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+#ifndef ENTITY_MANAGER_CPP_42D78C22
+#define ENTITY_MANAGER_CPP_42D78C22
+
+#include "entity_manager.h"
+
+template <>
+std::set<EntityManager::id_type> EntityManager::getEntitiesWithComponents<>(
+  std::set<std::type_index>& componentTypes)
+{
+  if (cachedComponents.count(componentTypes) == 1)
+  {
+    return cachedComponents[componentTypes];
+  }
+
+  std::set<id_type>& cache = cachedComponents[componentTypes];
+  for (id_type entity = 0; entity < entities.size(); entity++)
+  {
+    EntityData& data = entities[entity];
+    bool cacheEntity = true;
+
+    for (auto& componentType : componentTypes)
+    {
+      if (data.components.count(componentType) == 0)
+      {
+        cacheEntity = false;
+        break;
+      }
+    }
+
+    if (cacheEntity)
+    {
+      cache.insert(entity);
+    }
+  }
+
+  return cache;
+}
+
+#endif /* end of include guard: ENTITY_MANAGER_CPP_42D78C22 */