Associate numbering to all ItemOfItemType possible instances

src/mesh/ItemOfItemType.hpp

@@ -30,4 +30,35 @@ using CellOfNode = ItemOfItemType<ItemType::cell, ItemType::node>;
 using FaceOfNode = ItemOfItemType<ItemType::face, ItemType::node>;
 using EdgeOfNode = ItemOfItemType<ItemType::edge, ItemType::node>;
 
+template <ItemType sub_item_type, ItemType item_type>
+constexpr inline int item_of_item_type_index;
+
+template <>
+constexpr inline int item_of_item_type_index<ItemType::face, ItemType::cell> = 0;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::edge, ItemType::cell> = 1;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::node, ItemType::cell> = 2;
+
+template <>
+constexpr inline int item_of_item_type_index<ItemType::cell, ItemType::face> = 3;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::edge, ItemType::face> = 4;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::node, ItemType::face> = 5;
+
+template <>
+constexpr inline int item_of_item_type_index<ItemType::cell, ItemType::edge> = 6;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::face, ItemType::edge> = 7;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::node, ItemType::edge> = 8;
+
+template <>
+constexpr inline int item_of_item_type_index<ItemType::cell, ItemType::node> = 9;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::face, ItemType::node> = 10;
+template <>
+constexpr inline int item_of_item_type_index<ItemType::edge, ItemType::node> = 11;
+
 #endif   // ITEM_OF_ITEM_TYPE_HPP