Adds SmoothView (#185)

* almost works [skip ci]

* back up [skip ci]

* r2g

* Committing clang-format changes

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

include/tensorwrapper/detail_/polymorphic_base.hpp

@@ -103,8 +103,13 @@ class PolymorphicBase {
      *  @throw None No throw guarantee.
      */
     bool are_equal(const_base_reference rhs) const noexcept {
+        // Downcast *this so it can be passed to are_equal_
         const_base_reference plhs = static_cast<const_base_reference>(*this);
-        return are_equal_(rhs) && rhs.are_equal_(plhs);
+
+        // This line is necessary if are_equal_ is overriden in BaseType
+        const PolymorphicBase& rhs_upcast = rhs;
+
+        return are_equal_(rhs) && rhs_upcast.are_equal_(plhs);
     }
 
     /** @brief Determines if *this and @p rhs are polymorphically different.

include/tensorwrapper/detail_/view_traits.hpp

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2024 NWChemEx-Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <type_traits>
+
+namespace tensorwrapper::detail_ {
+
+/** @brief Is the cast from @p FromType to @p ToType just adding const?
+ *
+ *  A common TMP pattern in implementing views is needing to convert mutable
+ *  views to read-only views. This trait can be used to compare the template
+ *  type parameters of two views (assuming the views are templated on what
+ *  object they are acting like) in order to determine if they represent a
+ *  conversion from @p FromType to @p ToType such that @p ToType is
+ *  `const FromType`. If @p ToType is `const FromType` this template variable
+ *  will be set to true, otherwise it will be set to false.
+ *
+ *  @tparam FromType The type we are converting from.
+ *  @tparam ToType The type we are converting to.
+ */
+template<typename FromType, typename ToType>
+constexpr bool is_mutable_to_immutable_cast_v =
+  !std::is_const_v<FromType> &&           // FromType is NOT read-only
+  std::is_const_v<ToType> &&              // ToType is read-only
+  std::is_same_v<const FromType, ToType>; // They differ by const-ness
+
+/** @brief Disables a templated function except when
+ *         `is_mutable_to_immutable_cast_v<FromType, ToType>` evaluates to true.
+ *
+ *  If `View` is a template class with template parameter type `T`, we want the
+ *  implicit conversion from `View<T>` to `View<const T>` to exist. In practice,
+ *  this leaves us with two options: partial specialization of `View` for
+ *  const-qualified types or use of SFINAE to disable the conversion. We prefer
+ *  the latter as the former requires us to duplicate the entirety of the
+ *  class. This template type will disable the accompanying function via SFINAE
+ *  if @p ToType is not `const FromType`.
+ *
+ *  @tparam FromType The type we are converting from. Expected to be the
+ *                   template type parameter of the view we are casting from.
+ *  @tparam ToType The type we are converting to. Expected to be the template
+ *                 type parameter of the view we are casting to.
+ */
+template<typename FromType, typename ToType>
+using enable_if_mutable_to_immutable_cast_t =
+  std::enable_if_t<is_mutable_to_immutable_cast_v<FromType, ToType>>;
+
+} // namespace tensorwrapper::detail_

include/tensorwrapper/shape/shape_base.hpp

@@ -18,6 +18,9 @@
 #include <cstddef>
 #include <memory>
 #include <tensorwrapper/detail_/polymorphic_base.hpp>
+#include <tensorwrapper/shape/shape_traits.hpp>
+#include <tensorwrapper/shape/smooth_view.hpp>
+
 namespace tensorwrapper::shape {
 
 /** @brief Code factorization for the various types of shapes.
@@ -34,19 +37,29 @@ namespace tensorwrapper::shape {
  *  - get_rank_()
  *  - get_size_()
  */
-class ShapeBase : public detail_::PolymorphicBase<ShapeBase> {
+class ShapeBase : public tensorwrapper::detail_::PolymorphicBase<ShapeBase> {
+private:
+    /// Type implementing the traits of this
+    using traits_type = ShapeTraits<ShapeBase>;
+
 public:
     /// Type all shapes inherit from
-    using shape_base = ShapeBase;
+    using shape_base = typename traits_type::shape_base;
 
     /// Type of a pointer to the base of a shape object
-    using base_pointer = std::unique_ptr<shape_base>;
+    using base_pointer = typename traits_type::base_pointer;
 
     /// Type used to hold the rank of a tensor
-    using rank_type = unsigned short;
+    using rank_type = typename traits_type::rank_type;
 
     /// Type used to specify the number of elements in the shape
-    using size_type = std::size_t;
+    using size_type = typename traits_type::size_type;
+
+    /// Type of an object acting like a mutable reference to a Smooth shape
+    using smooth_reference = SmoothView<Smooth>;
+
+    /// Type of an object acting like a read-only reference to a Smooth shape
+    using const_smooth_reference = SmoothView<const Smooth>;
 
     /// No-op for ShapeBase because ShapeBase has no state
     ShapeBase() noexcept = default;
@@ -83,6 +96,34 @@ class ShapeBase : public detail_::PolymorphicBase<ShapeBase> {
      */
     size_type size() const noexcept { return get_size_(); }
 
+    /** @brief Returns a view of *this as a Smooth object.
+     *
+     *  It is possible to view any shape as a smooth shape. For more exotic
+     *  shapes this may require flattening nestings and padding dimensions.
+     *  This method ultimately dispatches to the as_smooth_ overload of the
+     *  derived class to control how to smooth the shape out.
+     *
+     *  @return A view of *this consistent with thinking of *this as a Smooth
+     *          object.
+     *
+     *  @throw std::bad_alloc if there is a problem allocating the view. Strong
+     *                        throw guarantee.
+     */
+    smooth_reference as_smooth() { return as_smooth_(); }
+
+    /** @brief Returns a read-only view of *this as a Smooth object.
+     *
+     *  This method works the same as the non-const version except that the
+     *  resulting view is read-only.
+     *
+     *  @return A read-only view of *this consistent with thinking of *this as
+     *          a Smooth object.
+     *
+     *  @throw std::bad_alloc if there is a problem allocating the view. Strong
+     *                        throw guarantee.
+     */
+    const_smooth_reference as_smooth() const { return as_smooth_(); }
+
 protected:
     /** @brief Used to implement rank().
      *
@@ -108,6 +149,12 @@ class ShapeBase : public detail_::PolymorphicBase<ShapeBase> {
      *              subject to a no-throw guarantee.
      */
     virtual size_type get_size_() const noexcept = 0;
+
+    /// Derived class should override to be consistent with as_smooth()
+    virtual smooth_reference as_smooth_() = 0;
+
+    /// Derived class should override to be consistent with as_smooth() const
+    virtual const_smooth_reference as_smooth_() const = 0;
 };
 
 } // namespace tensorwrapper::shape

include/tensorwrapper/shape/shape_fwd.hpp

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2024 NWChemEx-Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+namespace tensorwrapper::shape {
+namespace detail_ {
+
+template<typename SmoothType>
+class SmoothViewPIMPL;
+
+}
+
+class ShapeBase;
+
+class Smooth;
+
+template<typename SmoothType>
+class SmoothView;
+
+} // namespace tensorwrapper::shape

include/tensorwrapper/shape/shape_traits.hpp

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2024 NWChemEx-Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <memory>
+#include <tensorwrapper/shape/shape_fwd.hpp>
+
+namespace tensorwrapper::shape {
+
+template<typename ShapeType>
+struct ShapeTraits;
+
+template<>
+struct ShapeTraits<ShapeBase> {
+    using shape_base   = ShapeBase;
+    using base_pointer = std::unique_ptr<shape_base>;
+    using rank_type    = unsigned short;
+    using size_type    = std::size_t;
+};
+
+template<>
+struct ShapeTraits<const ShapeBase> {
+    using shape_base   = ShapeBase;
+    using base_pointer = std::unique_ptr<shape_base>;
+    using rank_type    = unsigned short;
+    using size_type    = std::size_t;
+};
+
+template<>
+struct ShapeTraits<Smooth> : public ShapeTraits<ShapeBase> {
+    using value_type       = Smooth;
+    using const_value_type = const value_type;
+    using reference        = value_type&;
+    using const_reference  = const value_type&;
+    using pointer          = value_type*;
+    using const_pointer    = const value_type*;
+};
+
+template<>
+struct ShapeTraits<const Smooth> : public ShapeTraits<const ShapeBase> {
+    using value_type       = Smooth;
+    using const_value_type = const value_type;
+    using reference        = const value_type&;
+    using const_reference  = const value_type&;
+    using pointer          = const value_type*;
+    using const_pointer    = const value_type*;
+};
+
+template<typename T>
+struct ShapeTraits<SmoothView<T>> {
+    using smooth_traits = ShapeTraits<T>;
+    using pimpl_type    = detail_::SmoothViewPIMPL<T>;
+    using const_pimpl_type =
+      detail_::SmoothViewPIMPL<typename smooth_traits::const_value_type>;
+    using pimpl_pointer       = std::unique_ptr<pimpl_type>;
+    using const_pimpl_pointer = std::unique_ptr<const_pimpl_type>;
+};
+
+} // namespace tensorwrapper::shape

include/tensorwrapper/shape/smooth.hpp

@@ -166,6 +166,12 @@ class Smooth : public ShapeBase {
                                size_type(1), std::multiplies<size_type>());
     }
 
+    smooth_reference as_smooth_() override { return smooth_reference(*this); }
+
+    virtual const_smooth_reference as_smooth_() const override {
+        return const_smooth_reference(*this);
+    }
+
     /// Implements are_equal by calling ShapeBase::are_equal_impl_
     bool are_equal_(const ShapeBase& rhs) const noexcept override {
         return are_equal_impl_<Smooth>(rhs);