Implement filter method

tests/zecsy.cpp

@@ -207,6 +207,7 @@ TEST_CASE("Create a simple system that processes entities with a specific "
      */
     w.query<Component>([](entity_id e, Component& c) { c.value++; });
 
+    REQUIRE(w.filter<Component>().size() == 2);
     REQUIRE(w.get<Component>(e0).value == 1);
     REQUIRE(w.get<Component>(e1).value == 21);
 }
@@ -247,6 +248,9 @@ TEST_CASE("Test a systems ability to query and process only entities with a "
             c1.value++;
         });
 
+    REQUIRE(w.filter<C0, C1>().size() == 1);
+    REQUIRE(w.filter<C0, C1>()[0] == e0);
+
     REQUIRE(w.get<C0>(e0).value == 1);
     REQUIRE(w.get<C1>(e0).value == 11);
 

zecsy.hpp

@@ -78,6 +78,9 @@ namespace zecsy
         template<Component First, Component Second, Component... Rest>
         void remove(entity_id e);
 
+        template<Component... T>
+        std::vector<entity_id> filter();
+
         template<Component... T>
         void query(std::invocable<entity_id, T&...> auto&& system);
 
@@ -86,9 +89,10 @@ namespace zecsy
 
     private:
         using comp_id = size_t;
-        using zecsy_bits = std::bitset<ZECSY_MAX_COMPONENTS>;
+        using entity_group = std::set<entity_id>;
+        using archetype_signature = std::bitset<ZECSY_MAX_COMPONENTS>;
 
-        std::unordered_map<entity_id, zecsy_bits> entity_to_comps;
+        std::unordered_map<entity_id, archetype_signature> entity_to_comps;
         entity_id entity_counter = 0;
 
         size_t query_archetypes_checked = 0;
@@ -102,10 +106,6 @@ namespace zecsy
         };
 
         std::unordered_map<comp_id, component_pool> pools;
-
-        using archetype_signature = zecsy_bits;
-        using entity_group = std::set<entity_id>;
-
         std::unordered_map<archetype_signature, entity_group> archetypes;
 
         template<Component T>
@@ -349,10 +349,8 @@ namespace zecsy
     }
 
     template<Component... T>
-    inline void world::query(std::invocable<entity_id, T&...> auto&& system)
+    inline std::vector<entity_id> world::filter()
     {
-        /*std::vector<comp_id> required = {get_component_id<T>()...};*/
-
         archetype_signature required;
 
         (required.set(get_component_id<T>()), ...);
@@ -360,6 +358,8 @@ namespace zecsy
         query_archetypes_checked = 0;
         query_entities_processed = 0;
 
+        std::vector<entity_id> result;
+
         for(const auto& [archetype_key, entities]: archetypes)
         {
             query_archetypes_checked++;
@@ -367,11 +367,19 @@ namespace zecsy
             if((archetype_key & required) == required)
             {
                 query_entities_processed += entities.size();
-                for(entity_id e: entities)
-                {
-                    system(e, get<T>(e)...);
-                }
+                result.insert(result.end(), entities.begin(), entities.end());
             }
         }
+
+        return result;
+    }
+
+    template<Component... T>
+    inline void world::query(std::invocable<entity_id, T&...> auto&& system)
+    {
+        for(auto e: filter<T...>())
+        {
+            system(e, get<T>(e)...);
+        }
     }
 }; // namespace zecsy