Simplify implementation and add a new access operators[](ItemId)

The new operator behaves exactly as the
SubItemValuePerItem::itemArray(ItemId) and
SubItemArrayPerItem::itemTable(ItemId) functions

This convenient change is mainly made in the goal of simplifying
item-to-item matrices used in connectivity

src/mesh/SubItemArrayPerItem.hpp

@@ -90,8 +90,14 @@ class SubItemArrayPerItem
     return m_values[m_host_row_map(size_t{item_id}) + i];
   }
 
-  // Following Kokkos logic, these classes are view and const view does allow
-  // changes in data
+  template <ItemType item_t>
+  Table<DataType>
+  operator[](const ItemIdT<item_t>& item_id) const noexcept(NO_ASSERT)
+  {
+    static_assert(item_t == item_type, "invalid ItemId type");
+    return this->itemTable(item_id);
+  }
+
   template <typename ArrayIndexType>
   Array<DataType>
   operator[](const ArrayIndexType& i) const noexcept(NO_ASSERT)
@@ -144,20 +150,6 @@ class SubItemArrayPerItem
     m_values.fill(data);
   }
 
-  template <typename IndexType>
-  PUGS_INLINE Table<DataType>
-  itemTable(IndexType item_id) noexcept(NO_ASSERT)
-  {
-    static_assert(std::is_same_v<IndexType, ItemId>, "index must be an ItemId");
-    Assert(this->isBuilt());
-    Assert(item_id < this->numberOfItems());
-    const auto& item_begin = m_host_row_map(size_t{item_id});
-    const auto& item_end   = m_host_row_map(size_t{item_id} + 1);
-    return subTable(m_values, item_begin, item_end - item_begin, 0, this->sizeOfArrays());
-  }
-
-  // Following Kokkos logic, these classes are view and const view does allow
-  // changes in data
   template <typename IndexType>
   PUGS_INLINE Table<DataType>
   itemTable(IndexType item_id) const noexcept(NO_ASSERT)

src/mesh/SubItemValuePerItem.hpp

@@ -88,8 +88,14 @@ class SubItemValuePerItem
     return m_values[m_host_row_map(size_t{item_id}) + i];
   }
 
-  // Following Kokkos logic, these classes are view and const view does allow
-  // changes in data
+  template <ItemType item_t>
+  Array<DataType>
+  operator[](const ItemIdT<item_t>& item_id) const noexcept(NO_ASSERT)
+  {
+    static_assert(item_t == item_type, "invalid ItemId type");
+    return this->itemArray(item_id);
+  }
+
   template <typename ArrayIndexType>
   DataType&
   operator[](const ArrayIndexType& i) const noexcept(NO_ASSERT)
@@ -137,21 +143,7 @@ class SubItemValuePerItem
 
   template <typename IndexType>
   PUGS_INLINE Array<DataType>
-  itemArray(IndexType item_id) noexcept(NO_ASSERT)
-  {
-    static_assert(std::is_same_v<IndexType, ItemId>, "index must be an ItemId");
-    Assert(this->isBuilt());
-    Assert(item_id < this->numberOfItems());
-    const auto& item_begin = m_host_row_map(size_t{item_id});
-    const auto& item_end   = m_host_row_map(size_t{item_id} + 1);
-    return subArray(m_values, item_begin, item_end - item_begin);
-  }
-
-  // Following Kokkos logic, these classes are view and const view does allow
-  // changes in data
-  template <typename IndexType>
-  PUGS_INLINE Array<DataType>
-  itemArray(IndexType item_id) const noexcept(NO_ASSERT)
+  itemArray(const IndexType& item_id) const noexcept(NO_ASSERT)
   {
     static_assert(std::is_same_v<IndexType, ItemId>, "index must be an ItemId");
     Assert(this->isBuilt());