/*==============================================================================

  Program:   Visualization Toolkit
  Module:    TestDataArrayRange.cxx

  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notice for more information.

==============================================================================*/

#include "vtkDataArrayRange.h"

#include "vtkAOSDataArrayTemplate.h"
#include "vtkDataArray.h"
#include "vtkFloatArray.h"
#include "vtkSOADataArrayTemplate.h"
#ifdef VTK_USE_SCALED_SOA_ARRAYS
#include "vtkScaledSOADataArrayTemplate.h"
#endif

#include <algorithm>
#include <numeric>
#include <type_traits>
#include <utility>

namespace
{

std::size_t NumErrors = 0;

#define TO_STRING(x) TO_STRING2(x)
#define TO_STRING2(x) #x
#define LOCATION() "line " TO_STRING(__LINE__) ""

#define CHECK_TYPEDEF(t1, t2)                                                                      \
  static_assert(std::is_same<typename std::decay<t1>::type, typename std::decay<t2>::type>{},      \
    "Type mismatch: '" #t1 "' not same as '" #t2 "' in " LOCATION())

#define CHECK_IS_BASE_TYPE_OF(t1, t2)                                                              \
  static_assert(std::is_base_of<typename std::decay<t1>::type, typename std::decay<t2>::type>{},   \
    "Type mismatch: '" #t1 "' not same as '" #t2 "' in " LOCATION())

// Various properties required by random access iterators:
#define CHECK_ITER_TYPE(type)                                                                      \
  do                                                                                               \
  {                                                                                                \
    static_assert(std::is_default_constructible<Iter>::value,                                      \
      "Iterator types must be default constructable at " LOCATION());                              \
    static_assert(std::is_copy_constructible<Iter>::value,                                         \
      "Iterator types must be copy constructible at " LOCATION());                                 \
    static_assert(std::is_copy_assignable<Iter>::value,                                            \
      "Iterator types must be copy assignable at " LOCATION());                                    \
    static_assert(                                                                                 \
      std::is_destructible<Iter>::value, "Iterator types must be destructible at " LOCATION());    \
  } while (false)

#define LOG_ERROR(message)                                                                         \
  do                                                                                               \
  {                                                                                                \
    ++NumErrors;                                                                                   \
    std::cerr << NumErrors << ": " << message << "\n";                                             \
  } while (false)

#define CHECK_TRUE(expr)                                                                           \
  do                                                                                               \
  {                                                                                                \
    if (!(expr))                                                                                   \
    {                                                                                              \
      LOG_ERROR("Expression not true: '" #expr << "' at " LOCATION());                             \
    }                                                                                              \
  } while (false)

#define CHECK_FALSE(expr)                                                                          \
  do                                                                                               \
  {                                                                                                \
    if ((expr))                                                                                    \
    {                                                                                              \
      LOG_ERROR("Expression expected to be false but is true: '" #expr << "' at " LOCATION());     \
    }                                                                                              \
  } while (false)

#define CHECK_EQUAL(v1, v2)                                                                        \
  do                                                                                               \
  {                                                                                                \
    if (!(v1 == v2))                                                                               \
    {                                                                                              \
      LOG_ERROR("Expressions not equal: '" #v1 "' (" << v1 << ") and '" #v2 "' (" << v2            \
                                                     << ") in " LOCATION());                       \
    }                                                                                              \
  } while (false)

#define CHECK_NOT_EQUAL(v1, v2)                                                                    \
  do                                                                                               \
  {                                                                                                \
    if (!(v1 != v2))                                                                               \
    {                                                                                              \
      LOG_ERROR("Expressions not equal: '" #v1 "' (" << v1 << ") and '" #v2 "' (" << v2            \
                                                     << ") in " LOCATION());                       \
    }                                                                                              \
  } while (false)

#define CHECK_EQUAL_NODUMP(v1, v2)                                                                 \
  do                                                                                               \
  {                                                                                                \
    if (!(v1 == v2))                                                                               \
    {                                                                                              \
      LOG_ERROR("Expressions not equal: '" #v1 "' and '" #v2 "' in " LOCATION());                  \
    }                                                                                              \
  } while (false)

#define CHECK_NOT_EQUAL_NODUMP(v1, v2)                                                             \
  do                                                                                               \
  {                                                                                                \
    if (!(v1 != v2))                                                                               \
    {                                                                                              \
      LOG_ERROR(                                                                                   \
        "Expressions should be unequal but aren't: '" #v1 "' and '" #v2 "' in " LOCATION());       \
    }                                                                                              \
  } while (false)

//==============================================================================
//==============================================================================
// Helpers:
//==============================================================================
//==============================================================================
template <typename Range>
void FillValueRangeIota(Range range)
{
  using ValueType = typename Range::ValueType;

  ValueType value{ 1 };
  std::iota(range.begin(), range.end(), value);
}

template <typename Range>
void TestIota(Range range)
{
  auto startValue = range.GetBeginValueId() + 1;
  auto endValue = range.GetEndValueId() + 1;

  auto value = startValue;

  for (auto comp : range)
  {
    CHECK_EQUAL(value, comp);
    ++value;
  }

  CHECK_EQUAL(value, endValue);
}

//==============================================================================
//==============================================================================
// TupleRange:
//==============================================================================
//==============================================================================
template <typename ArrayType>
struct UnitTestValueRangeAPI
{
  static constexpr vtk::ComponentIdType NumComps = 3;
  static constexpr vtk::TupleIdType NumTuples = 12;
  static constexpr vtk::ValueIdType NumValues = NumTuples * NumComps;

  void operator()()
  {
    vtkNew<ArrayType> array;
    auto da = static_cast<vtkDataArray*>(array);
    array->SetNumberOfComponents(NumComps);

    this->TestEmptyRange(vtk::DataArrayValueRange(array));
    this->TestEmptyRange(vtk::DataArrayValueRange(da));
    this->TestEmptyRange(vtk::DataArrayValueRange<NumComps>(array));
    this->TestEmptyRange(vtk::DataArrayValueRange<NumComps>(da));

    array->SetNumberOfTuples(this->NumTuples);

    this->TestEmptyRange(vtk::DataArrayValueRange(array, 4, 4));
    this->TestEmptyRange(vtk::DataArrayValueRange(da, 4, 4));
    this->TestEmptyRange(vtk::DataArrayValueRange<NumComps>(array, 4, 4));
    this->TestEmptyRange(vtk::DataArrayValueRange<NumComps>(da, 4, 4));

    FillValueRangeIota(vtk::DataArrayValueRange<NumComps>(array));

    auto pStart = static_cast<vtk::ValueIdType>(NumTuples / 4 * NumComps + 1);
    auto pEnd = static_cast<vtk::ValueIdType>(3 * NumTuples / 4 * NumComps + 2);

    { // Full, dynamic-size, real typed range
      auto range = vtk::DataArrayValueRange(array);
      DispatchRangeTests<ArrayType, vtk::detail::DynamicTupleSize>(range, array, 0, NumValues);
    }
    { // Full, dynamic-size, generic-typed range
      auto range = vtk::DataArrayValueRange(da);
      DispatchRangeTests<vtkDataArray, vtk::detail::DynamicTupleSize>(range, array, 0, NumValues);
    }
    { // Full, fixed-size, real typed range
      auto range = vtk::DataArrayValueRange<NumComps>(array);
      DispatchRangeTests<ArrayType, NumComps>(range, array, 0, NumValues);
    }
    { // Full, fixed-size, generic-typed range
      auto range = vtk::DataArrayValueRange<NumComps>(da);
      DispatchRangeTests<vtkDataArray, NumComps>(range, array, 0, NumValues);
    }
    { // Partial, dynamic-size, real typed range
      auto range = vtk::DataArrayValueRange(array, pStart, pEnd);
      DispatchRangeTests<ArrayType, vtk::detail::DynamicTupleSize>(range, array, pStart, pEnd);
    }
    { // Partial, dynamic-size, generic-typed range
      auto range = vtk::DataArrayValueRange(da, pStart, pEnd);
      DispatchRangeTests<vtkDataArray, vtk::detail::DynamicTupleSize>(range, array, pStart, pEnd);
    }
    { // Partial, fixed-size, real typed range
      auto range = vtk::DataArrayValueRange<NumComps>(array, pStart, pEnd);
      DispatchRangeTests<ArrayType, NumComps>(range, array, pStart, pEnd);
    }
    { // Partial, fixed-size, generic-typed range
      auto range = vtk::DataArrayValueRange<NumComps>(da, pStart, pEnd);
      DispatchRangeTests<vtkDataArray, NumComps>(range, array, pStart, pEnd);
    }
  }

  template <typename Range>
  void TestEmptyRange(Range range)
  {
    for (auto value : range)
    {
      (void)value;
      CHECK_TRUE(false && "This should not execute.");
    }
  }

  template <typename RangeArrayType, vtk::ComponentIdType RangeTupleSize, typename Range>
  void DispatchRangeTests(
    Range range, RangeArrayType* array, vtk::ValueIdType start, vtk::ValueIdType end)
  {
    {
      TestRange<RangeArrayType, RangeTupleSize>(range, array, start, end);
      TestSubRange(range);
      TestDefaultInit(range);
    }

    {
      const Range& crange = range;
      TestRange<RangeArrayType, RangeTupleSize>(crange, array, start, end);
      TestSubRange(crange);
    }
  }

  template <typename RangeArrayType, vtk::ComponentIdType RangeTupleSize, typename Range>
  void TestRange(Range& range, RangeArrayType* array, vtk::ValueIdType start, vtk::ValueIdType end)
  {
    TestTypes<RangeArrayType, RangeTupleSize>(range);

    CHECK_EQUAL(range.GetArray(), array);
    CHECK_EQUAL(range.GetTupleSize(), NumComps);
    CHECK_EQUAL(range.GetBeginValueId(), start);
    CHECK_EQUAL(range.GetEndValueId(), end);
    CHECK_EQUAL(range.size(), end - start);
    CHECK_EQUAL(range.end() - range.begin(), range.size());
    CHECK_EQUAL(range.cend() - range.cbegin(), range.size());
    CHECK_EQUAL_NODUMP(*range.begin(), range[0]);
    CHECK_EQUAL_NODUMP(*(range.begin() + 1), range[1]);

    TestIota(range);
  }

  template <typename RangeArrayType, vtk::ComponentIdType RangeTupleSize, typename Range>
  void TestTypes(Range& range)
  {
    using ConstRange = typename std::add_const<Range>::type;
    using MutableRange = typename std::remove_const<Range>::type;
    (void)range; // decltype doesn't actually count as a usage.

    CHECK_IS_BASE_TYPE_OF(typename Range::ArrayType, RangeArrayType);
    CHECK_TYPEDEF(typename Range::ValueType, vtk::GetAPIType<RangeArrayType>);
    CHECK_TYPEDEF(typename Range::ValueType, vtk::GetAPIType<RangeArrayType>);
    CHECK_TYPEDEF(typename Range::size_type, vtk::ValueIdType);
    CHECK_TYPEDEF(typename Range::size_type, decltype(range.size()));
    CHECK_TYPEDEF(typename Range::iterator, decltype(std::declval<MutableRange>().begin()));
    CHECK_TYPEDEF(typename Range::iterator, decltype(std::declval<MutableRange>().end()));
    CHECK_TYPEDEF(typename Range::const_iterator, decltype(std::declval<ConstRange>().begin()));
    CHECK_TYPEDEF(typename Range::const_iterator, decltype(std::declval<ConstRange>().end()));
    CHECK_TYPEDEF(typename Range::const_iterator, decltype(range.cbegin()));
    CHECK_TYPEDEF(typename Range::const_iterator, decltype(range.cend()));
    CHECK_TYPEDEF(typename Range::reference, decltype(std::declval<MutableRange>()[0]));
    CHECK_TYPEDEF(typename Range::const_reference, decltype(std::declval<ConstRange>()[0]));
    CHECK_TYPEDEF(typename Range::ArrayType, decltype(*range.GetArray()));
    CHECK_TYPEDEF(vtk::ValueIdType, decltype(range.GetBeginValueId()));
    CHECK_TYPEDEF(vtk::ValueIdType, decltype(range.GetEndValueId()));

    static_assert(Range::TupleSizeTag == RangeTupleSize, "Range::TupleSizeTag incorrect.");
  }

  template <typename Range>
  void TestSubRange(Range& range)
  {
    auto range1 = range.GetSubRange(3, 9);
    CHECK_EQUAL(range1.GetBeginValueId(), range.GetBeginValueId() + 3);
    CHECK_EQUAL(range1.GetEndValueId(), range.GetBeginValueId() + 9);
    {
      auto subRange = range1.GetSubRange();
      CHECK_EQUAL(subRange.GetBeginValueId(), range1.GetBeginValueId());
      CHECK_EQUAL(subRange.GetEndValueId(), range1.GetEndValueId());
    }
    {
      auto subRange = range1.GetSubRange(2, 4);
      CHECK_EQUAL(subRange.GetBeginValueId(), range1.GetBeginValueId() + 2);
      CHECK_EQUAL(subRange.GetEndValueId(), range1.GetBeginValueId() + 4);
    }
    {
      auto subRange = range1.GetSubRange(1);
      CHECK_EQUAL(subRange.GetBeginValueId(), range1.GetBeginValueId() + 1);
      CHECK_EQUAL(subRange.GetEndValueId(), range1.GetEndValueId());
    }
    {
      auto subRange = range1.GetSubRange(0, 5);
      CHECK_EQUAL(subRange.GetBeginValueId(), range1.GetBeginValueId());
      CHECK_EQUAL(subRange.GetEndValueId(), range1.GetBeginValueId() + 5);
    }
    {
      auto subRange = range1.GetSubRange(0, 0);
      CHECK_EQUAL(subRange.GetBeginValueId(), range1.GetBeginValueId());
      CHECK_EQUAL(subRange.GetEndValueId(), range1.GetBeginValueId());
    }
  }

  template <typename Range>
  void TestDefaultInit(Range& range)
  {
    auto range1 = Range{};
    range1 = range;
    (void)range;
  }
};

template <typename ArrayType>
struct UnitTestValueIteratorAPI
{
  static constexpr vtk::ComponentIdType NumComps = 3;
  static constexpr vtk::TupleIdType NumTuples = 12;
  static constexpr vtk::ValueIdType NumValues = NumComps * NumTuples;

  void operator()()
  {
    vtkNew<ArrayType> array;
    array->SetNumberOfComponents(NumComps);
    array->SetNumberOfTuples(NumTuples);
    FillValueRangeIota(vtk::DataArrayValueRange<NumComps>(array));

    auto da = static_cast<vtkDataArray*>(array);

    { // Full, dynamic-size, real typed range
      auto range = vtk::DataArrayValueRange(array);
      DispatchRangeTests(range);
    }
    { // Full, dynamic-size, generic-typed range
      auto range = vtk::DataArrayValueRange(da);
      DispatchRangeTests(range);
    }
    { // Full, fixed-size, real typed range
      auto range = vtk::DataArrayValueRange<NumComps>(array);
      DispatchRangeTests(range);
    }
    { // Full, fixed-size, generic-typed range
      auto range = vtk::DataArrayValueRange<NumComps>(da);
      DispatchRangeTests(range);
    }
  }

  template <typename Range>
  void DispatchRangeTests(Range range)
  {
    {
      TestTypes(range);
      TestValueIterator(range);
      TestConstValueIterator(range);
    }

    {
      const Range& crange = range;
      TestTypes(crange);
      TestConstValueIterator(crange);
    }
  }

  template <typename Range>
  void TestTypes(Range& range)
  {
    using Iter = decltype(this->GetTestingIter(range));
    (void)range;

    CHECK_ITER_TYPE(Iter);
    CHECK_TYPEDEF(
      typename std::iterator_traits<Iter>::reference, decltype(std::declval<Iter>()[0]));
  }

  template <typename Range>
  void TestValueIterator(Range& range)
  {
    TestDeref(range);
    TestIndexing(range);
    TestIterSwap(range);
    TestConstCopy(range);
    TestConstAssign(range);
  }

  template <typename Range>
  void TestConstValueIterator(Range& range)
  {
    TestCopy(range);
    TestAssign(range);
    TestTraversal(range);
    TestDerefConst(range);
    TestComparison(range);
    TestIndexingConst(range);
    TestSwap(range);
  }

  template <typename Range>
  void TestCopy(Range& range)
  {
    auto iter = this->GetTestingIter(range);

    using IterType = decltype(iter);
    IterType iter2{ iter };

    CHECK_EQUAL_NODUMP(iter, iter2);
  }

  template <typename Range>
  void TestConstCopy(Range& range)
  {
    // This should only get called with non-const ranges:
    static_assert(!std::is_const<Range>::value, "Expected mutable range.");

    // We should be able to implicitly cast and compare mutable iterators to
    // const ones:
    typename Range::iterator iter{ range.begin() };
    typename Range::const_iterator citer{ iter };
    CHECK_EQUAL_NODUMP(iter, citer);
  }

  template <typename Range>
  void TestAssign(Range& range)
  {
    auto iter = this->GetTestingIter(range);

    auto iter2 = iter + 1;
    auto iter3 = iter + 2;

    CHECK_NOT_EQUAL_NODUMP(iter, iter2);
    CHECK_NOT_EQUAL_NODUMP(iter, iter3);
    CHECK_NOT_EQUAL_NODUMP(iter2, iter3);

    iter2 = iter3 = iter;

    CHECK_EQUAL_NODUMP(iter, iter2);
    CHECK_EQUAL_NODUMP(iter, iter3);
    CHECK_EQUAL_NODUMP(iter2, iter3);
  }

  template <typename Range>
  void TestConstAssign(Range& range)
  {
    // This should only get called with non-const ranges:
    static_assert(!std::is_const<Range>::value, "Expected mutable range.");

    // We should be able to implicitly cast and compare mutable objects to
    // const ones:
    typename Range::iterator iter{ range.begin() };
    typename Range::const_iterator citer{ range.cend() };

    citer = iter;
    CHECK_EQUAL_NODUMP(iter, citer);
  }

  template <typename Range>
  void TestTraversal(Range& range)
  {
    { // operator++ (prefix)
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;
      auto iter3 = ++iter2;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_NOT_EQUAL_NODUMP(iter1, iter3);
      CHECK_EQUAL_NODUMP(iter2, iter3);
      CHECK_EQUAL(iter2 - iter1, 1);
    }

    { // operator++ (postfix)
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;
      auto iter3 = iter2++;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_EQUAL_NODUMP(iter1, iter3);
      CHECK_NOT_EQUAL_NODUMP(iter2, iter3);
      CHECK_EQUAL(iter2 - iter1, 1);
    }

    { // operator-- (prefix)
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;
      auto iter3 = --iter2;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_NOT_EQUAL_NODUMP(iter1, iter3);
      CHECK_EQUAL_NODUMP(iter2, iter3);
      CHECK_EQUAL(iter2 - iter1, -1);
    }

    { // operator-- (postfix)
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;
      auto iter3 = iter2--;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_EQUAL_NODUMP(iter1, iter3);
      CHECK_NOT_EQUAL_NODUMP(iter2, iter3);
      CHECK_EQUAL(iter2 - iter1, -1);
    }

    { // operator +=
      auto iter1 = this->GetTestingIter(range) - 1;
      auto iter2 = iter1 + 2;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_EQUAL(iter2 - iter1, 2);

      iter1 += 2;

      CHECK_EQUAL_NODUMP(iter1, iter2);
    }

    { // operator -=
      auto iter1 = this->GetTestingIter(range) + 1;
      auto iter2 = iter1 - 2;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_EQUAL(iter2 - iter1, -2);

      iter1 -= 2;

      CHECK_EQUAL_NODUMP(iter1, iter2);
    }

    { // operator + (it, off)
      auto iter1 = this->GetTestingIter(range) - 1;
      auto iter2 = iter1 + 2;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_EQUAL(iter2 - iter1, 2);
    }

    { // operator + (off, it)
      auto iter1 = this->GetTestingIter(range) - 1;
      auto iter2 = 2 + iter1;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_EQUAL(iter2 - iter1, 2);
    }

    { // operator - (it, off)
      auto iter1 = this->GetTestingIter(range) + 1;
      auto iter2 = iter1 - 2;

      CHECK_NOT_EQUAL_NODUMP(iter1, iter2);
      CHECK_EQUAL(iter2 - iter1, -2);
    }

    { // operator - (it, it)
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;
      CHECK_EQUAL(iter2 - iter1, 0);

      iter2++;
      CHECK_EQUAL(iter2 - iter1, 1);

      iter2--;
      CHECK_EQUAL(iter2 - iter1, 0);

      --iter2;
      CHECK_EQUAL(iter2 - iter1, -1);

      iter1++;
      CHECK_EQUAL(iter2 - iter1, -2);
    }
  }

  template <typename Range>
  void TestComparison(Range& range)
  {
    { // operator ==
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;

      CHECK_TRUE(iter1 == iter2);
      ++iter2;
      CHECK_FALSE(iter1 == iter2);
    }

    { // operator !=
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;

      CHECK_FALSE(iter1 != iter2);
      ++iter2;
      CHECK_TRUE(iter1 != iter2);
    }

    { // operator <
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1 + 1;

      CHECK_TRUE(iter1 < iter2);
      CHECK_FALSE(iter2 < iter1);
    }

    { // operator >
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1 - 1;

      CHECK_TRUE(iter1 > iter2);
      CHECK_FALSE(iter2 > iter1);
    }

    { // operator <=
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;

      CHECK_TRUE(iter1 <= iter2);
      CHECK_TRUE(iter2 <= iter1);
      ++iter2;
      CHECK_TRUE(iter1 <= iter2);
      CHECK_FALSE(iter2 <= iter1);
    }

    { // operator >=
      auto iter1 = this->GetTestingIter(range);
      auto iter2 = iter1;

      CHECK_TRUE(iter1 >= iter2);
      CHECK_TRUE(iter2 >= iter1);
      --iter2;
      CHECK_TRUE(iter1 >= iter2);
      CHECK_FALSE(iter2 >= iter1);
    }
  }

  template <typename Range>
  void TestDerefConst(Range& range)
  {
    using ValueType = typename Range::ValueType;

    auto start = this->GetTestingIter(range);
    auto end = start + 4;

    ValueType value = *start;
    for (auto it = start; it < end; ++it)
    {
      CHECK_EQUAL(value++, *it);
    }
  }

  template <typename Range>
  void TestDeref(Range& range)
  {
    using ValueType = typename Range::ValueType;

    auto start = this->GetTestingIter(range);
    auto end = start + 4;

    ValueType initialValue = *start;

    for (auto it = start; it < end; ++it)
    {
      *it = 10;
    }

    for (auto it = start; it < end; ++it)
    {
      CHECK_EQUAL(*it, 10);
    }

    // Modifying value types shouldn't modify underlying storage:
    for (auto it = start; it < end; ++it)
    {
      ValueType comp = *it;
      comp = 16;
      (void)comp; // Silence set-but-not-used warning
    }

    for (auto it = start; it < end; ++it)
    {
      CHECK_EQUAL(*it, 10); // Still 10
    }

    // Modifying reference should modify underlying storage:
    for (auto it = start; it < end; ++it)
    {
      using RefType = typename Range::reference;
      RefType comp = *it;
      comp = 16;
    }

    for (auto it = start; it < end; ++it)
    {
      CHECK_EQUAL(*it, 16);
    }

    // Restore:
    for (auto it = start; it < end; ++it)
    {
      *it = initialValue++;
    }
  }

  template <typename Range>
  void TestIndexingConst(Range& range)
  {
    using ValueType = typename Range::value_type;
    using IndexType = typename Range::size_type;

    auto iter = this->GetTestingIter(range);

    ValueType value = *iter;
    for (IndexType i = 0; i < 4; ++i)
    {
      CHECK_EQUAL(value++, iter[i]);
    }
  }

  template <typename Range>
  void TestIndexing(Range& range)
  {
    using IndexType = typename Range::size_type;
    using ValueType = typename Range::value_type;

    auto iter = this->GetTestingIter(range);

    ValueType initialValue = *iter;

    for (IndexType i = 0; i < 4; ++i)
    {
      iter[i] = 19;
    }

    for (auto it = iter; it < iter + 4; ++it)
    {
      CHECK_EQUAL(*it, 19);
    }

    // Restore:
    for (IndexType i = 0; i < 4; ++i)
    {
      iter[i] = initialValue++;
    }
  }

  template <typename Range>
  void TestSwap(Range& range)
  {
    auto iter = this->GetTestingIter(range);
    auto iter1 = iter;
    auto iter2 = iter1 + 1;

    CHECK_TRUE(iter1 < iter2);
    CHECK_FALSE(iter2 < iter1);
    CHECK_TRUE(iter1 + 1 == iter2);
    CHECK_TRUE(iter == iter1);

    {
      // ADL swap:
      using std::swap;
      swap(iter1, iter2);
    }

    CHECK_FALSE(iter1 < iter2);
    CHECK_TRUE(iter2 < iter1);
    CHECK_TRUE(iter2 + 1 == iter1);
    CHECK_TRUE(iter == iter2);

    {
      // ADL swap:
      using std::swap;
      swap(iter1, iter2);
    }

    CHECK_TRUE(iter1 < iter2);
    CHECK_FALSE(iter2 < iter1);
    CHECK_TRUE(iter1 + 1 == iter2);
    CHECK_TRUE(iter == iter1);
  }

  template <typename Range>
  void TestIterSwap(Range& range)
  {
    using ValueType = typename Range::ValueType;

    auto iter = this->GetTestingIter(range);
    auto iter1 = iter;
    auto iter2 = iter1 + 1;

    ValueType val1 = *iter1;
    ValueType val2 = *iter2;

    CHECK_TRUE(iter1 < iter2);
    CHECK_FALSE(iter2 < iter1);
    CHECK_TRUE(iter1 + 1 == iter2);
    CHECK_TRUE(iter == iter1);
    CHECK_EQUAL(val1, *iter1);
    CHECK_EQUAL(val2, *iter2);

    std::iter_swap(iter1, iter2);

    CHECK_TRUE(iter1 < iter2);
    CHECK_FALSE(iter2 < iter1);
    CHECK_TRUE(iter1 + 1 == iter2);
    CHECK_TRUE(iter == iter1);
    CHECK_EQUAL(val1, *iter2);
    CHECK_EQUAL(val2, *iter1);

    std::iter_swap(iter1, iter2);

    CHECK_TRUE(iter1 < iter2);
    CHECK_FALSE(iter2 < iter1);
    CHECK_TRUE(iter1 + 1 == iter2);
    CHECK_TRUE(iter == iter1);
    CHECK_EQUAL(val1, *iter1);
    CHECK_EQUAL(val2, *iter2);
  }

  // Returns an iterator. tupleOffset allows iterators from different tuples to
  // be obtained. The returned iterator +/- 4 are guaranteed valid.
  template <typename Range>
  static auto GetTestingIter(Range& range) -> decltype(range.begin())
  {
    return range.begin() + NumValues / 2;
  }
};

template <typename ArrayType>
struct UnitTestValueReferenceAPI
{
  static constexpr vtk::ComponentIdType NumComps = 9;
  static constexpr vtk::TupleIdType NumTuples = 5;

  void operator()()
  {
    vtkNew<ArrayType> array;
    array->SetNumberOfComponents(NumComps);
    array->SetNumberOfTuples(NumTuples);
    FillValueRangeIota(vtk::DataArrayValueRange<NumComps>(array));

    auto da = static_cast<vtkDataArray*>(array);

    { // Full, dynamic-size, real typed range
      auto range = vtk::DataArrayValueRange(array);
      DispatchRangeTests(range);
    }
    { // Full, dynamic-size, generic-typed range
      auto range = vtk::DataArrayValueRange(da);
      DispatchRangeTests(range);
    }
    { // Full, fixed-size, real typed range
      auto range = vtk::DataArrayValueRange<NumComps>(array);
      DispatchRangeTests(range);
    }
    { // Full, fixed-size, generic-typed range
      auto range = vtk::DataArrayValueRange<NumComps>(da);
      DispatchRangeTests(range);
    }
  }

  template <typename Range>
  void DispatchRangeTests(Range range)
  {
    {
      TestValueReference(range);
      TestConstValueReference(range);
    }

    {
      const Range& crange = range;
      TestConstValueReference(crange);
    }
  }

  template <typename Range>
  void TestValueReference(Range& range)
  {
    TestCopy(range);
    TestAssign(range);
    TestSwap(range);
    TestMath(range);
  }

  template <typename Range>
  void TestConstValueReference(Range& range)
  {
    TestComparison(range);
    TestConstMath(range);
  }

  template <typename Range>
  void TestCopy(Range& range)
  {
    using APIType = typename Range::value_type;
    using RefType = typename Range::reference;

    RefType ref1 = this->GetTestRef(range, 0);
    const APIType val = ref1;

    RefType ref1Copy{ ref1 };
    CHECK_EQUAL_NODUMP(ref1, ref1Copy);
    CHECK_EQUAL_NODUMP(val, ref1Copy);

    ref1Copy = val - 1;
    CHECK_EQUAL_NODUMP(ref1, ref1Copy);
    CHECK_EQUAL_NODUMP(ref1Copy, val - 1);
    CHECK_EQUAL_NODUMP(ref1, val - 1);

    ref1 = val;
    CHECK_EQUAL_NODUMP(ref1, ref1Copy);
    CHECK_EQUAL_NODUMP(ref1Copy, val);
    CHECK_EQUAL_NODUMP(ref1, val);
  }

  template <typename Range>
  void TestAssign(Range& range)
  {
    using APIType = typename Range::value_type;
    using RefType = typename Range::reference;

    RefType ref1 = this->GetTestRef(range, 0);
    const APIType val = ref1;

    RefType ref1Copy{ ref1 };
    CHECK_EQUAL_NODUMP(ref1, ref1Copy);
    CHECK_EQUAL_NODUMP(val, ref1Copy);

    ref1Copy = val - 1;
    CHECK_EQUAL_NODUMP(ref1, ref1Copy);
    CHECK_EQUAL_NODUMP(ref1Copy, val - 1);
    CHECK_EQUAL_NODUMP(ref1, val - 1);

    ref1 = val;
    CHECK_EQUAL_NODUMP(ref1, ref1Copy);
    CHECK_EQUAL_NODUMP(ref1Copy, val);
    CHECK_EQUAL_NODUMP(ref1, val);

    auto ref2 = this->GetTestRef(range, 1);
    CHECK_EQUAL_NODUMP(ref2, val + 1);
    CHECK_NOT_EQUAL_NODUMP(ref1, ref2);
    CHECK_NOT_EQUAL_NODUMP(ref1Copy, ref2);
    CHECK_NOT_EQUAL_NODUMP(val, ref2);

    ref1 = ref2;
    CHECK_EQUAL_NODUMP(ref1, ref2);
    CHECK_EQUAL_NODUMP(ref1Copy, ref2);
    CHECK_EQUAL_NODUMP(ref1, val + 1);
    CHECK_EQUAL_NODUMP(ref1Copy, val + 1);

    ref1 = val;
    CHECK_EQUAL_NODUMP(ref1, ref1Copy);
    CHECK_EQUAL_NODUMP(ref1Copy, val);
    CHECK_EQUAL_NODUMP(ref1, val);
    CHECK_EQUAL_NODUMP(ref2, val + 1);
  }

  template <typename Range>
  void TestSwap(Range& range)
  {
    using APIType = typename Range::value_type;

    auto ref1 = this->GetTestRef(range, 0);
    const APIType val1 = ref1;

    APIType val2 = val1 + 1;

    // ADL swap:
    using std::swap;
    swap(ref1, val2);

    CHECK_EQUAL_NODUMP(ref1, val1 + 1);
    CHECK_EQUAL_NODUMP(val1, val2);

    swap(val2, ref1);

    CHECK_EQUAL_NODUMP(ref1, val1);
    CHECK_EQUAL_NODUMP(val2, val1 + 1);

    auto ref2 = this->GetTestRef(range, 1);
    CHECK_EQUAL_NODUMP(ref2, val2);

    swap(ref1, ref2);

    CHECK_EQUAL_NODUMP(ref1, val2);
    CHECK_EQUAL_NODUMP(ref2, val1);

    swap(ref2, ref1);

    CHECK_EQUAL_NODUMP(ref1, val1);
    CHECK_EQUAL_NODUMP(ref2, val2);
  }

  template <typename Range>
  void TestMath(Range& range)
  {
    // Testing mutable math only. Const math is tested in TestConstMath
    using APIType = typename Range::value_type;
    using RefType = typename Range::reference;

    RefType ref1 = this->GetTestRef(range, 0);
    RefType ref2 = this->GetTestRef(range, 1);
    const APIType val1 = ref1;
    const APIType val2 = ref2;

    const APIType one = static_cast<APIType>(1);
    const APIType two = static_cast<APIType>(2);
    const APIType bignum = static_cast<APIType>(120); // must fit in int8

    // +=
    {
      auto v = (ref1 += one);
      CHECK_EQUAL_NODUMP(ref1, v);
      CHECK_EQUAL_NODUMP(ref1, val1 + one);
      ref1 = val1;
    }
    {
      APIType tmp = one;
      auto v = (tmp += ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(tmp, val1 + one);
      CHECK_EQUAL_NODUMP(v, val1 + one);
    }
    {
      auto v = (ref1 += ref2);
      CHECK_EQUAL_NODUMP(ref1, val1 + val2);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_EQUAL_NODUMP(v, val1 + val2);
      ref1 = val1;
    }

    // -=
    {
      auto v = (ref1 -= one);
      CHECK_EQUAL_NODUMP(ref1, v);
      CHECK_EQUAL_NODUMP(ref1, val1 - one);
      ref1 = val1;
    }
    {
      APIType tmp = bignum;
      auto v = (tmp -= ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(tmp, bignum - val1);
      CHECK_EQUAL_NODUMP(v, bignum - val1);
    }
    {
      auto v = (ref1 -= ref2);
      CHECK_EQUAL_NODUMP(ref1, val1 - val2);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_EQUAL_NODUMP(v, val1 - val2);
      ref1 = val1;
    }

    // *=
    {
      auto v = (ref1 *= two);
      CHECK_EQUAL_NODUMP(ref1, v);
      CHECK_EQUAL_NODUMP(ref1, val1 * two);
      ref1 = val1;
    }
    {
      APIType tmp = two;
      auto v = (tmp *= ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(tmp, val1 * two);
      CHECK_EQUAL_NODUMP(v, val1 * two);
    }
    {
      auto v = (ref1 *= ref2);
      CHECK_EQUAL_NODUMP(ref1, val1 * val2);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_EQUAL_NODUMP(v, val1 * val2);
      ref1 = val1;
    }

    // /=
    {
      auto v = (ref1 /= two);
      CHECK_EQUAL_NODUMP(ref1, v);
      CHECK_EQUAL_NODUMP(ref1, val1 / two);
      ref1 = val1;
    }
    {
      APIType tmp = bignum;
      auto v = (tmp /= ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(tmp, bignum / val1);
      CHECK_EQUAL_NODUMP(v, bignum / val1);
    }
    {
      auto v = (ref1 /= ref2);
      // Use a tolerance test to account for rounding errors.
      CHECK_TRUE(std::fabs(ref1 - APIType{ val1 / val2 }) < 1e-5);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_TRUE(std::fabs(v - APIType{ val1 / val2 }) < 1e-5);
      ref1 = val1;
    }

    // ++ (pre)
    {
      auto v = ++ref1;
      CHECK_EQUAL_NODUMP(ref1, val1 + one);
      CHECK_EQUAL_NODUMP(v, val1 + one);
      ref1 = val1;
    }

    // ++ (post)
    {
      auto v = ref1++;
      CHECK_EQUAL_NODUMP(ref1, val1 + one);
      CHECK_EQUAL_NODUMP(v, val1);
      ref1 = val1;
    }

    // -- (pre)
    {
      auto v = --ref1;
      CHECK_EQUAL_NODUMP(ref1, val1 - one);
      CHECK_EQUAL_NODUMP(v, val1 - one);
      ref1 = val1;
    }

    // -- (post)
    {
      auto v = ref1--;
      CHECK_EQUAL_NODUMP(ref1, val1 - one);
      CHECK_EQUAL_NODUMP(v, val1);
      ref1 = val1;
    }
  }

  template <typename Range>
  void TestComparison(Range& range)
  {
    using APIType = typename Range::value_type;

    auto ref1 = this->GetTestRef(range, 0);
    auto refTmp = this->GetTestRef(range, 0); // same as ref1
    auto ref2 = this->GetTestRef(range, 1);
    const APIType val1 = ref1;
    const APIType val2 = ref2;

    const APIType one = static_cast<APIType>(1);
    const APIType bignum = static_cast<APIType>(120); // must fit in int8

    // ==
    CHECK_TRUE(ref1 == val1);
    CHECK_TRUE(ref1 == refTmp);
    CHECK_FALSE(ref1 == val2);
    CHECK_FALSE(ref2 == refTmp);

    // !=
    CHECK_FALSE(ref1 != val1);
    CHECK_FALSE(ref1 != refTmp);
    CHECK_TRUE(ref1 != val2);
    CHECK_TRUE(ref2 != refTmp);

    // <
    CHECK_TRUE(ref1 < bignum);
    CHECK_TRUE(one < ref1);
    CHECK_TRUE(ref1 < ref2);
    CHECK_TRUE(refTmp < ref2);
    CHECK_FALSE(bignum < ref1);
    CHECK_FALSE(ref1 < one);
    CHECK_FALSE(ref2 < ref1);
    CHECK_FALSE(ref2 < refTmp);
    CHECK_FALSE(ref1 < refTmp);
    CHECK_FALSE(ref1 < val1);
    CHECK_FALSE(val1 < ref1);

    // >
    CHECK_FALSE(ref1 > bignum);
    CHECK_FALSE(one > ref1);
    CHECK_FALSE(ref1 > ref2);
    CHECK_FALSE(refTmp > ref2);
    CHECK_TRUE(bignum > ref1);
    CHECK_TRUE(ref1 > one);
    CHECK_TRUE(ref2 > ref1);
    CHECK_TRUE(ref2 > refTmp);
    CHECK_FALSE(ref1 > refTmp);
    CHECK_FALSE(ref1 > val1);
    CHECK_FALSE(val1 > ref1);

    // <=
    CHECK_TRUE(ref1 <= bignum);
    CHECK_TRUE(one <= ref1);
    CHECK_TRUE(ref1 <= ref2);
    CHECK_TRUE(refTmp <= ref2);
    CHECK_FALSE(bignum <= ref1);
    CHECK_FALSE(ref1 <= one);
    CHECK_FALSE(ref2 <= ref1);
    CHECK_FALSE(ref2 <= refTmp);
    CHECK_TRUE(ref1 <= refTmp);
    CHECK_TRUE(ref1 <= val1);
    CHECK_TRUE(val1 <= ref1);

    // >=
    CHECK_FALSE(ref1 >= bignum);
    CHECK_FALSE(one >= ref1);
    CHECK_FALSE(ref1 >= ref2);
    CHECK_FALSE(refTmp >= ref2);
    CHECK_TRUE(bignum >= ref1);
    CHECK_TRUE(ref1 >= one);
    CHECK_TRUE(ref2 >= ref1);
    CHECK_TRUE(ref2 >= refTmp);
    CHECK_TRUE(ref1 >= refTmp);
    CHECK_TRUE(ref1 >= val1);
    CHECK_TRUE(val1 >= ref1);
  }

  template <typename Range>
  void TestConstMath(Range& range)
  {
    // Testing const math only. Mutable math is tested in TestMath
    using APIType = typename Range::value_type;
    using CRefType = typename Range::const_reference;

    const CRefType ref1 = this->GetTestRef(range, 0);
    const CRefType ref2 = this->GetTestRef(range, 1);
    const APIType val1 = ref1;
    const APIType val2 = ref2;

    const APIType one = static_cast<APIType>(1);
    const APIType two = static_cast<APIType>(2);
    const APIType bignum = static_cast<APIType>(120); // must fit in int8

    // +
    {
      auto v = (ref1 + one);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, val1 + one);
    }
    {
      auto v = (one + ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, val1 + one);
    }
    {
      auto v = (ref1 + ref2);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_EQUAL_NODUMP(v, val1 + val2);
    }

    // -
    {
      auto v = (ref1 - one);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, val1 - one);
    }
    {
      auto v = (bignum - ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, bignum - val1);
    }
    {
      auto v = (ref1 - ref2);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_EQUAL_NODUMP(v, val1 - val2);
    }

    // *
    {
      auto v = (ref1 * two);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, val1 * two);
    }
    {
      auto v = (two * ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, val1 * two);
    }
    {
      auto v = (ref1 * ref2);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_EQUAL_NODUMP(v, val1 * val2);
    }

    // /
    {
      auto v = (ref1 / two);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, val1 / two);
    }
    {
      auto v = (bignum / ref1);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(v, bignum / val1);
    }
    {
      auto v = (ref1 / ref2);
      CHECK_EQUAL_NODUMP(ref1, val1);
      CHECK_EQUAL_NODUMP(ref2, val2);
      CHECK_EQUAL_NODUMP(v, val1 / val2);
    }
  }

  // Return a reference. Valid offsets range from (-4, 4), and
  // values increase with offset.
  template <typename Range>
  auto GetTestRef(Range& range, vtk::ValueIdType offset) -> decltype(std::declval<Range>()[0])
  {
    assert(offset >= -4 && offset <= 4);
    return range[6 + offset];
  }
};

struct UnitTestEdgeCases
{
  static constexpr vtk::ComponentIdType NumComps = 3;
  static constexpr vtk::TupleIdType NumTuples = 12;

  void operator()()
  {
    TestSpecializations();

    std::cerr << "SOA<float> <--> AOS<float>\n";
    DispatchValueCompat<vtkSOADataArrayTemplate<float>, vtkAOSDataArrayTemplate<float>>();

    std::cerr << "AOS<float> <--> SOA<float>\n";
    DispatchValueCompat<vtkAOSDataArrayTemplate<float>, vtkSOADataArrayTemplate<float>>();

    std::cerr << "SOA<double> <--> AOS<float>\n";
    DispatchValueCompat<vtkSOADataArrayTemplate<double>, vtkAOSDataArrayTemplate<float>>();

    std::cerr << "AOS<float> <--> SOA<double>\n";
    DispatchValueCompat<vtkAOSDataArrayTemplate<float>, vtkSOADataArrayTemplate<double>>();

    std::cerr << "SOA<int> <--> AOS<float>\n";
    DispatchValueCompat<vtkSOADataArrayTemplate<int>, vtkAOSDataArrayTemplate<float>>();

    std::cerr << "AOS<float> <--> SOA<int>\n";
    DispatchValueCompat<vtkAOSDataArrayTemplate<float>, vtkSOADataArrayTemplate<int>>();

#ifdef VTK_USE_SCALED_SOA_ARRAYS
    std::cerr << "ScaleSOA<float> <--> AOS<float>\n";
    DispatchValueCompat<vtkScaledSOADataArrayTemplate<float>, vtkAOSDataArrayTemplate<float>>();

    std::cerr << "AOS<float> <--> ScaleSOA<float>\n";
    DispatchValueCompat<vtkAOSDataArrayTemplate<float>, vtkScaledSOADataArrayTemplate<float>>();

    std::cerr << "ScaleSOA<double> <--> AOS<float>\n";
    DispatchValueCompat<vtkScaledSOADataArrayTemplate<double>, vtkAOSDataArrayTemplate<float>>();

    std::cerr << "AOS<float> <--> ScaleSOA<double>\n";
    DispatchValueCompat<vtkAOSDataArrayTemplate<float>, vtkScaledSOADataArrayTemplate<double>>();

    std::cerr << "ScaleSOA<int> <--> AOS<float>\n";
    DispatchValueCompat<vtkScaledSOADataArrayTemplate<int>, vtkAOSDataArrayTemplate<float>>();

    std::cerr << "AOS<float> <--> ScaleSOA<int>\n";
    DispatchValueCompat<vtkAOSDataArrayTemplate<float>, vtkScaledSOADataArrayTemplate<int>>();
#endif
  }

  static void TestSpecializations()
  {
    // Specializations are disabled when iterator debugging is enabled:
#ifndef VTK_DEBUG_RANGE_ITERATORS
    // These should use the objects in vtkDataArrayTupleRange_AOS.h, which
    // end up using ValueType* pointers for component iterators.
    TestAOSSpecialization<vtkAOSDataArrayTemplate<float>>();
    TestAOSSpecialization<vtkFloatArray>();
#endif
  }

#ifndef VTK_DEBUG_RANGE_ITERATORS
  template <typename ArrayType>
  static void TestAOSSpecialization()
  {
    using ValueType = vtk::GetAPIType<ArrayType>;
    using RangeType = decltype(vtk::DataArrayValueRange(std::declval<ArrayType*>()));
    using ValueIterType = decltype(std::declval<RangeType>().begin());

    // Sanity Check:
    static_assert(vtk::IsAOSDataArray<ArrayType>::value, "Not AOS type?");

    // Ensure that iterator type is just a pointer:
    static_assert(std::is_same<ValueType*, typename std::decay<ValueIterType>::type>::value,
      "AOS specialization not used!");
  }
#endif

  template <typename ArrayType>
  static void PrepArray(ArrayType* array)
  {
    array->SetNumberOfComponents(NumComps);
    array->SetNumberOfTuples(NumTuples);
    FillValueRangeIota(vtk::DataArrayValueRange<NumComps>(array));
  }

  template <typename ArrayT1, typename ArrayT2>
  void DispatchValueCompat()
  {
    vtkNew<ArrayT1> storage1;
    vtkNew<ArrayT2> storage2;
    this->PrepArray(static_cast<ArrayT1*>(storage1));
    this->PrepArray(static_cast<ArrayT2*>(storage2));

    ArrayT1* a1 = storage1;
    ArrayT2* a2 = storage2;
    vtkDataArray* da1 = a1;
    vtkDataArray* da2 = a2;

    // Generate ranges:
    // - derived and vtkDataArray pointers
    // - dynamic and fixed tuple sizes
    // - mutable and const tuple sizes

    auto aRange1 = vtk::DataArrayValueRange(a1);
    auto aRange2 = vtk::DataArrayValueRange(a2);
    auto daRange1 = vtk::DataArrayValueRange(da1);
    auto daRange2 = vtk::DataArrayValueRange(da2);

    auto aFixedRange1 = vtk::DataArrayValueRange<NumComps>(a1);
    auto aFixedRange2 = vtk::DataArrayValueRange<NumComps>(a2);
    auto daFixedRange1 = vtk::DataArrayValueRange<NumComps>(da1);
    auto daFixedRange2 = vtk::DataArrayValueRange<NumComps>(da2);

    using ARange1Type = decltype(aRange1);
    using ARange2Type = decltype(aRange2);
    using DARange1Type = decltype(daRange1);
    using DARange2Type = decltype(daRange2);

    using AFixedRange1Type = decltype(aFixedRange1);
    using AFixedRange2Type = decltype(aFixedRange2);
    using DAFixedRange1Type = decltype(daFixedRange1);
    using DAFixedRange2Type = decltype(daFixedRange2);

    const ARange1Type caRange1 = aRange1;
    const ARange2Type caRange2 = aRange2;
    const DARange1Type cdaRange1 = daRange1;
    const DARange2Type cdaRange2 = daRange2;

    const AFixedRange1Type caFixedRange1 = aFixedRange1;
    const AFixedRange2Type caFixedRange2 = aFixedRange2;
    const DAFixedRange1Type cdaFixedRange1 = daFixedRange1;
    const DAFixedRange2Type cdaFixedRange2 = daFixedRange2;

    this->LaunchTests(aRange1, aRange2);
    this->LaunchTests(aRange1, daRange2);
    this->LaunchTests(aRange1, aFixedRange2);
    this->LaunchTests(aRange1, daFixedRange2);
    this->LaunchTests(aRange1, caRange2);
    this->LaunchTests(aRange1, cdaRange2);
    this->LaunchTests(aRange1, caFixedRange2);
    this->LaunchTests(aRange1, cdaFixedRange2);
    this->LaunchTests(daRange1, aRange2);
    this->LaunchTests(daRange1, daRange2);
    this->LaunchTests(daRange1, aFixedRange2);
    this->LaunchTests(daRange1, daFixedRange2);
    this->LaunchTests(daRange1, caRange2);
    this->LaunchTests(daRange1, cdaRange2);
    this->LaunchTests(daRange1, caFixedRange2);
    this->LaunchTests(daRange1, cdaFixedRange2);
    this->LaunchTests(aFixedRange1, aRange2);
    this->LaunchTests(aFixedRange1, daRange2);
    this->LaunchTests(aFixedRange1, aFixedRange2);
    this->LaunchTests(aFixedRange1, daFixedRange2);
    this->LaunchTests(aFixedRange1, caRange2);
    this->LaunchTests(aFixedRange1, cdaRange2);
    this->LaunchTests(aFixedRange1, caFixedRange2);
    this->LaunchTests(aFixedRange1, cdaFixedRange2);
    this->LaunchTests(daFixedRange1, aRange2);
    this->LaunchTests(daFixedRange1, daRange2);
    this->LaunchTests(daFixedRange1, aFixedRange2);
    this->LaunchTests(daFixedRange1, daFixedRange2);
    this->LaunchTests(daFixedRange1, caRange2);
    this->LaunchTests(daFixedRange1, cdaRange2);
    this->LaunchTests(daFixedRange1, caFixedRange2);
    this->LaunchTests(daFixedRange1, cdaFixedRange2);
    this->LaunchTests(caRange1, aRange2);
    this->LaunchTests(caRange1, daRange2);
    this->LaunchTests(caRange1, aFixedRange2);
    this->LaunchTests(caRange1, daFixedRange2);
    this->LaunchTests(caRange1, caRange2);
    this->LaunchTests(caRange1, cdaRange2);
    this->LaunchTests(caRange1, caFixedRange2);
    this->LaunchTests(caRange1, cdaFixedRange2);
    this->LaunchTests(cdaRange1, aRange2);
    this->LaunchTests(cdaRange1, daRange2);
    this->LaunchTests(cdaRange1, aFixedRange2);
    this->LaunchTests(cdaRange1, daFixedRange2);
    this->LaunchTests(cdaRange1, caRange2);
    this->LaunchTests(cdaRange1, cdaRange2);
    this->LaunchTests(cdaRange1, caFixedRange2);
    this->LaunchTests(cdaRange1, cdaFixedRange2);
    this->LaunchTests(caFixedRange1, aRange2);
    this->LaunchTests(caFixedRange1, daRange2);
    this->LaunchTests(caFixedRange1, aFixedRange2);
    this->LaunchTests(caFixedRange1, daFixedRange2);
    this->LaunchTests(caFixedRange1, caRange2);
    this->LaunchTests(caFixedRange1, cdaRange2);
    this->LaunchTests(caFixedRange1, caFixedRange2);
    this->LaunchTests(caFixedRange1, cdaFixedRange2);
    this->LaunchTests(cdaFixedRange1, aRange2);
    this->LaunchTests(cdaFixedRange1, daRange2);
    this->LaunchTests(cdaFixedRange1, aFixedRange2);
    this->LaunchTests(cdaFixedRange1, daFixedRange2);
    this->LaunchTests(cdaFixedRange1, caRange2);
    this->LaunchTests(cdaFixedRange1, cdaRange2);
    this->LaunchTests(cdaFixedRange1, caFixedRange2);
    this->LaunchTests(cdaFixedRange1, cdaFixedRange2);
  }

  template <typename Range>
  using IsConst = std::is_const<Range>;

  template <typename Range>
  using IsMutable = std::integral_constant<bool, !IsConst<Range>::value>;

  template <typename R1, typename R2>
  using SameValueType = std::integral_constant<bool,
    std::is_same<typename R1::value_type, typename R2::value_type>::value>;

  template <typename Range1, typename Range2>
  using IsSwappable = std::integral_constant<bool,
    (SameValueType<Range1, Range2>::value && IsMutable<Range1>::value && IsMutable<Range2>::value)>;

  template <typename Range1, typename Range2>
  using IsNotSwappable = std::integral_constant<bool, !IsSwappable<Range1, Range2>::value>;

  template <typename Range, typename T = void>
  using EnableIfRangeIsConst = typename std::enable_if<IsConst<Range>::value, T>::type;

  template <typename Range, typename T = void>
  using EnableIfRangeIsMutable = typename std::enable_if<IsMutable<Range>::value, T>::type;

  template <typename Range1, typename Range2, typename T = void>
  using EnableIfSameValueType =
    typename std::enable_if<SameValueType<Range1, Range2>::value, T>::type;

  template <typename Range1, typename Range2, typename T = void>
  using EnableIfSwappable = typename std::enable_if<IsSwappable<Range1, Range2>::value, T>::type;

  template <typename Range1, typename Range2, typename T = void>
  using EnableIfNotSwappable =
    typename std::enable_if<IsNotSwappable<Range1, Range2>::value, T>::type;

  // range1 is const:
  template <typename Range1, typename Range2>
  void LaunchTests(Range1& r1, Range2& r2, EnableIfRangeIsConst<Range1, void*> = nullptr)
  {
    this->TestValueCompare(r1, r2);
  }

  // range1 is not const:
  template <typename Range1, typename Range2>
  void LaunchTests(Range1& r1, Range2& r2, EnableIfRangeIsMutable<Range1, void*> = nullptr)
  {
    this->TestValueAssign(r1, r2);
    this->TestValueCompare(r1, r2);
    this->TestValueSwap(r1, r2);
  }

  template <typename Range1, typename Range2>
  void TestValueAssign(Range1& r1, Range2& r2)
  {
    static_assert(IsMutable<Range1>{}, "r1 must be mutable.");

    auto start1 = r1.begin() + 2;
    auto end1 = start1 + 4;
    auto start2 = r2.begin() + 6;
    auto end2 = start2 + 4;

    auto data1 = this->StoreRange(start1, end1);
    auto data2 = this->StoreRange(start2, end2);

    CHECK_FALSE(this->CompareRange(start1, end1, data2));

    auto iter2 = start2;
    for (auto it = start1; it < end1; ++it)
    {
      *it = *iter2++;
    }

    CHECK_TRUE(this->CompareRange(start1, end1, data2));
    CHECK_TRUE(this->CompareRange(start2, end2, data2));

    this->RestoreRange(start1, end1, data1);
  }

  template <typename Range1, typename Range2>
  void TestValueCompare(Range1& r1, Range2& r2)
  {

    auto iter1 = r1.begin() + 7;
    auto iter2 = r2.begin() + 7;

    CHECK_TRUE(*iter1 == *iter2);
    CHECK_FALSE(*iter1 != *iter2);
    CHECK_FALSE(*iter1 < *iter2);
    CHECK_FALSE(*iter1 > *iter2);
    CHECK_TRUE(*iter1 <= *iter2);
    CHECK_TRUE(*iter1 >= *iter2);

    ++iter2;

    CHECK_FALSE(*iter1 == *iter2);
    CHECK_TRUE(*iter1 != *iter2);
    CHECK_TRUE(*iter1 < *iter2);
    CHECK_FALSE(*iter1 > *iter2);
    CHECK_TRUE(*iter1 <= *iter2);
    CHECK_FALSE(*iter1 >= *iter2);

    iter1 += 2;

    CHECK_FALSE(*iter1 == *iter2);
    CHECK_TRUE(*iter1 != *iter2);
    CHECK_FALSE(*iter1 < *iter2);
    CHECK_TRUE(*iter1 > *iter2);
    CHECK_FALSE(*iter1 <= *iter2);
    CHECK_TRUE(*iter1 >= *iter2);
  }

  template <typename Range1, typename Range2>
  EnableIfNotSwappable<Range1, Range2, void> TestValueSwap(Range1&, Range2&)
  {
    // no-op, ranges aren't swappable.
  }

  template <typename Range1, typename Range2>
  EnableIfSwappable<Range1, Range2, void> TestValueSwap(Range1& r1, Range2& r2)
  {
    static_assert(SameValueType<Range1, Range2>::value, "Mismatched value_types.");
    static_assert(IsMutable<Range1>::value, "r1 must be mutable.");
    static_assert(IsMutable<Range2>::value, "r2 must be mutable.");

    auto start1 = r1.begin() + 2;
    auto end1 = start1 + 4;
    auto start2 = r2.begin() + 6;
    auto end2 = start2 + 4;

    auto data1 = this->StoreRange(start1, end1);
    auto data2 = this->StoreRange(start2, end2);

    CHECK_TRUE(this->CompareRange(start1, end1, data1));
    CHECK_TRUE(this->CompareRange(start2, end2, data2));
    CHECK_TRUE(this->CompareRange(r1.begin() + 2, r1.begin() + 6, data1));
    CHECK_TRUE(this->CompareRange(r2.begin() + 6, r2.begin() + 10, data2));

    CHECK_FALSE(this->CompareRange(start1, end1, data2));
    CHECK_FALSE(this->CompareRange(start2, end2, data1));
    CHECK_FALSE(this->CompareRange(r1.begin() + 2, r1.begin() + 6, data2));
    CHECK_FALSE(this->CompareRange(r2.begin() + 6, r2.begin() + 10, data1));

    {
      auto it2 = start2;
      for (auto it1 = start1; it1 < end1; ++it1)
      {
        // ADL swap:
        using std::swap;
        swap(*it1, *it2++);
      }
      CHECK_TRUE(it2 == end2);
    }

    CHECK_TRUE(this->CompareRange(start1, end1, data2));
    CHECK_TRUE(this->CompareRange(r1.begin() + 2, r1.begin() + 6, data2));
    CHECK_TRUE(this->CompareRange(start2, end2, data1));
    CHECK_TRUE(this->CompareRange(r2.begin() + 6, r2.begin() + 10, data1));

    {
      auto it2 = start2;
      for (auto it1 = start1; it1 < end1; ++it1)
      {
        std::iter_swap(it1, it2++);
      }
      CHECK_TRUE(it2 == end2);
    }

    CHECK_TRUE(this->CompareRange(start1, end1, data1));
    CHECK_TRUE(this->CompareRange(r1.begin() + 2, r1.begin() + 6, data1));
    CHECK_TRUE(this->CompareRange(start2, end2, data2));
    CHECK_TRUE(this->CompareRange(r2.begin() + 6, r2.begin() + 10, data2));

    this->RestoreRange(start1, end1, data1);
    this->RestoreRange(start2, end2, data2);
  }

  template <typename IterType>
  static auto StoreRange(IterType start, IterType end)
    -> std::vector<typename std::iterator_traits<IterType>::value_type>
  {
    using T = typename std::iterator_traits<IterType>::value_type;
    return std::vector<T>{ start, end };
  }

  template <typename IterType, typename VectorType>
  static void RestoreRange(IterType start, IterType end, const VectorType& data)
  {
    static_assert(std::is_same<typename std::iterator_traits<IterType>::value_type,
                    typename VectorType::value_type>::value,
      "Mismatched value types.");
    CHECK_EQUAL(data.size(), static_cast<size_t>(end - start));
    std::copy(data.begin(), data.end(), start);
  }

  template <typename IterType, typename VectorType>
  static bool CompareRange(IterType start, IterType end, const VectorType& data)
  {
    static_assert(std::is_convertible<typename std::iterator_traits<IterType>::value_type,
                    typename VectorType::value_type>::value,
      "Mismatched value types.");

    return static_cast<std::size_t>(end - start) == data.size() &&
      std::equal(data.begin(), data.end(), start);
  }
};

template <typename ArrayType>
void RunTestsForArray()
{
  std::cerr << "ValueRangeAPI:\n";
  UnitTestValueRangeAPI<ArrayType>{}();
  std::cerr << "ValueIteratorAPI:\n";
  UnitTestValueIteratorAPI<ArrayType>{}();
  std::cerr << "ValueReferenceAPI:\n";
  UnitTestValueReferenceAPI<ArrayType>{}();
}

} // end anon namespace

int TestDataArrayValueRange(int, char*[])
{
  std::cerr << "AOS:\n";
  RunTestsForArray<vtkAOSDataArrayTemplate<float>>();
  std::cerr << "SOA:\n";
  RunTestsForArray<vtkSOADataArrayTemplate<float>>();
#ifdef VTK_USE_SCALED_SOA_ARRAYS
  std::cerr << "ScaleSOA:\n";
  RunTestsForArray<vtkScaledSOADataArrayTemplate<float>>();
#endif
  std::cerr << "vtkFloatArray:\n";
  RunTestsForArray<vtkFloatArray>();

  std::cerr << "\nEdgeCases:\n";
  UnitTestEdgeCases{}();

  return NumErrors != 0;
}