedMetrics.h"
 #include "../src/Exceptions/MonitoringInternalException.h"
+#include "../src/VariantVisitorAdd.h"
 #include <chrono>
 #include <thread>
 #include <vector>
@@ -142,6 +143,19 @@ BOOST_AUTO_TEST_CASE(derivedIncrementDouble) {
   }
 }
 
+BOOST_AUTO_TEST_CASE(testBoostVisitor) {
+  {
+    boost::variant<int, std::string, double, uint64_t> a = 10;
+    boost::variant<int, std::string, double, uint64_t> b = 11;
+    auto value = boost::apply_visitor(VariantVisitorAdd(), a, b);
+  }
+  {
+    boost::variant<int, std::string, double, uint64_t> a = 10;
+    boost::variant<int, std::string, double, uint64_t> b = 10.10;
+    BOOST_CHECK_THROW(boost::apply_visitor(VariantVisitorAdd(), a, b), o2::monitoring::MonitoringInternalException);
+  }
+}
+
 } // namespace Test
 } // namespace monitoring
 } // namespace o2