feat(ecs): implement symmetric relation querying

core/include/cubos/core/ecs/query/filter.hpp

@@ -71,6 +71,9 @@ namespace cubos::core::ecs
             /// @brief Relation data type.
             DataTypeId dataType;
 
+            /// @brief Whether the link is symmetric.
+            bool isSymmetric;
+
             /// @brief From target index.
             int fromTarget;
 
@@ -80,8 +83,23 @@ namespace cubos::core::ecs
             /// @brief Tables which match the link, found through calls to @ref update().
             std::vector<SparseRelationTableId> tables;
 
+            /// @brief Tables which match the reverse link, found through calls to @ref update().
+            ///
+            /// Only filled if @ref isSymmetric is true.
+            std::vector<SparseRelationTableId> reverseTables;
+
+            /// @brief Whether each of the tables in @ref reverseTables is already in @ref tables.
+            ///
+            /// Only filled if @ref isSymmetric is true.
+            std::vector<bool> reverseTablesSeen;
+
             /// @brief How many tables have already been seen through @ref SparseRelationTableRegistry::collect.
             std::size_t seenCount{0};
+
+            /// @brief Gets the nth table in the link, as if the reverseTables vector was appended to the end of the
+            /// tables vector.
+            /// @param index Table index.
+            SparseRelationTableId table(std::size_t index) const;
         };
 
         World& mWorld;

core/include/cubos/core/ecs/table/sparse_relation/registry.hpp

@@ -93,19 +93,15 @@ namespace cubos::core::ecs
         /// @param index Entity index.
         void erase(ArchetypeId archetype, uint32_t index);
 
-        /// @brief Collects new tables which match the given filter.
-        /// @param[out] tables Vector to insert the table identifiers into.
+        /// @brief Calls the given function for each new table.
         /// @param counter Counter previously returned by this function. Zero should be used for the first call.
-        /// @param filter Function which receives a table identifier and returns a boolean.
+        /// @param func Function which receives a table identifier.
         /// @return Counter to be passed to this function in a future call.
-        std::size_t collect(std::vector<SparseRelationTableId>& tables, std::size_t counter, auto filter)
+        std::size_t forEach(std::size_t counter, auto func)
         {
             for (; counter < mIds.size(); ++counter)
             {
-                if (filter(mIds[counter]))
-                {
-                    tables.emplace_back(mIds[counter]);
-                }
+                func(mIds[counter]);
             }
 
             return counter;