SingleValueModelCheckerHelper: Fixed signature of getOptimizationDirection so that a const& is returned.

src/storm/modelchecker/helper/SingleValueModelCheckerHelper.cpp

@@ -21,7 +21,7 @@ namespace storm {
             }
             
             template <typename ValueType, storm::dd::DdType DdType>
-            storm::solver::OptimizationDirection SingleValueModelCheckerHelper<ValueType, DdType>::getOptimizationDirection() const {
+            storm::solver::OptimizationDirection const& SingleValueModelCheckerHelper<ValueType, DdType>::getOptimizationDirection() const {
                 STORM_LOG_ASSERT(isOptimizationDirectionSet(), "Requested optimization direction but none was set.");
                 return _optimizationDirection.get();
             }

src/storm/modelchecker/helper/SingleValueModelCheckerHelper.h

@@ -41,7 +41,7 @@ namespace storm {
                  * @pre an optimization direction has to be set before calling this.
                  * @return the optimization direction.
                  */
-                storm::solver::OptimizationDirection getOptimizationDirection() const;
+                storm::solver::OptimizationDirection const& getOptimizationDirection() const;
                 
                 /*!
                  * @pre an optimization direction has to be set before calling this.