getRestriction added to DFT interface

Former-commit-id: ba114e4478

src/storage/dft/DFT.h

@@ -166,6 +166,11 @@ namespace storm {
                 return std::static_pointer_cast<DFTDependency<ValueType> const>(mElements[index]);
             }
             
+            std::shared_ptr<DFTRestriction<ValueType> const> getRestriction(size_t index) const {
+                assert(isRestriction(index));
+                return std::static_pointer_cast<DFTRestriction<ValueType> const>(mElements[index]);
+            }
+
             std::vector<std::shared_ptr<DFTBE<ValueType>>> getBasicElements() const {
                 std::vector<std::shared_ptr<DFTBE<ValueType>>> elements;
                 for (DFTElementPointer elem : mElements) {