Tile: tile-null-assert

src/TiledArray/tile.h

@@ -33,11 +33,14 @@ namespace TiledArray {
  * @{
  */
 
-/// An N-dimensional shallow-copy wrapper for Tensor-like types that, unlike
-/// Tensor, have deep-copy semantics. Like Tensor, Tile is
-/// default-constructible. The default constructor produced a Tile in
-/// null state (not referring to any tensor object). The name refers to its
-/// intended use as a tile of DistArray.
+/// A shallow-copy wrapper for deep-copy Tensor-like types. The name
+/// refers to its intended use as a tile of DistArray.
+/// Like Tensor, Tile is default-constructible. The default constructor
+/// produces a Tile in null state (not referring to any tensor object);
+/// calling reset() on a Tile also produces a null Tile.
+/// Most operations on a null Tile will produce a failing TA_ASSERT
+/// (see Tile::tensor()), even in cases where valid semantics could be defined
+/// (such as add_to).
 ///
 /// \tparam T a tensor type. It may provide a subset of the full operation
 /// set of Tensor, since only those operations that are actually used
@@ -196,9 +199,19 @@ class Tile {
 
   // Tile accessor -----------------------------------------------------------
 
-  tensor_type& tensor() { return *pimpl_; }
+  /// \return reference to the referred-to value
+  /// \pre TA_ASSERT that this is not in a null state
+  tensor_type& tensor() {
+    TA_ASSERT(pimpl_);
+    return *pimpl_;
+  }
 
-  const tensor_type& tensor() const { return *pimpl_; }
+  /// \return const reference to the referred-to value
+  /// \pre TA_ASSERT that this is not in a null state
+  const tensor_type& tensor() const {
+    TA_ASSERT(pimpl_);
+    return *pimpl_;
+  }
 
   // Iterator accessor -------------------------------------------------------
 

tests/CMakeLists.txt

@@ -41,6 +41,7 @@ set(ta_test_src_files  ta_test.cpp
     btas_zb_inner_tile.cpp
     tensor_tensor_view.cpp
     tensor_shift_wrapper.cpp
+    tile.cpp
     tiled_range1.cpp
     tiled_range.cpp
     blocked_pmap.cpp

tests/tile.cpp

@@ -0,0 +1,49 @@
+/*
+ *  This file is a part of TiledArray.
+ *  Copyright (C) 2026  Virginia Tech
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *  tile.cpp
+ *  September 24, 2026
+ *
+ */
+
+#include <TiledArray/config.h>
+
+#ifdef TILEDARRAY_HAS_BTAS
+
+#include <TiledArray/external/btas.h>
+#include <TiledArray/tile.h>
+#include "tiledarray.h"
+#include "unit_test_config.h"
+
+BOOST_AUTO_TEST_SUITE(tile_suite, TA_UT_LABEL_SERIAL)
+
+// TA::Tile is meant to wrap deep-copy tensor types, such as btas::Tensor
+using tile_type = TiledArray::Tile<btas::Tensor<double, TiledArray::Range>>;
+
+BOOST_AUTO_TEST_CASE(null_tile) {
+  tile_type null_tile;
+  const tile_type& const_null_tile = null_tile;
+  BOOST_CHECK(null_tile.empty());
+  BOOST_CHECK_EQUAL(null_tile.use_count(), 0);
+  // tensor() on a null tile must trigger TA_ASSERT
+  BOOST_CHECK_TA_ASSERT(null_tile.tensor(), TiledArray::Exception);
+  BOOST_CHECK_TA_ASSERT(const_null_tile.tensor(), TiledArray::Exception);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+#endif  // TILEDARRAY_HAS_BTAS