Add shape::, array_ref::, and array::bounds()

Helps avoid the common mistake of creating an array from an existing
argument's shape, inheriting the strides and possibly violating
compile-time constraints. (e.g. creating a planar image from an
interleaved image's shape).

Author: fbleibel-g

include/array/array.h

@@ -1030,6 +1030,12 @@ NDARRAY_HOST_DEVICE const DimsSrc& assert_dims_compatible(const DimsSrc& src) {
   return src;
 }
 
+/** Return a tuple of generic `dims` with same min and extents and all strides set to `unresolved`. */
+template <class Dims, size_t... Is>
+auto bounds_tuple(const Dims& dims, index_sequence<Is...>) {
+    return std::make_tuple(dim<>(std::get<Is>(dims).min(), std::get<Is>(dims).extent(), unresolved)...);
+}
+
 } // namespace internal
 
 template <class... Dims>
@@ -1293,6 +1299,13 @@ class shape {
   NDARRAY_HOST_DEVICE index_t rows() const { return i().extent(); }
   NDARRAY_HOST_DEVICE index_t columns() const { return j().extent(); }
 
+  /** Returns a shape with dynamic dims, with the same min and extents but
+   * strides initialized to `nda::unresolved`. This can be used to create
+   * an array with the same dimensions but different compile-time constraints. */
+  NDARRAY_HOST_DEVICE auto bounds() const {
+    return make_shape_from_tuple(internal::bounds_tuple(dims_, dim_indices()));
+  }
+
   /** A shape is equal to another shape if the dim objects of each
    * dimension from both shapes are equal. */
   template <class... OtherDims, class = enable_if_same_rank<OtherDims...>>
@@ -2115,6 +2128,15 @@ class array_ref {
   }
   const nda::dim<> dim(size_t d) const { return shape_.dim(d); }
   NDARRAY_HOST_DEVICE size_type size() const { return shape_.size(); }
+  /** Returns a shape with dynamic dims, with the same min and extents but
+   * strides initialized to `nda::unresolved`. This can be used to create
+   * an array with the same dimensions but different compile-time constraints:
+   *
+   *   nda::array_ref<T, SrcShape> ref(...);
+   *   nda::array<T, DstShape> y(ref.bounds());  // Compact array with the same `min`
+   *                                             // and `extents` as `ref`.
+   */
+  NDARRAY_HOST_DEVICE auto bounds() const { return shape_.bounds(); }
   NDARRAY_HOST_DEVICE bool empty() const { return base() != nullptr ? shape_.empty() : true; }
   NDARRAY_HOST_DEVICE bool is_compact() const { return shape_.is_compact(); }
 
@@ -2577,6 +2599,15 @@ class array {
   }
   const nda::dim<> dim(size_t d) const { return shape_.dim(d); }
   size_type size() const { return shape_.size(); }
+  /** Returns a shape with dynamic dims, with the same min and extents but
+   * strides initialized to `nda::unresolved`. This can be used to create
+   * an array with the same dimensions but different compile-time constraints:
+   *
+   *   nda::array<T, SrcShape> other(...);
+   *   nda::array<T, DstShape> y(other.bounds());  // Compact array with the same `min`
+   *                                               // and `extents` as `other`.
+   */
+  auto bounds() const { return shape_.bounds(); }
   bool empty() const { return shape_.empty(); }
   bool is_compact() const { return shape_.is_compact(); }
 

test/array.cpp

@@ -59,6 +59,27 @@ TEST(array_default_constructor) {
   sparse.clear();
 }
 
+TEST(array_construct_from_bounds) {
+  // Illustrate creating an array from incompatible compile-time
+  // shapes using bounds().
+  using SrcShape = shape<dense_dim<>, dim<>>;
+  using DstShape = shape<dim<>, dense_dim<>>;  // dense_dim is swapped.
+
+  SrcShape src_shape({-1, 10}, {2, 5, /*stride =*/100});
+  auto src = array<int, SrcShape>(src_shape);
+  auto dst = array<int, DstShape>(src.bounds());
+
+  // min and extent are preserved.
+  ASSERT_EQ(src.dim<0>().min(), dst.dim<0>().min());
+  ASSERT_EQ(src.dim<0>().extent(), dst.dim<0>().extent());
+  ASSERT_EQ(src.dim<1>().min(), dst.dim<1>().min());
+  ASSERT_EQ(src.dim<1>().extent(), dst.dim<1>().extent());
+  // Ensure that `dst` did not inherit the strides of its parent and is
+  // created compact.
+  ASSERT(!src.is_compact());
+  ASSERT(dst.is_compact());
+}
+
 TEST(array_static_convertibility) {
   using A0 = array_of_rank<int, 0>;
   using A3 = array_of_rank<int, 3>;

test/shape.cpp

@@ -26,6 +26,7 @@ TEST(shape_scalar) {
   ASSERT_EQ(s.flat_extent(), 1);
   ASSERT_EQ(s.size(), 1);
   ASSERT_EQ(s(), 0);
+  ASSERT_EQ(s.bounds().rank(), 0);
 }
 
 TEST(shape_1d) {
@@ -205,6 +206,30 @@ TEST(auto_strides) {
   test_auto_strides<10>();
 }
 
+TEST(bounds) {
+  dim</* Min= */ 0, /* Extent= */ 10> x;
+  dense_dim<> y(-2, 12);
+  auto s = make_shape(x, y);
+  s.resolve();
+
+  auto bounds = s.bounds();
+  // Returns a generic shape w/o compile-time min, extents, or strides.
+  ASSERT_EQ(bounds.dim<0>().Min, dynamic);
+  ASSERT_EQ(bounds.dim<0>().Extent, dynamic);
+  ASSERT_EQ(bounds.dim<0>().Stride, dynamic);
+  ASSERT_EQ(bounds.dim<1>().Min, dynamic);
+  ASSERT_EQ(bounds.dim<1>().Extent, dynamic);
+  ASSERT_EQ(bounds.dim<1>().Stride, dynamic);
+  // Check that dynamic min and extents are preserved.
+  ASSERT_EQ(bounds.dim<0>().min(), x.min());
+  ASSERT_EQ(bounds.dim<0>().extent(), x.extent());
+  ASSERT_EQ(bounds.dim<1>().min(), y.min());
+  ASSERT_EQ(bounds.dim<1>().extent(), y.extent());
+  // Bounds have strides set to unresolved.
+  ASSERT_EQ(bounds.dim<0>().stride(), nda::unresolved);
+  ASSERT_EQ(bounds.dim<1>().stride(), nda::unresolved);
+}
+
 TEST(broadcast_dim) {
   dim<> x(0, 10, 1);
   broadcast_dim<> y;