page size macro/utility

TODO

@@ -21,8 +21,7 @@
 * types defined at runtime that refer to the same compile-time type (but to different pools) are possible, the library is almost there
 * add take functionality, eg registry.take(entity, other); where it takes the entity and all its components from registry and move them to other
 * add entity function to views/groups (component -> owner, see sparse sets)
-
-* what about paged pools? vector of fixed-size blocks (ease shared components, multi-ownership, etc).
-  - still separate the three arrays, work with page size, not number of components, arrays don't have to have the same number of pages
-  - opaque input iterator that returns a proxy object (tuple of entity+references) and each can hide the underlying details about paging
-  - it can avoid [] most of the times, that annoying thing current it does and I dislike so much :-)
+* add opaque input iterators to views and groups that return tuples <entity, T &...> (proxy), multi-pass guaranteed
+* add fast lane for raw iterations, extend mt doc to describe allowed add/remove with pre-allocations on fast lanes
+* review sparse set to allow extrem customization (mix pack in the spec, base is position only)
+* paged reverse to reduce memory usage

src/entt/config/config.h

@@ -39,4 +39,9 @@ using maybe_atomic_t = Type;
 #endif // ENTT_ENTITY_TYPE
 
 
+#ifndef ENTT_PAGE_SIZE
+#define ENTT_PAGE_SIZE 32768
+#endif
+
+
 #endif // ENTT_CONFIG_CONFIG_H

src/entt/core/type_traits.hpp

@@ -65,6 +65,19 @@ template<class Type>
 constexpr auto is_named_type_v = is_named_type<Type>::value;
 
 
+/**
+ * @brief Helper variable template.
+ *
+ * `ENTT_PAGE_SIZE` if it's a power of two, a compilation error otherwise.
+ */
+constexpr auto page_size_v = []() constexpr {
+    constexpr auto size = ENTT_PAGE_SIZE;
+    // compile-time assertion if page size isn't a power of two
+    static_assert(size && ((size & (size - 1)) == 0));
+    return size;
+}();
+
+
 }
 
 
@@ -86,7 +99,9 @@ constexpr auto is_named_type_v = is_named_type<Type>::value;
     template<>\
     struct entt::named_type_traits<type>\
         : std::integral_constant<typename entt::hashed_string::hash_type, entt::hashed_string::to_value(#type)>\
-    {};
+    {\
+        static_assert(std::is_same_v<std::decay_t<type>, type>);\
+    };
 
 
 /**