storage: removed storage category

src/entt/entity/group.hpp

@@ -600,11 +600,11 @@ class basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...> final
     public:
         using iterator = iterable_group_iterator<
             typename basic_sparse_set<Entity>::iterator,
-            type_list_cat_t<std::conditional_t<std::is_same_v<typename storage_type<Owned>::storage_category, empty_storage_tag>, type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().end())>>...>
+            type_list_cat_t<std::conditional_t<std::is_void_v<decltype(std::declval<storage_type<Owned>>().get({}))>, type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().end())>>...>
         >;
         using reverse_iterator = iterable_group_iterator<
             typename basic_sparse_set<Entity>::reverse_iterator,
-            type_list_cat_t<std::conditional_t<std::is_same_v<typename storage_type<Owned>::storage_category, empty_storage_tag>, type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().rbegin())>>...>
+            type_list_cat_t<std::conditional_t<std::is_void_v<decltype(std::declval<storage_type<Owned>>().get({}))>, type_list<>, type_list<decltype(std::declval<storage_type<Owned>>().rbegin())>>...>
         >;
 
         [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {

src/entt/entity/storage.hpp

@@ -199,8 +199,6 @@ public:
     using reverse_iterator = Type *;
     /*! @brief Constant reverse iterator type. */
     using const_reverse_iterator = const Type *;
-    /*! @brief Storage category. */
-    using storage_category = dense_storage_tag;
 
     /**
      * @brief Increases the capacity of a storage.
@@ -519,8 +517,6 @@ public:
     using entity_type = Entity;
     /*! @brief Unsigned integer type. */
     using size_type = std::size_t;
-    /*! @brief Storage category. */
-    using storage_category = empty_storage_tag;
 
     /**
      * @brief Fake get function.
@@ -594,8 +590,6 @@ struct storage_adapter_mixin: Type {
     using value_type = typename Type::value_type;
     /*! @brief Underlying entity identifier. */
     using entity_type = typename Type::entity_type;
-    /*! @brief Storage category. */
-    using storage_category = typename Type::storage_category;
 
     /**
      * @brief Assigns entities to a storage.
@@ -662,8 +656,6 @@ public:
     using value_type = typename Type::value_type;
     /*! @brief Underlying entity identifier. */
     using entity_type = typename Type::entity_type;
-    /*! @brief Storage category. */
-    using storage_category = typename Type::storage_category;
 
     /**
      * @brief Returns a sink object.
@@ -820,11 +812,10 @@ template<typename Type>
 [[nodiscard]] auto get_as_tuple([[maybe_unused]] Type &container, [[maybe_unused]] const typename Type::entity_type entity) {
     static_assert(std::is_same_v<std::remove_const_t<Type>, typename storage_traits<typename Type::entity_type, typename Type::value_type>::storage_type>);
 
-    if constexpr(std::is_base_of_v<dense_storage_tag, typename Type::storage_category>) {
-        return std::forward_as_tuple(container.get(entity));
-    } else {
-        static_assert(std::is_base_of_v<empty_storage_tag, typename Type::storage_category>, "Unknown storage category");
+    if constexpr(std::is_void_v<decltype(container.get({}))>) {
         return std::make_tuple();
+    } else {
+        return std::forward_as_tuple(container.get(entity));
     }
 }
 

src/entt/entity/view.hpp

@@ -245,7 +245,7 @@ class basic_view<Entity, exclude_t<Exclude...>, Component...> final {
 
     template<typename Comp, typename Func>
     void traverse(Func func) const {
-        if constexpr(std::is_same_v<typename storage_type<Comp>::storage_category, empty_storage_tag>) {
+        if constexpr(std::is_void_v<decltype(std::get<storage_type<Comp> *>(pools)->get({}))>) {
             for(const auto entt: static_cast<const basic_sparse_set<entity_type> &>(*std::get<storage_type<Comp> *>(pools))) {
                 if(((std::is_same_v<Comp, Component> || std::get<storage_type<Component> *>(pools)->contains(entt)) && ...)
                     && !(std::get<const storage_type<Exclude> *>(filter)->contains(entt) || ...))
@@ -625,12 +625,12 @@ class basic_view<Entity, exclude_t<>, Component> final {
 
     public:
         using iterator = std::conditional_t<
-            std::is_same_v<typename storage_type::storage_category, empty_storage_tag>,
+            std::is_void_v<decltype(std::declval<storage_type>().get({}))>,
             iterable_view_iterator<typename basic_sparse_set<Entity>::iterator>,
             iterable_view_iterator<typename basic_sparse_set<Entity>::iterator, decltype(std::declval<storage_type>().begin())>
         >;
         using reverse_iterator = std::conditional_t<
-            std::is_same_v<typename storage_type::storage_category, empty_storage_tag>,
+            std::is_void_v<decltype(std::declval<storage_type>().get({}))>,
             iterable_view_iterator<typename basic_sparse_set<Entity>::reverse_iterator>,
             iterable_view_iterator<typename basic_sparse_set<Entity>::reverse_iterator, decltype(std::declval<storage_type>().rbegin())>
         >;
@@ -880,7 +880,7 @@ public:
      */
     template<typename Func>
     void each(Func func) const {
-        if constexpr(std::is_same_v<typename storage_type::storage_category, empty_storage_tag>) {
+        if constexpr(std::is_void_v<decltype(pool->get({}))>) {
             if constexpr(std::is_invocable_v<Func>) {
                 for(auto pos = size(); pos; --pos) {
                     func();