add gsl::index typedef (#620)

* rename index in multi_span to span_index

gsl::index is name reserved for different type

* add gsl::index typedef

cppcoreguidelines referece: ES.107: Don't use unsigned for subscripts, prefer gsl::index

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-subscripts

* rename span_index to multi_span_index

6 files changed, 137 insertions, 127 deletions

diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index b048a43..1aa8ba6 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -43,6 +43,9 @@ namespace gsl
 // GSL.util: utilities
 //
 
+// index type for all container indexes/subscripts/sizes
+using index = std::ptrdiff_t;
+
 // final_action allows you to ensure something gets run at the end of a scope
 template <class F>
 class final_action
@@ -117,25 +120,25 @@ T narrow(U u)
 // at() - Bounds-checked way of accessing builtin arrays, std::array, std::vector
 //
 template <class T, std::size_t N>
-constexpr T& at(T (&arr)[N], const std::ptrdiff_t index)
+constexpr T& at(T (&arr)[N], const index i)
 {
-    Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(N));
-    return arr[static_cast<std::size_t>(index)];
+    Expects(i >= 0 && i < narrow_cast<index>(N));
+    return arr[static_cast<std::size_t>(i)];
 }
 
 template <class Cont>
-constexpr auto at(Cont& cont, const std::ptrdiff_t index) -> decltype(cont[cont.size()])
+constexpr auto at(Cont& cont, const index i) -> decltype(cont[cont.size()])
 {
-    Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(cont.size()));
+    Expects(i >= 0 && i < narrow_cast<index>(cont.size()));
     using size_type = decltype(cont.size());
-    return cont[static_cast<size_type>(index)];
+    return cont[static_cast<size_type>(i)];
 }
 
 template <class T>
-constexpr T at(const std::initializer_list<T> cont, const std::ptrdiff_t index)
+constexpr T at(const std::initializer_list<T> cont, const index i)
 {
-    Expects(index >= 0 && index < narrow_cast<std::ptrdiff_t>(cont.size()));
-    return *(cont.begin() + index);
+    Expects(i >= 0 && i < narrow_cast<index>(cont.size()));
+    return *(cont.begin() + i);
 }
 
 } // namespace gsl
diff --git a/include/gsl/multi_span b/include/gsl/multi_span
index cf82144..65e65a1 100644
--- a/include/gsl/multi_span
+++ b/include/gsl/multi_span
@@ -85,12 +85,12 @@ namespace details
 }
 
 template <std::size_t Rank>
-class index final
+class multi_span_index final
 {
     static_assert(Rank > 0, "Rank must be greater than 0!");
 
     template <std::size_t OtherRank>
-    friend class index;
+    friend class multi_span_index;
 
 public:
     static const std::size_t rank = Rank;
@@ -99,22 +99,22 @@ public:
     using reference = std::add_lvalue_reference_t<value_type>;
     using const_reference = std::add_lvalue_reference_t<std::add_const_t<value_type>>;
 
-    constexpr index() GSL_NOEXCEPT {}
+    constexpr multi_span_index() GSL_NOEXCEPT {}
 
-    constexpr index(const value_type (&values)[Rank]) GSL_NOEXCEPT
+    constexpr multi_span_index(const value_type (&values)[Rank]) GSL_NOEXCEPT
     {
         std::copy(values, values + Rank, elems);
     }
 
     template <typename... Ts, typename = std::enable_if_t<(sizeof...(Ts) == Rank) &&
                                                           details::are_integral<Ts...>::value>>
-    constexpr index(Ts... ds) GSL_NOEXCEPT : elems{narrow_cast<value_type>(ds)...}
+    constexpr multi_span_index(Ts... ds) GSL_NOEXCEPT : elems{narrow_cast<value_type>(ds)...}
     {
     }
 
-    constexpr index(const index& other) GSL_NOEXCEPT = default;
+    constexpr multi_span_index(const multi_span_index& other) GSL_NOEXCEPT = default;
 
-    constexpr index& operator=(const index& rhs) GSL_NOEXCEPT = default;
+    constexpr multi_span_index& operator=(const multi_span_index& rhs) GSL_NOEXCEPT = default;
 
     // Preconditions: component_idx < rank
     constexpr reference operator[](std::size_t component_idx)
@@ -130,75 +130,75 @@ public:
         return elems[component_idx];
     }
 
-    constexpr bool operator==(const index& rhs) const GSL_NOEXCEPT
+    constexpr bool operator==(const multi_span_index& rhs) const GSL_NOEXCEPT
     {
         return std::equal(elems, elems + rank, rhs.elems);
     }
 
-    constexpr bool operator!=(const index& rhs) const GSL_NOEXCEPT { return !(*this == rhs); }
+    constexpr bool operator!=(const multi_span_index& rhs) const GSL_NOEXCEPT { return !(*this == rhs); }
 
-    constexpr index operator+() const GSL_NOEXCEPT { return *this; }
+    constexpr multi_span_index operator+() const GSL_NOEXCEPT { return *this; }
 
-    constexpr index operator-() const GSL_NOEXCEPT
+    constexpr multi_span_index operator-() const GSL_NOEXCEPT
     {
-        index ret = *this;
+        multi_span_index ret = *this;
         std::transform(ret, ret + rank, ret, std::negate<value_type>{});
         return ret;
     }
 
-    constexpr index operator+(const index& rhs) const GSL_NOEXCEPT
+    constexpr multi_span_index operator+(const multi_span_index& rhs) const GSL_NOEXCEPT
     {
-        index ret = *this;
+        multi_span_index ret = *this;
         ret += rhs;
         return ret;
     }
 
-    constexpr index operator-(const index& rhs) const GSL_NOEXCEPT
+    constexpr multi_span_index operator-(const multi_span_index& rhs) const GSL_NOEXCEPT
     {
-        index ret = *this;
+        multi_span_index ret = *this;
         ret -= rhs;
         return ret;
     }
 
-    constexpr index& operator+=(const index& rhs) GSL_NOEXCEPT
+    constexpr multi_span_index& operator+=(const multi_span_index& rhs) GSL_NOEXCEPT
     {
         std::transform(elems, elems + rank, rhs.elems, elems, std::plus<value_type>{});
         return *this;
     }
 
-    constexpr index& operator-=(const index& rhs) GSL_NOEXCEPT
+    constexpr multi_span_index& operator-=(const multi_span_index& rhs) GSL_NOEXCEPT
     {
         std::transform(elems, elems + rank, rhs.elems, elems, std::minus<value_type>{});
         return *this;
     }
 
-    constexpr index operator*(value_type v) const GSL_NOEXCEPT
+    constexpr multi_span_index operator*(value_type v) const GSL_NOEXCEPT
     {
-        index ret = *this;
+        multi_span_index ret = *this;
         ret *= v;
         return ret;
     }
 
-    constexpr index operator/(value_type v) const GSL_NOEXCEPT
+    constexpr multi_span_index operator/(value_type v) const GSL_NOEXCEPT
     {
-        index ret = *this;
+        multi_span_index ret = *this;
         ret /= v;
         return ret;
     }
 
-    friend constexpr index operator*(value_type v, const index& rhs) GSL_NOEXCEPT
+    friend constexpr multi_span_index operator*(value_type v, const multi_span_index& rhs) GSL_NOEXCEPT
     {
         return rhs * v;
     }
 
-    constexpr index& operator*=(value_type v) GSL_NOEXCEPT
+    constexpr multi_span_index& operator*=(value_type v) GSL_NOEXCEPT
     {
         std::transform(elems, elems + rank, elems,
                        [v](value_type x) { return std::multiplies<value_type>{}(x, v); });
         return *this;
     }
 
-    constexpr index& operator/=(value_type v) GSL_NOEXCEPT
+    constexpr multi_span_index& operator/=(value_type v) GSL_NOEXCEPT
     {
         std::transform(elems, elems + rank, elems,
                        [v](value_type x) { return std::divides<value_type>{}(x, v); });
@@ -497,8 +497,8 @@ namespace details
     }
 
     template <std::size_t Rank, bool Enabled = (Rank > 1),
-              typename Ret = std::enable_if_t<Enabled, index<Rank - 1>>>
-    constexpr Ret shift_left(const index<Rank>& other) GSL_NOEXCEPT
+              typename Ret = std::enable_if_t<Enabled, multi_span_index<Rank - 1>>>
+    constexpr Ret shift_left(const multi_span_index<Rank>& other) GSL_NOEXCEPT
     {
         Ret ret{};
         for (std::size_t i = 0; i < Rank - 1; ++i) {
@@ -535,7 +535,7 @@ public:
     static const std::ptrdiff_t static_size = MyRanges::TotalSize;
 
     using size_type = std::ptrdiff_t;
-    using index_type = index<rank>;
+    using index_type = multi_span_index<rank>;
     using const_index_type = std::add_const_t<index_type>;
     using iterator = bounds_iterator<const_index_type>;
     using const_iterator = bounds_iterator<const_index_type>;
@@ -631,9 +631,9 @@ public:
         return m_ranges.contains(idx) != -1;
     }
 
-    constexpr size_type operator[](std::size_t index) const GSL_NOEXCEPT
+    constexpr size_type operator[](std::size_t idx) const GSL_NOEXCEPT
     {
-        return m_ranges.elementNum(index);
+        return m_ranges.elementNum(idx);
     }
 
     template <std::size_t Dim = 0>
@@ -698,7 +698,7 @@ public:
     using const_reference = std::add_const_t<reference>;
     using size_type = value_type;
     using difference_type = value_type;
-    using index_type = index<rank>;
+    using index_type = multi_span_index<rank>;
     using const_index_type = std::add_const_t<index_type>;
     using iterator = bounds_iterator<const_index_type>;
     using const_iterator = bounds_iterator<const_index_type>;
@@ -1478,15 +1478,15 @@ public:
     constexpr pointer data() const GSL_NOEXCEPT { return data_; }
 
     template <typename FirstIndex>
-    constexpr reference operator()(FirstIndex index)
+    constexpr reference operator()(FirstIndex idx)
     {
-        return this->operator[](narrow_cast<std::ptrdiff_t>(index));
+        return this->operator[](narrow_cast<std::ptrdiff_t>(idx));
     }
 
     template <typename FirstIndex, typename... OtherIndices>
-    constexpr reference operator()(FirstIndex index, OtherIndices... indices)
+    constexpr reference operator()(FirstIndex firstIndex, OtherIndices... indices)
     {
-        index_type idx = {narrow_cast<std::ptrdiff_t>(index),
+        index_type idx = {narrow_cast<std::ptrdiff_t>(firstIndex),
                           narrow_cast<std::ptrdiff_t>(indices)...};
         return this->operator[](idx);
     }
diff --git a/include/gsl/span b/include/gsl/span
index 6f87633..9d67fb6 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -125,10 +125,10 @@ namespace details
 
         span_iterator() = default;
 
-        constexpr span_iterator(const Span* span, typename Span::index_type index) GSL_NOEXCEPT
-            : span_(span), index_(index)
+        constexpr span_iterator(const Span* span, typename Span::index_type idx) GSL_NOEXCEPT
+            : span_(span), index_(idx)
         {
-            Expects(span == nullptr || (0 <= index_ && index <= span_->size()));
+            Expects(span == nullptr || (0 <= index_ && index_ <= span_->size()));
         }
 
         friend span_iterator<Span, true>;
@@ -662,10 +662,10 @@ span<typename Ptr::element_type> make_span(Ptr& cont)
 
 // Specialization of gsl::at for span
 template <class ElementType, std::ptrdiff_t Extent>
-constexpr ElementType& at(span<ElementType, Extent> s, std::ptrdiff_t index)
+constexpr ElementType& at(span<ElementType, Extent> s, index i)
 {
     // No bounds checking here because it is done in span::operator[] called below
-    return s[index];
+    return s[i];
 }
 
 } // namespace gsl
diff --git a/tests/multi_span_tests.cpp b/tests/multi_span_tests.cpp
index 52df759..549dcbe 100644
--- a/tests/multi_span_tests.cpp
+++ b/tests/multi_span_tests.cpp
@@ -1243,7 +1243,7 @@ TEST_CASE("empty_spans")
     {
         multi_span<int, 0> empty_av(nullptr);
 
-        CHECK(empty_av.bounds().index_bounds() == index<1>{0});
+        CHECK(empty_av.bounds().index_bounds() == multi_span_index<1>{0});
         CHECK_THROWS_AS(empty_av[0], fail_fast);
         CHECK_THROWS_AS(empty_av.begin()[0], fail_fast);
         CHECK_THROWS_AS(empty_av.cbegin()[0], fail_fast);
@@ -1255,7 +1255,7 @@ TEST_CASE("empty_spans")
 
     {
         multi_span<int> empty_av = {};
-        CHECK(empty_av.bounds().index_bounds() == index<1>{0});
+        CHECK(empty_av.bounds().index_bounds() == multi_span_index<1>{0});
         CHECK_THROWS_AS(empty_av[0], fail_fast);
         CHECK_THROWS_AS(empty_av.begin()[0], fail_fast);
         CHECK_THROWS_AS(empty_av.cbegin()[0], fail_fast);
@@ -1277,13 +1277,13 @@ TEST_CASE("index_constructor")
     multi_span<int, dynamic_range> av(arr, 8);
 
     ptrdiff_t a[1] = {0};
-    index<1> i = a;
+    multi_span_index<1> i = a;
 
     CHECK(av[i] == 4);
 
     auto av2 = as_multi_span(av, dim<4>(), dim(2));
     ptrdiff_t a2[2] = {0, 1};
-    index<2> i2 = a2;
+    multi_span_index<2> i2 = a2;
 
     CHECK(av2[i2] == 0);
     CHECK(av2[0][i] == 4);
@@ -1295,70 +1295,70 @@ TEST_CASE("index_constructors")
 {
     {
         // components of the same type
-        index<3> i1(0, 1, 2);
+        multi_span_index<3> i1(0, 1, 2);
         CHECK(i1[0] == 0);
 
         // components of different types
         std::size_t c0 = 0;
         std::size_t c1 = 1;
-        index<3> i2(c0, c1, 2);
+        multi_span_index<3> i2(c0, c1, 2);
         CHECK(i2[0] == 0);
 
         // from array
-        index<3> i3 = {0, 1, 2};
+        multi_span_index<3> i3 = {0, 1, 2};
         CHECK(i3[0] == 0);
 
         // from other index of the same size type
-        index<3> i4 = i3;
+        multi_span_index<3> i4 = i3;
         CHECK(i4[0] == 0);
 
         // default
-        index<3> i7;
+        multi_span_index<3> i7;
         CHECK(i7[0] == 0);
 
         // default
-        index<3> i9 = {};
+        multi_span_index<3> i9 = {};
         CHECK(i9[0] == 0);
     }
 
     {
         // components of the same type
-        index<1> i1(0);
+        multi_span_index<1> i1(0);
         CHECK(i1[0] == 0);
 
         // components of different types
         std::size_t c0 = 0;
-        index<1> i2(c0);
+        multi_span_index<1> i2(c0);
         CHECK(i2[0] == 0);
 
         // from array
-        index<1> i3 = {0};
+        multi_span_index<1> i3 = {0};
         CHECK(i3[0] == 0);
 
         // from int
-        index<1> i4 = 0;
+        multi_span_index<1> i4 = 0;
         CHECK(i4[0] == 0);
 
         // from other index of the same size type
-        index<1> i5 = i3;
+        multi_span_index<1> i5 = i3;
         CHECK(i5[0] == 0);
 
         // default
-        index<1> i8;
+        multi_span_index<1> i8;
         CHECK(i8[0] == 0);
 
         // default
-        index<1> i9 = {};
+        multi_span_index<1> i9 = {};
         CHECK(i9[0] == 0);
     }
 
     #ifdef CONFIRM_COMPILATION_ERRORS
     {
-    index<3> i1(0, 1);
-    index<3> i2(0, 1, 2, 3);
-    index<3> i3 = {0};
-    index<3> i4 = {0, 1, 2, 3};
-    index<1> i5 = {0, 1};
+    multi_span_index<3> i1(0, 1);
+    multi_span_index<3> i2(0, 1, 2, 3);
+    multi_span_index<3> i3 = {0};
+    multi_span_index<3> i4 = {0, 1, 2, 3};
+    multi_span_index<1> i5 = {0, 1};
     }
     #endif
 }
@@ -1367,15 +1367,15 @@ TEST_CASE("index_operations")
 {
     ptrdiff_t a[3] = {0, 1, 2};
     ptrdiff_t b[3] = {3, 4, 5};
-    index<3> i = a;
-    index<3> j = b;
+    multi_span_index<3> i = a;
+    multi_span_index<3> j = b;
 
     CHECK(i[0] == 0);
     CHECK(i[1] == 1);
     CHECK(i[2] == 2);
 
     {
-        index<3> k = i + j;
+        multi_span_index<3> k = i + j;
 
         CHECK(i[0] == 0);
         CHECK(i[1] == 1);
@@ -1386,7 +1386,7 @@ TEST_CASE("index_operations")
     }
 
     {
-        index<3> k = i * 3;
+        multi_span_index<3> k = i * 3;
 
         CHECK(i[0] == 0);
         CHECK(i[1] == 1);
@@ -1397,7 +1397,7 @@ TEST_CASE("index_operations")
     }
 
     {
-        index<3> k = 3 * i;
+        multi_span_index<3> k = 3 * i;
 
         CHECK(i[0] == 0);
         CHECK(i[1] == 1);
@@ -1408,7 +1408,7 @@ TEST_CASE("index_operations")
     }
 
     {
-        index<2> k = details::shift_left(i);
+        multi_span_index<2> k = details::shift_left(i);
 
         CHECK(i[0] == 0);
         CHECK(i[1] == 1);
@@ -1431,7 +1431,7 @@ void iterate_second_column(multi_span<int, dynamic_range, dynamic_range> av)
     }
 
     for (auto i = 0; i < section.size(); ++i) {
-        auto idx = index<2>{i, 0}; // avoid braces inside the CHECK macro
+        auto idx = multi_span_index<2>{i, 0}; // avoid braces inside the CHECK macro
         CHECK(section[idx] == av[i][1]);
     }
 
@@ -1439,7 +1439,7 @@ void iterate_second_column(multi_span<int, dynamic_range, dynamic_range> av)
     CHECK(section.bounds().index_bounds()[1] == 1);
     for (auto i = 0; i < section.bounds().index_bounds()[0]; ++i) {
         for (auto j = 0; j < section.bounds().index_bounds()[1]; ++j) {
-            auto idx = index<2>{i, j}; // avoid braces inside the CHECK macro
+            auto idx = multi_span_index<2>{i, j}; // avoid braces inside the CHECK macro
             CHECK(section[idx] == av[i][1]);
         }
     }
diff --git a/tests/strided_span_tests.cpp b/tests/strided_span_tests.cpp
index 2c1c047..8719336 100644
--- a/tests/strided_span_tests.cpp
+++ b/tests/strided_span_tests.cpp
@@ -48,8 +48,8 @@ TEST_CASE("span_section_test")
     int a[30][4][5];
 
     const auto av = as_multi_span(a);
-    const auto sub = av.section({15, 0, 0}, gsl::index<3>{2, 2, 2});
-    const auto subsub = sub.section({1, 0, 0}, gsl::index<3>{1, 1, 1});
+    const auto sub = av.section({15, 0, 0}, gsl::multi_span_index<3>{2, 2, 2});
+    const auto subsub = sub.section({1, 0, 0}, gsl::multi_span_index<3>{1, 1, 1});
     (void) subsub;
 }
 
@@ -79,18 +79,18 @@ TEST_CASE("strided_span_constructors")
         const int carr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
 
         strided_span<int, 1> sav1{arr, {{9}, {1}}}; // T -> T
-        CHECK(sav1.bounds().index_bounds() == index<1>{9});
+        CHECK(sav1.bounds().index_bounds() == multi_span_index<1>{9});
         CHECK(sav1.bounds().stride() == 1);
         CHECK((sav1[0] == 1 && sav1[8] == 9));
 
         strided_span<const int, 1> sav2{carr, {{4}, {2}}}; // const T -> const T
-        CHECK(sav2.bounds().index_bounds() == index<1>{4});
-        CHECK(sav2.bounds().strides() == index<1>{2});
+        CHECK(sav2.bounds().index_bounds() == multi_span_index<1>{4});
+        CHECK(sav2.bounds().strides() == multi_span_index<1>{2});
         CHECK((sav2[0] == 1 && sav2[3] == 7));
 
         strided_span<int, 2> sav3{arr, {{2, 2}, {6, 2}}}; // T -> const T
-        CHECK((sav3.bounds().index_bounds() == index<2>{2, 2}));
-        CHECK((sav3.bounds().strides() == index<2>{6, 2}));
+        CHECK((sav3.bounds().index_bounds() == multi_span_index<2>{2, 2}));
+        CHECK((sav3.bounds().strides() == multi_span_index<2>{6, 2}));
         CHECK((sav3[{0, 0}] == 1 && sav3[{0, 1}] == 3 && sav3[{1, 0}] == 7));
     }
 
@@ -103,8 +103,8 @@ TEST_CASE("strided_span_constructors")
             const multi_span<int> src = arr;
 
             strided_span<int, 1> sav{src, {2, 1}};
-            CHECK(sav.bounds().index_bounds() == index<1>{2});
-            CHECK(sav.bounds().strides() == index<1>{1});
+            CHECK(sav.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav[1] == 2);
 
 #if _MSC_VER > 1800
@@ -115,8 +115,8 @@ TEST_CASE("strided_span_constructors")
             strided_span<const int, 1> sav_c{multi_span<const int>{src},
                                              strided_bounds<1>{2, 1}};
 #endif
-            CHECK(sav_c.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_c.bounds().strides() == index<1>{1});
+            CHECK(sav_c.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_c.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_c[1] == 2);
 
 #if _MSC_VER > 1800
@@ -125,8 +125,8 @@ TEST_CASE("strided_span_constructors")
             strided_span<volatile int, 1> sav_v{multi_span<volatile int>{src},
                                                 strided_bounds<1>{2, 1}};
 #endif
-            CHECK(sav_v.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_v.bounds().strides() == index<1>{1});
+            CHECK(sav_v.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_v.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_v[1] == 2);
 
 #if _MSC_VER > 1800
@@ -135,8 +135,8 @@ TEST_CASE("strided_span_constructors")
             strided_span<const volatile int, 1> sav_cv{multi_span<const volatile int>{src},
                                                        strided_bounds<1>{2, 1}};
 #endif
-            CHECK(sav_cv.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_cv.bounds().strides() == index<1>{1});
+            CHECK(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_cv.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_cv[1] == 2);
         }
 
@@ -145,8 +145,8 @@ TEST_CASE("strided_span_constructors")
             const multi_span<const int> src{arr};
 
             strided_span<const int, 1> sav_c{src, {2, 1}};
-            CHECK(sav_c.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_c.bounds().strides() == index<1>{1});
+            CHECK(sav_c.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_c.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_c[1] == 2);
 
 #if _MSC_VER > 1800
@@ -156,8 +156,8 @@ TEST_CASE("strided_span_constructors")
                                                        strided_bounds<1>{2, 1}};
 #endif
 
-            CHECK(sav_cv.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_cv.bounds().strides() == index<1>{1});
+            CHECK(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_cv.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_cv[1] == 2);
         }
 
@@ -166,8 +166,8 @@ TEST_CASE("strided_span_constructors")
             const multi_span<volatile int> src{arr};
 
             strided_span<volatile int, 1> sav_v{src, {2, 1}};
-            CHECK(sav_v.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_v.bounds().strides() == index<1>{1});
+            CHECK(sav_v.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_v.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_v[1] == 2);
 
 #if _MSC_VER > 1800
@@ -176,8 +176,8 @@ TEST_CASE("strided_span_constructors")
             strided_span<const volatile int, 1> sav_cv{multi_span<const volatile int>{src},
                                                        strided_bounds<1>{2, 1}};
 #endif
-            CHECK(sav_cv.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_cv.bounds().strides() == index<1>{1});
+            CHECK(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_cv.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_cv[1] == 2);
         }
 
@@ -186,8 +186,8 @@ TEST_CASE("strided_span_constructors")
             const multi_span<const volatile int> src{arr};
 
             strided_span<const volatile int, 1> sav_cv{src, {2, 1}};
-            CHECK(sav_cv.bounds().index_bounds() == index<1>{2});
-            CHECK(sav_cv.bounds().strides() == index<1>{1});
+            CHECK(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            CHECK(sav_cv.bounds().strides() == multi_span_index<1>{1});
             CHECK(sav_cv[1] == 2);
         }
     }
@@ -206,7 +206,7 @@ TEST_CASE("strided_span_constructors")
 
         const strided_span<int, 1> src{arr, {2, 1}};
         strided_span<const int, 1> sav{src};
-        CHECK(sav.bounds().index_bounds() == index<1>{2});
+        CHECK(sav.bounds().index_bounds() == multi_span_index<1>{2});
         CHECK(sav.bounds().stride() == 1);
         CHECK(sav[1] == 5);
 
@@ -221,15 +221,15 @@ TEST_CASE("strided_span_constructors")
         const strided_span<int, 1> src1{arr1, {2, 1}};
         strided_span<int, 1> sav1{src1};
 
-        CHECK(sav1.bounds().index_bounds() == index<1>{2});
+        CHECK(sav1.bounds().index_bounds() == multi_span_index<1>{2});
         CHECK(sav1.bounds().stride() == 1);
         CHECK(sav1[0] == 3);
 
         int arr2[6] = {1, 2, 3, 4, 5, 6};
         const strided_span<const int, 2> src2{arr2, {{3, 2}, {2, 1}}};
         strided_span<const int, 2> sav2{src2};
-        CHECK((sav2.bounds().index_bounds() == index<2>{3, 2}));
-        CHECK((sav2.bounds().strides() == index<2>{2, 1}));
+        CHECK((sav2.bounds().index_bounds() == multi_span_index<2>{3, 2}));
+        CHECK((sav2.bounds().strides() == multi_span_index<2>{2, 1}));
         CHECK((sav2[{0, 0}] == 1 && sav2[{2, 0}] == 5));
     }
 
@@ -241,8 +241,8 @@ TEST_CASE("strided_span_constructors")
         const strided_span<int, 1> src{arr1, {{2}, {1}}};
         strided_span<const int, 1> sav{arr2, {{3}, {2}}};
         strided_span<const int, 1>& sav_ref = (sav = src);
-        CHECK(sav.bounds().index_bounds() == index<1>{2});
-        CHECK(sav.bounds().strides() == index<1>{1});
+        CHECK(sav.bounds().index_bounds() == multi_span_index<1>{2});
+        CHECK(sav.bounds().strides() == multi_span_index<1>{1});
         CHECK(sav[0] == 1);
         CHECK(&sav_ref == &sav);
     }
@@ -254,8 +254,8 @@ TEST_CASE("strided_span_constructors")
         const strided_span<int, 1> src1{arr1, {2, 1}};
         strided_span<int, 1> sav1{arr1b, {1, 1}};
         strided_span<int, 1>& sav1_ref = (sav1 = src1);
-        CHECK(sav1.bounds().index_bounds() == index<1>{2});
-        CHECK(sav1.bounds().strides() == index<1>{1});
+        CHECK(sav1.bounds().index_bounds() == multi_span_index<1>{2});
+        CHECK(sav1.bounds().strides() == multi_span_index<1>{1});
         CHECK(sav1[0] == 3);
         CHECK(&sav1_ref == &sav1);
 
@@ -264,8 +264,8 @@ TEST_CASE("strided_span_constructors")
         const strided_span<const int, 2> src2{arr2, {{3, 2}, {2, 1}}};
         strided_span<const int, 2> sav2{arr2b, {{1, 1}, {1, 1}}};
         strided_span<const int, 2>& sav2_ref = (sav2 = src2);
-        CHECK((sav2.bounds().index_bounds() == index<2>{3, 2}));
-        CHECK((sav2.bounds().strides() == index<2>{2, 1}));
+        CHECK((sav2.bounds().index_bounds() == multi_span_index<2>{3, 2}));
+        CHECK((sav2.bounds().strides() == multi_span_index<2>{2, 1}));
         CHECK((sav2[{0, 0}] == 1 && sav2[{2, 0}] == 5));
         CHECK(&sav2_ref == &sav2);
     }
@@ -322,7 +322,7 @@ TEST_CASE("strided_span_column_major")
     // Section
     strided_span<int, 2> cm_sec = cm_sav.section({2, 1}, {3, 2});
 
-    CHECK((cm_sec.bounds().index_bounds() == index<2>{3, 2}));
+    CHECK((cm_sec.bounds().index_bounds() == multi_span_index<2>{3, 2}));
     CHECK((cm_sec[{0, 0}] == 8));
     CHECK((cm_sec[{0, 1}] == 9));
     CHECK((cm_sec[{1, 0}] == 11));
@@ -371,7 +371,7 @@ TEST_CASE("strided_span_bounds")
     {
         // strided array ctor with matching strided bounds
         strided_span<int, 1> sav{arr, {4, 1}};
-        CHECK(sav.bounds().index_bounds() == index<1>{4});
+        CHECK(sav.bounds().index_bounds() == multi_span_index<1>{4});
         CHECK(sav[3] == 3);
         CHECK_THROWS_AS(sav[4], fail_fast);
     }
@@ -379,7 +379,7 @@ TEST_CASE("strided_span_bounds")
     {
         // strided array ctor with smaller strided bounds
         strided_span<int, 1> sav{arr, {2, 1}};
-        CHECK(sav.bounds().index_bounds() == index<1>{2});
+        CHECK(sav.bounds().index_bounds() == multi_span_index<1>{2});
         CHECK(sav[1] == 1);
         CHECK_THROWS_AS(sav[2], fail_fast);
     }
@@ -387,7 +387,7 @@ TEST_CASE("strided_span_bounds")
     {
         // strided array ctor with fitting irregular bounds
         strided_span<int, 1> sav{arr, {2, 3}};
-        CHECK(sav.bounds().index_bounds() == index<1>{2});
+        CHECK(sav.bounds().index_bounds() == multi_span_index<1>{2});
         CHECK(sav[0] == 0);
         CHECK(sav[1] == 3);
         CHECK_THROWS_AS(sav[2], fail_fast);
@@ -433,7 +433,7 @@ TEST_CASE("strided_span_bounds")
         strided_span<int, 2> sav7{av.as_multi_span(dim<2>(), dim<2>()),
                                   {{1, 1}, {1, 1}, {1, 1}}};
 
-        index<1> index{0, 1};
+        multi_span_index<1> index{0, 1};
         strided_span<int, 1> sav8{arr, {1, {1, 1}}};
         strided_span<int, 1> sav9{arr, {{1, 1}, {1, 1}}};
         strided_span<int, 1> sav10{av, {1, {1, 1}}};
@@ -548,7 +548,7 @@ TEST_CASE("empty_strided_spans")
         multi_span<int, 0> empty_av(nullptr);
         strided_span<int, 1> empty_sav{empty_av, {0, 1}};
 
-        CHECK(empty_sav.bounds().index_bounds() == index<1>{0});
+        CHECK(empty_sav.bounds().index_bounds() == multi_span_index<1>{0});
         CHECK_THROWS_AS(empty_sav[0], fail_fast);
         CHECK_THROWS_AS(empty_sav.begin()[0], fail_fast);
         CHECK_THROWS_AS(empty_sav.cbegin()[0], fail_fast);
@@ -562,7 +562,7 @@ TEST_CASE("empty_strided_spans")
     {
         strided_span<int, 1> empty_sav{nullptr, 0, {0, 1}};
 
-        CHECK(empty_sav.bounds().index_bounds() == index<1>{0});
+        CHECK(empty_sav.bounds().index_bounds() == multi_span_index<1>{0});
         CHECK_THROWS_AS(empty_sav[0], fail_fast);
         CHECK_THROWS_AS(empty_sav.begin()[0], fail_fast);
         CHECK_THROWS_AS(empty_sav.cbegin()[0], fail_fast);
@@ -582,7 +582,7 @@ void iterate_every_other_element(multi_span<int, dynamic_range> av)
 #if _MSC_VER > 1800
     auto bounds = strided_bounds<1>({length}, {2});
 #else
-    auto bounds = strided_bounds<1>(index<1>{length}, index<1>{2});
+    auto bounds = strided_bounds<1>(multi_span_index<1>{length}, multi_span_index<1>{2});
 #endif
     strided_span<int, 1> strided(&av.data()[1], av.size() - 1, bounds);
 
@@ -638,7 +638,7 @@ void iterate_second_slice(multi_span<int, dynamic_range, dynamic_range, dynamic_
     for (auto i = 0; i < section.extent<0>(); ++i) {
         for (auto j = 0; j < section.extent<1>(); ++j)
             for (auto k = 0; k < section.extent<2>(); ++k) {
-                auto idx = index<3>{i, j, k}; // avoid braces in the CHECK macro
+                auto idx = multi_span_index<3>{i, j, k}; // avoid braces in the CHECK macro
                 CHECK(section[idx] == expected[2 * i + 2 * j + k]);
             }
     }
diff --git a/tests/utils_tests.cpp b/tests/utils_tests.cpp
index 610efbf..587b0a1 100644
--- a/tests/utils_tests.cpp
+++ b/tests/utils_tests.cpp
@@ -18,13 +18,20 @@
 
 #include <gsl/gsl_util> // for narrow, finally, narrow_cast, narrowing_e...
 
-#include <algorithm>  // for move
-#include <functional> // for reference_wrapper, _Bind_helper<>::type
-#include <limits>     // for numeric_limits
-#include <stdint.h>   // for uint32_t, int32_t
+#include <algorithm>   // for move
+#include <functional>  // for reference_wrapper, _Bind_helper<>::type
+#include <limits>      // for numeric_limits
+#include <stdint.h>    // for uint32_t, int32_t
+#include <type_traits> // for is_same
 
 using namespace gsl;
 
+TEST_CASE("sanity check for gsl::index typedef")
+{
+    static_assert(std::is_same<gsl::index, std::ptrdiff_t>::value,
+                  "gsl::index represents wrong arithmetic type");
+}
+
 void f(int& i) { i += 1; }
 
 TEST_CASE("finally_lambda")