[networkbuilder] increase robustness of non-embedded entity adder

frackit/entitynetwork/networkbuilder.hh

@@ -541,8 +541,12 @@ public:
     /*!
      * \brief Adds an entity to the network.
      *        This function can be used when no sub-domain
-     *        specifications are made. Internally, the entity
-     *        is added to the sub-domain with index 0.
+     *        specifications are made.
+     * \note Internally, the entity is added to a dummy
+     *       sub-domain with id std::numeric_limits<std::size_t>::max().
+     *       Thus, this could lead to clashes if users define sub-domains
+     *       with this id. The entities will then be merged into one embedded
+     *       network.
      * \return The id of the newly added entity
      */
     template<class Entity>
@@ -555,7 +559,8 @@ public:
             throw std::runtime_error("Entity dimension must be smaller than domain dimension");
 
         this->entityDimension_ = entityDim;
-        return Id{this->bindEntity_(0, OCCUtilities::getShape(entity))};
+        const auto subDomainId = std::numeric_limits<std::size_t>::max();
+        return Id{this->bindEntity_(subDomainId, OCCUtilities::getShape(entity))};
     }
 
     /*!