Generalize the DenseVectorSpan for ranges

dune/common/densevectorspan.hh

@@ -14,9 +14,23 @@
 #include <dune/common/densevector.hh>
 #include <dune/common/ftraits.hh>
 #include <dune/common/typetraits.hh>
+#include <dune/common/std/default_accessor.hh>
+#include <dune/common/std/iterator_accessor.hh>
+#include <dune/common/std/layout_right.hh>
 #include <dune/common/std/mdspan.hh>
 
 namespace Dune {
+namespace Impl {
+
+template <class V>
+concept IsVector = requires(V v)
+{
+  v.data();
+  { v.size() } -> std::integral;
+};
+
+} // end namespace Impl
+
 
 /** @addtogroup DenseMatVec
   *  @{
@@ -27,13 +41,13 @@ namespace Dune {
   * \tparam K is the field type (use float, double, complex, etc)
   * \tparam Extent The static size of the vector or `Std::dynamic_extent` if the size is dynamic
   */
-template <class K, std::size_t Extent = Std::dynamic_extent>
+template <class K, std::size_t Extent = Std::dynamic_extent, class Accessor = Std::default_accessor<K>>
 class DenseVectorSpan
-    : private Std::mdspan< K, Std::extents<std::size_t,Extent> >
-    , public DenseVector< DenseVectorSpan<K, Extent> >
+    : private Std::mdspan< K, Std::extents<std::size_t,Extent>, Std::layout_right, Accessor >
+    , public DenseVector< DenseVectorSpan<K, Extent, Accessor> >
 {
-  using Base = Std::mdspan< K, Std::extents<std::size_t,Extent> >;
-  using Interface = DenseVector< DenseVectorSpan<K, Extent> >;
+  using Base = Std::mdspan< K, Std::extents<std::size_t,Extent>, Std::layout_right, Accessor >;
+  using Interface = DenseVector< DenseVectorSpan<K, Extent, Accessor> >;
 
 public:
   // import all constructors from Std::mdspan
@@ -54,6 +68,16 @@ public:
     : Base(v.data(), v.size())
   {}
 
+  //! Construct a span over an iterator range
+  template <class Range>
+    requires (not Impl::IsVector<Range>) && requires(Range&& r) {
+      { r.begin() } -> std::convertible_to<typename Base::data_handle_type>;
+      { r.end()   } -> std::convertible_to<typename Base::data_handle_type>;
+    }
+  constexpr DenseVectorSpan (Range&& r) noexcept
+    : Base(r.begin(), std::distance(r.begin(), r.end()))
+  {}
+
   // make assignment of other vectors possible
   using Interface::operator=;
 
@@ -134,17 +158,35 @@ template <class K, int N>
 DenseVectorSpan (FieldVector<K,N> const&)
   -> DenseVectorSpan<const K,std::size_t(N)>;
 
+// span over an iterator range
+
+template <class Range, class Iter = decltype(std::declval<Range>().begin())>
+  requires (not Impl::IsVector<Range>) && requires(Range& r) {
+    { r.begin() } -> std::convertible_to<Iter>;
+    { r.end() } -> std::convertible_to<Iter>;
+  }
+DenseVectorSpan (Range&)
+  -> DenseVectorSpan<typename std::iterator_traits<Iter>::value_type, Std::dynamic_extent, Std::iterator_accessor<Iter>>;
+
+template <class Range, class Iter = decltype(std::declval<Range>().cbegin())>
+  requires (not Impl::IsVector<Range>) && requires(const Range& r) {
+    { r.begin() } -> std::convertible_to<Iter>;
+    { r.end() } -> std::convertible_to<Iter>;
+  }
+DenseVectorSpan (const Range&)
+  -> DenseVectorSpan<typename std::iterator_traits<Iter>::value_type, Std::dynamic_extent, Std::iterator_accessor<Iter>>;
+
 
-template <class K, std::size_t Extent>
-struct DenseMatVecTraits< DenseVectorSpan<K, Extent> >
+template <class K, std::size_t Extent, class Accessor>
+struct DenseMatVecTraits< DenseVectorSpan<K, Extent, Accessor> >
 {
-  using derived_type = DenseVectorSpan<K, Extent>;
+  using derived_type = DenseVectorSpan<K, Extent, Accessor>;
   using value_type = K;
   using size_type = std::size_t;
 };
 
-template <class K, std::size_t Extent>
-struct FieldTraits< DenseVectorSpan<K, Extent> >
+template <class K, std::size_t Extent, class Accessor>
+struct FieldTraits< DenseVectorSpan<K, Extent, Accessor> >
 {
   using field_type = typename FieldTraits<K>::field_type;
   using real_type = typename FieldTraits<K>::real_type;

dune/common/std/CMakeLists.txt

@@ -5,6 +5,7 @@ install(FILES
   default_accessor.hh
   extents.hh
   functional.hh
+  iterator_accessor.hh
   layout_left.hh
   layout_right.hh
   layout_stride.hh

dune/common/std/iterator_accessor.hh

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
+// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
+#ifndef DUNE_COMMON_STD_ITERATOR_ACCESSOR_HH
+#define DUNE_COMMON_STD_ITERATOR_ACCESSOR_HH
+
+#include <iterator>
+
+namespace Dune::Std {
+
+/**
+ * \brief A type for access to elements of mdspan using iterators as data handle.
+ * \ingroup CxxUtilities
+ *
+ * The `iterator_accessor` class template is an `AccessorPolicy` used by `mdspan`
+ * to provide access to elements in an iterator range [begin, end). The iterator
+ * thereby acts as a data handle.
+ *
+ * \tparam Iterator  The iterator type should be conforming with the std iterator concept.
+ */
+template <class Iterator>
+class iterator_accessor
+{
+public:
+  using element_type = typename std::iterator_traits<Iterator>::value_type;
+  using data_handle_type = Iterator;
+  using reference = typename std::iterator_traits<Iterator>::reference;
+  using offset_policy = iterator_accessor;
+
+public:
+  /// \brief Default constructor
+  constexpr iterator_accessor () noexcept = default;
+
+  /// \brief Return a reference to the i'th element in the data range starting at `p`
+  constexpr reference access (data_handle_type p, std::size_t i) const noexcept
+  {
+    return *std::next(p,i);
+  }
+
+  /// \brief Return a data handle to the i'th element in the data range starting at `p`
+  constexpr data_handle_type offset (data_handle_type p, std::size_t i) const noexcept
+  {
+    return std::next(p,i);
+  }
+};
+
+} // end namespace Dune::Std
+
+#endif // DUNE_COMMON_STD_ITERATOR_ACCESSOR_HH

dune/common/test/densevectorspantest.cc

@@ -8,6 +8,7 @@
 
 #include <dune/common/dynmatrix.hh>
 #include <dune/common/densevectorspan.hh>
+#include <dune/common/iteratorrange.hh>
 #include <dune/common/test/testsuite.hh>
 
 int main()
@@ -45,5 +46,10 @@ int main()
     [[maybe_unused]] auto x_span2 = Dune::DenseVectorSpan(data);
   }
 
+  {
+    auto range = Dune::IteratorRange{x.begin(), x.end()};
+    [[maybe_unused]] auto x_span1 = Dune::DenseVectorSpan(range);
+  }
+
   return test.exit();
 }