From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Fri, 19 Apr 2024 02:47:55 +0200
Subject: Adding upstream version 124.0.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 mfbt/tests/gtest/TestSpan.cpp | 2355 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 2355 insertions(+)
 create mode 100644 mfbt/tests/gtest/TestSpan.cpp

(limited to 'mfbt/tests/gtest/TestSpan.cpp')

diff --git a/mfbt/tests/gtest/TestSpan.cpp b/mfbt/tests/gtest/TestSpan.cpp
new file mode 100644
index 0000000000..fb7db0d158
--- /dev/null
+++ b/mfbt/tests/gtest/TestSpan.cpp
@@ -0,0 +1,2355 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+// Adapted from
+// https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/tests/Span_tests.cpp
+
+#include "gtest/gtest.h"
+
+#include "mozilla/Array.h"
+#include "mozilla/Span.h"
+
+#include "nsString.h"
+#include "nsTArray.h"
+#include "mozilla/Range.h"
+
+#include <type_traits>
+
+#define SPAN_TEST(name) TEST(SpanTest, name)
+#define CHECK_THROW(a, b)
+
+using namespace mozilla;
+
+static_assert(std::is_convertible_v<Range<int>, Span<const int>>,
+              "Range should convert into const");
+static_assert(std::is_convertible_v<Range<const int>, Span<const int>>,
+              "const Range should convert into const");
+static_assert(!std::is_convertible_v<Range<const int>, Span<int>>,
+              "Range should not drop const in conversion");
+static_assert(std::is_convertible_v<Span<int>, Range<const int>>,
+              "Span should convert into const");
+static_assert(std::is_convertible_v<Span<const int>, Range<const int>>,
+              "const Span should convert into const");
+static_assert(!std::is_convertible_v<Span<const int>, Range<int>>,
+              "Span should not drop const in conversion");
+static_assert(std::is_convertible_v<Span<const int>, Span<const int>>,
+              "const Span should convert into const");
+static_assert(std::is_convertible_v<Span<int>, Span<const int>>,
+              "Span should convert into const");
+static_assert(!std::is_convertible_v<Span<const int>, Span<int>>,
+              "Span should not drop const in conversion");
+static_assert(std::is_convertible_v<const nsTArray<int>, Span<const int>>,
+              "const nsTArray should convert into const");
+static_assert(std::is_convertible_v<nsTArray<int>, Span<const int>>,
+              "nsTArray should convert into const");
+static_assert(!std::is_convertible_v<const nsTArray<int>, Span<int>>,
+              "nsTArray should not drop const in conversion");
+static_assert(std::is_convertible_v<nsTArray<const int>, Span<const int>>,
+              "nsTArray should convert into const");
+static_assert(!std::is_convertible_v<nsTArray<const int>, Span<int>>,
+              "nsTArray should not drop const in conversion");
+
+static_assert(std::is_convertible_v<const std::vector<int>, Span<const int>>,
+              "const std::vector should convert into const");
+static_assert(std::is_convertible_v<std::vector<int>, Span<const int>>,
+              "std::vector should convert into const");
+static_assert(!std::is_convertible_v<const std::vector<int>, Span<int>>,
+              "std::vector should not drop const in conversion");
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_CONST_INT_PTR reinterpret_cast<const int*>(alignof(const int))
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_INT_PTR reinterpret_cast<int*>(alignof(int))
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_CONST_INT_PTR_PTR \
+  reinterpret_cast<const int**>(alignof(const int*))
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_INT_PTR_PTR reinterpret_cast<int**>(alignof(int*))
+
+namespace {
+struct BaseClass {};
+struct DerivedClass : BaseClass {};
+}  // namespace
+
+void AssertSpanOfThreeInts(Span<const int> s) {
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 1);
+  ASSERT_EQ(s[1], 2);
+  ASSERT_EQ(s[2], 3);
+}
+
+void AssertSpanOfThreeChars(Span<const char> s) {
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 'a');
+  ASSERT_EQ(s[1], 'b');
+  ASSERT_EQ(s[2], 'c');
+}
+
+void AssertSpanOfThreeChar16s(Span<const char16_t> s) {
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 'a');
+  ASSERT_EQ(s[1], 'b');
+  ASSERT_EQ(s[2], 'c');
+}
+
+void AssertSpanOfThreeCharsViaString(const nsACString& aStr) {
+  AssertSpanOfThreeChars(aStr);
+}
+
+void AssertSpanOfThreeChar16sViaString(const nsAString& aStr) {
+  AssertSpanOfThreeChar16s(aStr);
+}
+
+SPAN_TEST(default_constructor) {
+  {
+    Span<int> s;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int, 0> s;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int, 0> cs;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<int, 1> s;
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);  // explains why it can't compile
+#endif
+  }
+
+  {
+    Span<int> s{};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs{};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+}
+
+SPAN_TEST(size_optimization) {
+  {
+    Span<int> s;
+    ASSERT_EQ(sizeof(s), sizeof(int*) + sizeof(size_t));
+  }
+
+  {
+    Span<int, 0> s;
+    ASSERT_EQ(sizeof(s), sizeof(int*));
+  }
+}
+
+SPAN_TEST(from_nullptr_constructor) {
+  {
+    Span<int> s = nullptr;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs = nullptr;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int, 0> s = nullptr;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int, 0> cs = nullptr;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<int, 1> s = nullptr;
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);  // explains why it can't compile
+#endif
+  }
+
+  {
+    Span<int> s{nullptr};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs{nullptr};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int*> s{nullptr};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR_PTR);
+
+    Span<const int*> cs{nullptr};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR_PTR);
+  }
+}
+
+SPAN_TEST(from_nullptr_length_constructor) {
+  {
+    Span<int> s{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int, 0> s{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int, 0> cs{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+#if 0
+        {
+            auto workaround_macro = []() { Span<int, 1> s{ nullptr, static_cast<Span<int>::index_type>(0) }; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { Span<int> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { Span<const int> cs{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { Span<int, 0> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { Span<const int, 0> s{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+#endif
+  {
+    Span<int*> s{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR_PTR);
+
+    Span<const int*> cs{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR_PTR);
+  }
+}
+
+SPAN_TEST(from_pointer_length_constructor) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s{&arr[0], 2};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int, 2> s{&arr[0], 2};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    int* p = nullptr;
+    Span<int> s{p, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+#if 0
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { Span<int> s{p, 2}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+#endif
+
+  {
+    auto s = Span(&arr[0], 2);
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    int* p = nullptr;
+    auto s = Span(p, static_cast<Span<int>::index_type>(0));
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+#if 0
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { Span(p, 2); };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+#endif
+}
+
+SPAN_TEST(from_pointer_pointer_constructor) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s{&arr[0], &arr[2]};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int, 2> s{&arr[0], &arr[2]};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int> s{&arr[0], &arr[0]};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 0> s{&arr[0], &arr[0]};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  // this will fail the std::distance() precondition, which asserts on MSVC
+  // debug builds
+  //{
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[1], &arr[0]}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  // this will fail the std::distance() precondition, which asserts on MSVC
+  // debug builds
+  //{
+  //    int* p = nullptr;
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[0], p}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  {
+    int* p = nullptr;
+    Span<int> s{p, p};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+  {
+    int* p = nullptr;
+    Span<int, 0> s{p, p};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+  // this will fail the std::distance() precondition, which asserts on MSVC
+  // debug builds
+  //{
+  //    int* p = nullptr;
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[0], p}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  {
+    auto s = Span(&arr[0], &arr[2]);
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    auto s = Span(&arr[0], &arr[0]);
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    int* p = nullptr;
+    auto s = Span(p, p);
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+}
+
+SPAN_TEST(from_array_constructor) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int> s{arr};
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 5> s{arr};
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  int arr2d[2][3] = {{1, 2, 3}, {4, 5, 6}};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  { Span<int, 6> s{arr}; }
+
+  {
+    Span<int, 0> s{arr};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int> s{arr2d};
+    ASSERT_EQ(s.Length(), 6U);
+    ASSERT_EQ(s.data(), &arr2d[0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[5], 6);
+  }
+
+  {
+    Span<int, 0> s{arr2d};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr2d[0][0]);
+  }
+
+  { Span<int, 6> s{arr2d}; }
+#endif
+  {
+    Span<int[3]> s{&(arr2d[0]), 1};
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr2d[0]);
+  }
+
+  int arr3d[2][3][2] = {{{1, 2}, {3, 4}, {5, 6}}, {{7, 8}, {9, 10}, {11, 12}}};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int> s{arr3d};
+    ASSERT_EQ(s.Length(), 12U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[11], 12);
+  }
+
+  {
+    Span<int, 0> s{arr3d};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+  }
+
+  { Span<int, 11> s{arr3d}; }
+
+  {
+    Span<int, 12> s{arr3d};
+    ASSERT_EQ(s.Length(), 12U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[5], 6);
+  }
+#endif
+  {
+    Span<int[3][2]> s{&arr3d[0], 1};
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr3d[0]);
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    auto s = Span(&(arr2d[0]), 1);
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr2d[0]);
+  }
+
+  {
+    auto s = Span(&arr3d[0], 1);
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr3d[0]);
+  }
+}
+
+SPAN_TEST(from_dynamic_array_constructor) {
+  double(*arr)[3][4] = new double[100][3][4];
+
+  {
+    Span<double> s(&arr[0][0][0], 10);
+    ASSERT_EQ(s.Length(), 10U);
+    ASSERT_EQ(s.data(), &arr[0][0][0]);
+  }
+
+  {
+    auto s = Span(&arr[0][0][0], 10);
+    ASSERT_EQ(s.Length(), 10U);
+    ASSERT_EQ(s.data(), &arr[0][0][0]);
+  }
+
+  delete[] arr;
+}
+
+SPAN_TEST(from_std_array_constructor) {
+  std::array<int, 4> arr = {{1, 2, 3, 4}};
+
+  {
+    Span<int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  {
+    Span<int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 4> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 2> cs{arr};
+    ASSERT_EQ(cs.size(), 2U);
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  {
+    Span<int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 0> cs{arr};
+    ASSERT_EQ(cs.size(), 0U);
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  { Span<int, 5> s{arr}; }
+
+  {
+    auto get_an_array = []() -> std::array<int, 4> { return {1, 2, 3, 4}; };
+    auto take_a_Span = [](Span<int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto get_an_array = []() -> std::array<int, 4> { return {{1, 2, 3, 4}}; };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_const_std_array_constructor) {
+  const std::array<int, 4> arr = {{1, 2, 3, 4}};
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  { Span<const int, 5> s{arr}; }
+#endif
+
+  {
+    auto get_an_array = []() -> const std::array<int, 4> {
+      return {{1, 2, 3, 4}};
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_std_array_const_constructor) {
+  std::array<const int, 4> arr = {{1, 2, 3, 4}};
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  { Span<const int, 5> s{arr}; }
+
+  { Span<int, 4> s{arr}; }
+#endif
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_mozilla_array_constructor) {
+  mozilla::Array<int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 4> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 2> cs{arr};
+    ASSERT_EQ(cs.size(), 2U);
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 0> cs{arr};
+    ASSERT_EQ(cs.size(), 0U);
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  { Span<int, 5> s{arr}; }
+
+  {
+    auto get_an_array = []() -> mozilla::Array<int, 4> { return {1, 2, 3, 4}; };
+    auto take_a_Span = [](Span<int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto get_an_array = []() -> mozilla::Array<int, 4> { return {1, 2, 3, 4}; };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_const_mozilla_array_constructor) {
+  const mozilla::Array<int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  { Span<const int, 5> s{arr}; }
+#endif
+
+#if 0
+  {
+    auto get_an_array = []() -> const mozilla::Array<int, 4> {
+      return { 1, 2, 3, 4 };
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_mozilla_array_const_constructor) {
+  mozilla::Array<const int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  { Span<const int, 5> s{arr}; }
+
+  { Span<int, 4> s{arr}; }
+#endif
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_container_constructor) {
+  std::vector<int> v = {1, 2, 3};
+  const std::vector<int> cv = v;
+
+  {
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(s.data(), v.data());
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(cs.data(), v.data());
+  }
+
+  std::string str = "hello";
+  const std::string cstr = "hello";
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> s{str};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.size()));
+    ASSERT_EQ(s.data(), str.data());
+#endif
+    Span<const char> cs{str};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.size()));
+    ASSERT_EQ(cs.data(), str.data());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> s{cstr};
+#endif
+    Span<const char> cs{cstr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(cstr.size()));
+    ASSERT_EQ(cs.data(), cstr.data());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_vector = []() -> std::vector<int> { return {}; };
+    auto use_Span = [](Span<int> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+#endif
+  }
+
+  {
+    auto get_temp_vector = []() -> std::vector<int> { return {}; };
+    auto use_Span = [](Span<const int> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_string = []() -> std::string { return {}; };
+    auto use_Span = [](Span<char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+#endif
+  }
+
+  {
+    auto get_temp_string = []() -> std::string { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_vector = []() -> const std::vector<int> { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+#endif
+  }
+
+  {
+    auto get_temp_string = []() -> const std::string { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    std::map<int, int> m;
+    Span<int> s{m};
+#endif
+  }
+
+  {
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(s.data(), v.data());
+
+    auto cs = Span(cv);
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(cv.size()));
+    ASSERT_EQ(cs.data(), cv.data());
+  }
+}
+
+SPAN_TEST(from_xpcom_collections) {
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    AutoTArray<int, 5> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    AutoTArray<int, 5> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    FallibleTArray<int> v;
+    *(v.AppendElement(fallible)) = 1;
+    *(v.AppendElement(fallible)) = 2;
+    *(v.AppendElement(fallible)) = 3;
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    FallibleTArray<int> v;
+    *(v.AppendElement(fallible)) = 1;
+    *(v.AppendElement(fallible)) = 2;
+    *(v.AppendElement(fallible)) = 3;
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    nsAutoString str;
+    str.AssignLiteral(u"abc");
+
+    AssertSpanOfThreeChar16s(str);
+    AssertSpanOfThreeChar16sViaString(str);
+
+    Span<char16_t> s{str.GetMutableData()};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginWriting());
+    ASSERT_EQ(s[2], 'c');
+
+    Span<const char16_t> cs{str};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(cs.data(), str.BeginReading());
+    ASSERT_EQ(cs[2], 'c');
+  }
+  {
+    nsAutoString str;
+    str.AssignLiteral(u"abc");
+
+    AssertSpanOfThreeChar16s(str);
+    AssertSpanOfThreeChar16sViaString(str);
+
+    auto s = Span(str);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginReading());
+    ASSERT_EQ(s[2], 'c');
+  }
+  {
+    nsAutoCString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChars(str);
+    AssertSpanOfThreeCharsViaString(str);
+
+    Span<const uint8_t> cs{str};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(cs.data(), reinterpret_cast<const uint8_t*>(str.BeginReading()));
+    ASSERT_EQ(cs[2], 'c');
+  }
+  {
+    nsAutoCString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChars(str);
+    AssertSpanOfThreeCharsViaString(str);
+
+    auto s = Span(str);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginReading());
+    ASSERT_EQ(s[2], 'c');
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    Range<int> r(v.Elements(), v.Length());
+
+    AssertSpanOfThreeInts(r);
+
+    Span<int> s{r};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{r};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    Range<int> r(v.Elements(), v.Length());
+
+    AssertSpanOfThreeInts(r);
+
+    auto s = Span(r);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+}
+
+SPAN_TEST(from_cstring) {
+  {
+    const char* str = nullptr;
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 0U);
+  }
+  {
+    const char* str = "abc";
+
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+
+    static_assert(MakeStringSpan("abc").size() == 3U);
+    static_assert(MakeStringSpan("abc")[2] == 'c');
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<const char> scccl("literal");  // error
+
+    Span<const char> sccel;
+    sccel = "literal";  // error
+
+    cs = Span("literal");  // error
+#endif
+  }
+  {
+    char arr[4] = {'a', 'b', 'c', 0};
+
+    auto cs = MakeStringSpan(arr);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), arr);
+    ASSERT_EQ(cs[2], 'c');
+
+    cs = Span(arr);
+    ASSERT_EQ(cs.size(), 4U);  // zero terminator is part of the array span.
+    ASSERT_EQ(cs.data(), arr);
+    ASSERT_EQ(cs[2], 'c');
+    ASSERT_EQ(cs[3], '\0');  // zero terminator is part of the array span.
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> scca(arr);         // error
+    Span<const char> sccca(arr);  // error
+
+    Span<const char> scccea;
+    scccea = arr;  // error
+#endif
+  }
+  {
+    const char16_t* str = nullptr;
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 0U);
+  }
+  {
+    char16_t arr[4] = {'a', 'b', 'c', 0};
+    const char16_t* str = arr;
+
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+
+    static_assert(MakeStringSpan(u"abc").size() == 3U);
+    static_assert(MakeStringSpan(u"abc")[2] == u'c');
+
+    cs = MakeStringSpan(arr);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+
+    cs = Span(arr);
+    ASSERT_EQ(cs.size(), 4U);  // zero terminator is part of the array span.
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+    ASSERT_EQ(cs[3], '\0');  // zero terminator is part of the array span.
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char16_t> scca(arr);  // error
+
+    Span<const char16_t> scccea;
+    scccea = arr;  // error
+
+    Span<const char16_t> scccl(u"literal");  // error
+
+    Span<const char16_t>* sccel;
+    *sccel = u"literal";  // error
+
+    cs = Span(u"literal");  // error
+#endif
+  }
+}
+
+SPAN_TEST(from_convertible_Span_constructor){{Span<DerivedClass> avd;
+Span<const DerivedClass> avcd = avd;
+static_cast<void>(avcd);
+}
+
+{
+#ifdef CONFIRM_COMPILATION_ERRORS
+  Span<DerivedClass> avd;
+  Span<BaseClass> avb = avd;
+  static_cast<void>(avb);
+#endif
+}
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+{
+  Span<int> s;
+  Span<unsigned int> s2 = s;
+  static_cast<void>(s2);
+}
+
+{
+  Span<int> s;
+  Span<const unsigned int> s2 = s;
+  static_cast<void>(s2);
+}
+
+{
+  Span<int> s;
+  Span<short> s2 = s;
+  static_cast<void>(s2);
+}
+#endif
+}
+
+SPAN_TEST(copy_move_and_assignment) {
+  Span<int> s1;
+  ASSERT_TRUE(s1.empty());
+
+  int arr[] = {3, 4, 5};
+
+  Span<const int> s2 = arr;
+  ASSERT_EQ(s2.Length(), 3U);
+  ASSERT_EQ(s2.data(), &arr[0]);
+
+  s2 = s1;
+  ASSERT_TRUE(s2.empty());
+
+  auto get_temp_Span = [&]() -> Span<int> { return {&arr[1], 2}; };
+  auto use_Span = [&](Span<const int> s) {
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[1]);
+  };
+  use_Span(get_temp_Span());
+
+  s1 = get_temp_Span();
+  ASSERT_EQ(s1.Length(), 2U);
+  ASSERT_EQ(s1.data(), &arr[1]);
+}
+
+SPAN_TEST(first) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<2>().Length(), 2U);
+    ASSERT_EQ(av.First(2).Length(), 2U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<0>().Length(), 0U);
+    ASSERT_EQ(av.First(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<5>().Length(), 5U);
+    ASSERT_EQ(av.First(5).Length(), 5U);
+  }
+
+#if 0
+        {
+            Span<int, 5> av = arr;
+#  ifdef CONFIRM_COMPILATION_ERRORS
+            ASSERT_EQ(av.First<6>().Length() , 6U);
+            ASSERT_EQ(av.First<-1>().Length() , -1);
+#  endif
+            CHECK_THROW(av.First(6).Length(), fail_fast);
+        }
+#endif
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.First<0>().Length(), 0U);
+    ASSERT_EQ(av.First(0).Length(), 0U);
+  }
+}
+
+SPAN_TEST(last) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<2>().Length(), 2U);
+    ASSERT_EQ(av.Last(2).Length(), 2U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<0>().Length(), 0U);
+    ASSERT_EQ(av.Last(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<5>().Length(), 5U);
+    ASSERT_EQ(av.Last(5).Length(), 5U);
+  }
+
+#if 0
+        {
+            Span<int, 5> av = arr;
+#  ifdef CONFIRM_COMPILATION_ERRORS
+            ASSERT_EQ(av.Last<6>().Length() , 6U);
+#  endif
+            CHECK_THROW(av.Last(6).Length(), fail_fast);
+        }
+#endif
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.Last<0>().Length(), 0U);
+    ASSERT_EQ(av.Last(0).Length(), 0U);
+  }
+}
+
+SPAN_TEST(from_to) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(3).Length(), 2U);
+    ASSERT_EQ(av.From(2)[1], 4);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(5).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(0).Length(), 5U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(3).Length(), 3U);
+    ASSERT_EQ(av.To(3)[1], 2);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(5).Length(), 5U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(1, 4).Length(), 3U);
+    ASSERT_EQ(av.FromTo(1, 4)[1], 3);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(2, 2).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(0, 5).Length(), 5U);
+  }
+}
+
+SPAN_TEST(Subspan) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<2, 2>().Length()), 2U);
+    ASSERT_EQ(av.Subspan(2, 2).Length(), 2U);
+    ASSERT_EQ(av.Subspan(2, 3).Length(), 3U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<0, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(0, 0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<0, 5>().Length()), 5U);
+    ASSERT_EQ(av.Subspan(0, 5).Length(), 5U);
+    CHECK_THROW(av.Subspan(0, 6).Length(), fail_fast);
+    CHECK_THROW(av.Subspan(1, 5).Length(), fail_fast);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<4, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(4, 0).Length(), 0U);
+    ASSERT_EQ(av.Subspan(5, 0).Length(), 0U);
+    CHECK_THROW(av.Subspan(6, 0).Length(), fail_fast);
+  }
+
+  {
+    Span<int> av;
+    ASSERT_EQ((av.Subspan<0, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(0, 0).Length(), 0U);
+    CHECK_THROW((av.Subspan<1, 0>().Length()), fail_fast);
+  }
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.Subspan(0).Length(), 0U);
+    CHECK_THROW(av.Subspan(1).Length(), fail_fast);
+  }
+
+  {
+    Span<int> av = arr;
+    ASSERT_EQ(av.Subspan(0).Length(), 5U);
+    ASSERT_EQ(av.Subspan(1).Length(), 4U);
+    ASSERT_EQ(av.Subspan(4).Length(), 1U);
+    ASSERT_EQ(av.Subspan(5).Length(), 0U);
+    CHECK_THROW(av.Subspan(6).Length(), fail_fast);
+    auto av2 = av.Subspan(1);
+    for (int i = 0; i < 4; ++i) ASSERT_EQ(av2[i], i + 2);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Subspan(0).Length(), 5U);
+    ASSERT_EQ(av.Subspan(1).Length(), 4U);
+    ASSERT_EQ(av.Subspan(4).Length(), 1U);
+    ASSERT_EQ(av.Subspan(5).Length(), 0U);
+    CHECK_THROW(av.Subspan(6).Length(), fail_fast);
+    auto av2 = av.Subspan(1);
+    for (int i = 0; i < 4; ++i) ASSERT_EQ(av2[i], i + 2);
+  }
+}
+
+SPAN_TEST(at_call) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s = arr;
+    ASSERT_EQ(s.at(0), 1);
+    CHECK_THROW(s.at(5), fail_fast);
+  }
+
+  {
+    int arr2d[2] = {1, 6};
+    Span<int, 2> s = arr2d;
+    ASSERT_EQ(s.at(0), 1);
+    ASSERT_EQ(s.at(1), 6);
+    CHECK_THROW(s.at(2), fail_fast);
+  }
+}
+
+SPAN_TEST(operator_function_call) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s = arr;
+    ASSERT_EQ(s(0), 1);
+    CHECK_THROW(s(5), fail_fast);
+  }
+
+  {
+    int arr2d[2] = {1, 6};
+    Span<int, 2> s = arr2d;
+    ASSERT_EQ(s(0), 1);
+    ASSERT_EQ(s(1), 6);
+    CHECK_THROW(s(2), fail_fast);
+  }
+}
+
+SPAN_TEST(iterator_default_init) {
+  Span<int>::iterator it1;
+  Span<int>::iterator it2;
+  ASSERT_EQ(it1, it2);
+}
+
+SPAN_TEST(const_iterator_default_init) {
+  Span<int>::const_iterator it1;
+  Span<int>::const_iterator it2;
+  ASSERT_EQ(it1, it2);
+}
+
+SPAN_TEST(iterator_conversions) {
+  Span<int>::iterator badIt;
+  Span<int>::const_iterator badConstIt;
+  ASSERT_EQ(badIt, badConstIt);
+
+  int a[] = {1, 2, 3, 4};
+  Span<int> s = a;
+
+  auto it = s.begin();
+  auto cit = s.cbegin();
+
+  ASSERT_EQ(it, cit);
+  ASSERT_EQ(cit, it);
+
+  Span<int>::const_iterator cit2 = it;
+  ASSERT_EQ(cit2, cit);
+
+  Span<int>::const_iterator cit3 = it + 4;
+  ASSERT_EQ(cit3, s.cend());
+}
+
+SPAN_TEST(iterator_comparisons) {
+  int a[] = {1, 2, 3, 4};
+  {
+    Span<int> s = a;
+    Span<int>::iterator it = s.begin();
+    auto it2 = it + 1;
+    Span<int>::const_iterator cit = s.cbegin();
+
+    ASSERT_EQ(it, cit);
+    ASSERT_EQ(cit, it);
+    ASSERT_EQ(it, it);
+    ASSERT_EQ(cit, cit);
+    ASSERT_EQ(cit, s.begin());
+    ASSERT_EQ(s.begin(), cit);
+    ASSERT_EQ(s.cbegin(), cit);
+    ASSERT_EQ(it, s.begin());
+    ASSERT_EQ(s.begin(), it);
+
+    ASSERT_NE(it, it2);
+    ASSERT_NE(it2, it);
+    ASSERT_NE(it, s.end());
+    ASSERT_NE(it2, s.end());
+    ASSERT_NE(s.end(), it);
+    ASSERT_NE(it2, cit);
+    ASSERT_NE(cit, it2);
+
+    ASSERT_LT(it, it2);
+    ASSERT_LE(it, it2);
+    ASSERT_LE(it2, s.end());
+    ASSERT_LT(it, s.end());
+    ASSERT_LE(it, cit);
+    ASSERT_LE(cit, it);
+    ASSERT_LT(cit, it2);
+    ASSERT_LE(cit, it2);
+    ASSERT_LT(cit, s.end());
+    ASSERT_LE(cit, s.end());
+
+    ASSERT_GT(it2, it);
+    ASSERT_GE(it2, it);
+    ASSERT_GT(s.end(), it2);
+    ASSERT_GE(s.end(), it2);
+    ASSERT_GT(it2, cit);
+    ASSERT_GE(it2, cit);
+  }
+}
+
+SPAN_TEST(begin_end) {
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    Span<int>::iterator it = s.begin();
+    Span<int>::iterator it2 = std::begin(s);
+    ASSERT_EQ(it, it2);
+
+    it = s.end();
+    it2 = std::end(s);
+    ASSERT_EQ(it, it2);
+  }
+
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.begin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 1);
+
+    auto beyond = s.end();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4);
+    ASSERT_EQ(first - first, 0);
+    ASSERT_EQ(beyond - beyond, 0);
+
+    ++it;
+    ASSERT_EQ(it - first, 1);
+    ASSERT_EQ(*it, 2);
+    *it = 22;
+    ASSERT_EQ(*it, 22);
+    ASSERT_EQ(beyond - it, 3);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.end()) {
+      *it = 5;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0);
+
+    for (auto& n : s) {
+      ASSERT_EQ(n, 5);
+    }
+  }
+}
+
+SPAN_TEST(cbegin_cend) {
+#if 0
+          {
+              int a[] = { 1, 2, 3, 4 };
+              Span<int> s = a;
+
+              Span<int>::const_iterator cit = s.cbegin();
+              Span<int>::const_iterator cit2 = std::cbegin(s);
+              ASSERT_EQ(cit , cit2);
+
+              cit = s.cend();
+              cit2 = std::cend(s);
+              ASSERT_EQ(cit , cit2);
+          }
+#endif
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.cbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 1);
+
+    auto beyond = s.cend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4);
+    ASSERT_EQ(first - first, 0);
+    ASSERT_EQ(beyond - beyond, 0);
+
+    ++it;
+    ASSERT_EQ(it - first, 1);
+    ASSERT_EQ(*it, 2);
+    ASSERT_EQ(beyond - it, 3);
+
+    int last = 0;
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.cend()) {
+      ASSERT_EQ(*it, last + 1);
+
+      last = *it;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0);
+  }
+}
+
+SPAN_TEST(rbegin_rend) {
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.rbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 4);
+
+    auto beyond = s.rend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4);
+    ASSERT_EQ(first - first, 0);
+    ASSERT_EQ(beyond - beyond, 0);
+
+    ++it;
+    ASSERT_EQ(it - first, 1);
+    ASSERT_EQ(*it, 3);
+    *it = 22;
+    ASSERT_EQ(*it, 22);
+    ASSERT_EQ(beyond - it, 3);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.rend()) {
+      *it = 5;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0);
+
+    for (auto& n : s) {
+      ASSERT_EQ(n, 5);
+    }
+  }
+}
+
+SPAN_TEST(crbegin_crend) {
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.crbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 4);
+
+    auto beyond = s.crend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4);
+    ASSERT_EQ(first - first, 0);
+    ASSERT_EQ(beyond - beyond, 0);
+
+    ++it;
+    ASSERT_EQ(it - first, 1);
+    ASSERT_EQ(*it, 3);
+    ASSERT_EQ(beyond - it, 3);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    int last = 5;
+    while (it != s.crend()) {
+      ASSERT_EQ(*it, last - 1);
+      last = *it;
+
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0);
+  }
+}
+
+SPAN_TEST(comparison_operators) {
+  {
+    Span<int> s1 = nullptr;
+    Span<int> s2 = nullptr;
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = {2, 1};
+    Span<int> s1 = arr;
+    Span<int> s2 = arr;
+
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = {2, 1};  // bigger
+
+    Span<int> s1 = nullptr;
+    Span<int> s2 = arr;
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+
+  {
+    int arr1[] = {1, 2};
+    int arr2[] = {1, 2};
+    Span<int> s1 = arr1;
+    Span<int> s2 = arr2;
+
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = {1, 2, 3};
+
+    AssertSpanOfThreeInts(arr);
+
+    Span<int> s1 = {&arr[0], 2};  // shorter
+    Span<int> s2 = arr;           // longer
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+
+  {
+    int arr1[] = {1, 2};  // smaller
+    int arr2[] = {2, 1};  // bigger
+
+    Span<int> s1 = arr1;
+    Span<int> s2 = arr2;
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+}
+
+SPAN_TEST(as_bytes) {
+  int a[] = {1, 2, 3, 4};
+
+  {
+    Span<const int> s = a;
+    ASSERT_EQ(s.Length(), 4U);
+    Span<const uint8_t> bs = AsBytes(s);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+
+  {
+    Span<int> s;
+    auto bs = AsBytes(s);
+    ASSERT_EQ(bs.Length(), s.Length());
+    ASSERT_EQ(bs.Length(), 0U);
+    ASSERT_EQ(bs.size_bytes(), 0U);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.data(), reinterpret_cast<const uint8_t*>(SLICE_INT_PTR));
+  }
+
+  {
+    Span<int> s = a;
+    auto bs = AsBytes(s);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+}
+
+SPAN_TEST(as_writable_bytes) {
+  int a[] = {1, 2, 3, 4};
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    // you should not be able to get writeable bytes for const objects
+    Span<const int> s = a;
+    ASSERT_EQ(s.Length(), 4U);
+    Span<const byte> bs = AsWritableBytes(s);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+#endif
+  }
+
+  {
+    Span<int> s;
+    auto bs = AsWritableBytes(s);
+    ASSERT_EQ(bs.Length(), s.Length());
+    ASSERT_EQ(bs.Length(), 0U);
+    ASSERT_EQ(bs.size_bytes(), 0U);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.data(), reinterpret_cast<uint8_t*>(SLICE_INT_PTR));
+  }
+
+  {
+    Span<int> s = a;
+    auto bs = AsWritableBytes(s);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+}
+
+SPAN_TEST(as_chars) {
+  const uint8_t a[] = {1, 2, 3, 4};
+  Span<const uint8_t> u = Span(a);
+  Span<const char> c = AsChars(u);
+  ASSERT_EQ(static_cast<const void*>(u.data()),
+            static_cast<const void*>(c.data()));
+  ASSERT_EQ(u.size(), c.size());
+}
+
+SPAN_TEST(as_writable_chars) {
+  uint8_t a[] = {1, 2, 3, 4};
+  Span<uint8_t> u = Span(a);
+  Span<char> c = AsWritableChars(u);
+  ASSERT_EQ(static_cast<void*>(u.data()), static_cast<void*>(c.data()));
+  ASSERT_EQ(u.size(), c.size());
+}
+
+SPAN_TEST(fixed_size_conversions) {
+  int arr[] = {1, 2, 3, 4};
+
+  // converting to an Span from an equal size array is ok
+  Span<int, 4> s4 = arr;
+  ASSERT_EQ(s4.Length(), 4U);
+
+  // converting to dynamic_range is always ok
+  {
+    Span<int> s = s4;
+    ASSERT_EQ(s.Length(), s4.Length());
+    static_cast<void>(s);
+  }
+
+// initialization or assignment to static Span that REDUCES size is NOT ok
+#ifdef CONFIRM_COMPILATION_ERRORS
+  { Span<int, 2> s = arr; }
+  {
+    Span<int, 2> s2 = s4;
+    static_cast<void>(s2);
+  }
+#endif
+
+#if 0
+        // even when done dynamically
+        {
+            Span<int> s = arr;
+            auto f = [&]() {
+                Span<int, 2> s2 = s;
+                static_cast<void>(s2);
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+#endif
+
+  // but doing so explicitly is ok
+
+  // you can convert statically
+  {
+    Span<int, 2> s2 = {arr, 2};
+    static_cast<void>(s2);
+  }
+  {
+    Span<int, 1> s1 = s4.First<1>();
+    static_cast<void>(s1);
+  }
+
+  // ...or dynamically
+  {
+    // NB: implicit conversion to Span<int,1> from Span<int>
+    Span<int, 1> s1 = s4.First(1);
+    static_cast<void>(s1);
+  }
+
+#if 0
+        // initialization or assignment to static Span that requires size INCREASE is not ok.
+        int arr2[2] = {1, 2};
+#endif
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  { Span<int, 4> s3 = arr2; }
+  {
+    Span<int, 2> s2 = arr2;
+    Span<int, 4> s4a = s2;
+  }
+#endif
+
+#if 0
+        {
+            auto f = [&]() {
+                Span<int, 4> _s4 = {arr2, 2};
+                static_cast<void>(_s4);
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+
+        // this should fail - we are trying to assign a small dynamic Span to a fixed_size larger one
+        Span<int> av = arr2;
+        auto f = [&]() {
+            Span<int, 4> _s4 = av;
+            static_cast<void>(_s4);
+        };
+        CHECK_THROW(f(), fail_fast);
+#endif
+}
+
+#if 0
+    SPAN_TEST(interop_with_std_regex)
+    {
+        char lat[] = { '1', '2', '3', '4', '5', '6', 'E', 'F', 'G' };
+        Span<char> s = lat;
+        auto f_it = s.begin() + 7;
+
+        std::match_results<Span<char>::iterator> match;
+
+        std::regex_match(s.begin(), s.end(), match, std::regex(".*"));
+        ASSERT_EQ(match.ready());
+        ASSERT_TRUE(!match.empty());
+        ASSERT_TRUE(match[0].matched);
+        ASSERT_TRUE(match[0].first , s.begin());
+        ASSERT_EQ(match[0].second , s.end());
+
+        std::regex_search(s.begin(), s.end(), match, std::regex("F"));
+        ASSERT_TRUE(match.ready());
+        ASSERT_TRUE(!match.empty());
+        ASSERT_TRUE(match[0].matched);
+        ASSERT_EQ(match[0].first , f_it);
+        ASSERT_EQ(match[0].second , (f_it + 1));
+    }
+
+SPAN_TEST(interop_with_gsl_at)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+  Span<int> s{ arr };
+  ASSERT_EQ(at(s, 0) , 1 );
+ASSERT_EQ(at(s, 1) , 2U);
+}
+#endif
+
+SPAN_TEST(default_constructible) {
+  ASSERT_TRUE((std::is_default_constructible<Span<int>>::value));
+  ASSERT_TRUE((std::is_default_constructible<Span<int, 0>>::value));
+  ASSERT_TRUE((!std::is_default_constructible<Span<int, 42>>::value));
+}
+
+SPAN_TEST(type_inference) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto s = Span{arr};
+  static_assert(std::is_same_v<const Span<const int, 5>, decltype(s)>);
+  static_assert(arr == s.Elements());
+}
+
+SPAN_TEST(split_at_dynamic_with_dynamic_extent) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr Span<const int> s = Span{arr};
+
+  {  // Split at begin.
+    constexpr auto splitAt0Result = s.SplitAt(0);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt0Result.second.Elements());
+    ASSERT_EQ(0u, splitAt0Result.first.Length());
+    ASSERT_EQ(5u, splitAt0Result.second.Length());
+  }
+
+  {  // Split at end.
+    constexpr auto splitAt5Result = s.SplitAt(s.Length());
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt5Result.first.Elements());
+    ASSERT_EQ(5u, splitAt5Result.first.Length());
+    ASSERT_EQ(0u, splitAt5Result.second.Length());
+  }
+
+  {
+    // Split inside.
+    constexpr auto splitAt3Result = s.SplitAt(3);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt3Result.first.Elements());
+    ASSERT_EQ(s.Elements() + 3, splitAt3Result.second.Elements());
+    ASSERT_EQ(3u, splitAt3Result.first.Length());
+    ASSERT_EQ(2u, splitAt3Result.second.Length());
+  }
+}
+
+SPAN_TEST(split_at_dynamic_with_static_extent) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto s = Span{arr};
+
+  {
+    // Split at begin.
+    constexpr auto splitAt0Result = s.SplitAt(0);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt0Result.second.Elements());
+  }
+
+  {
+    // Split at end.
+    constexpr auto splitAt5Result = s.SplitAt(s.Length());
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt5Result.first.Elements());
+  }
+
+  {
+    // Split inside.
+    constexpr auto splitAt3Result = s.SplitAt(3);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt3Result.first.Elements());
+    ASSERT_EQ(s.Elements() + 3, splitAt3Result.second.Elements());
+  }
+}
+
+SPAN_TEST(split_at_static) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto s = Span{arr};
+
+  // Split at begin.
+  constexpr auto splitAt0Result = s.SplitAt<0>();
+  static_assert(
+      std::is_same_v<Span<const int, 0>, decltype(splitAt0Result.first)>);
+  static_assert(
+      std::is_same_v<Span<const int, 5>, decltype(splitAt0Result.second)>);
+  static_assert(splitAt0Result.second.Elements() == s.Elements());
+
+  // Split at end.
+  constexpr auto splitAt5Result = s.SplitAt<s.Length()>();
+  static_assert(std::is_same_v<Span<const int, s.Length()>,
+                               decltype(splitAt5Result.first)>);
+  static_assert(
+      std::is_same_v<Span<const int, 0>, decltype(splitAt5Result.second)>);
+  static_assert(splitAt5Result.first.Elements() == s.Elements());
+
+  // Split inside.
+  constexpr auto splitAt3Result = s.SplitAt<3>();
+  static_assert(
+      std::is_same_v<Span<const int, 3>, decltype(splitAt3Result.first)>);
+  static_assert(
+      std::is_same_v<Span<const int, 2>, decltype(splitAt3Result.second)>);
+  static_assert(splitAt3Result.first.Elements() == s.Elements());
+  static_assert(splitAt3Result.second.Elements() == s.Elements() + 3);
+}
+
+SPAN_TEST(as_const_dynamic) {
+  static int arr[5] = {1, 2, 3, 4, 5};
+  auto span = Span{arr, 5};
+  auto constSpan = span.AsConst();
+  static_assert(std::is_same_v<Span<const int>, decltype(constSpan)>);
+}
+
+SPAN_TEST(as_const_static) {
+  {
+    static constexpr int constArr[5] = {1, 2, 3, 4, 5};
+    constexpr auto span = Span{constArr};  // is already a Span<const int>
+    constexpr auto constSpan = span.AsConst();
+
+    static_assert(
+        std::is_same_v<const Span<const int, 5>, decltype(constSpan)>);
+  }
+
+  {
+    static int arr[5] = {1, 2, 3, 4, 5};
+    auto span = Span{arr};
+    auto constSpan = span.AsConst();
+    static_assert(std::is_same_v<Span<const int, 5>, decltype(constSpan)>);
+  }
+}
+
+SPAN_TEST(construct_from_iterators_dynamic) {
+  const int constArr[5] = {1, 2, 3, 4, 5};
+  auto constSpan = Span{constArr};
+
+  // const from const
+  {
+    const auto wholeSpan = Span{constSpan.cbegin(), constSpan.cend()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<const int>>);
+    ASSERT_TRUE(constSpan == wholeSpan);
+
+    const auto emptyBeginSpan = Span{constSpan.cbegin(), constSpan.cbegin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{constSpan.cend(), constSpan.cend()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{constSpan.cbegin() + 1, constSpan.cend() - 1};
+    ASSERT_EQ(constSpan.Length() - 2, subSpan.Length());
+    ASSERT_EQ(constSpan.Elements() + 1, subSpan.Elements());
+  }
+
+  int arr[5] = {1, 2, 3, 4, 5};
+  auto span = Span{arr};
+
+  // const from non-const
+  {
+    const auto wholeSpan = Span{span.cbegin(), span.cend()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<const int>>);
+    // XXX Can't use span == wholeSpan because of difference in constness.
+    ASSERT_EQ(span.Elements(), wholeSpan.Elements());
+    ASSERT_EQ(span.Length(), wholeSpan.Length());
+
+    const auto emptyBeginSpan = Span{span.cbegin(), span.cbegin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{span.cend(), span.cend()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{span.cbegin() + 1, span.cend() - 1};
+    ASSERT_EQ(span.Length() - 2, subSpan.Length());
+    ASSERT_EQ(span.Elements() + 1, subSpan.Elements());
+  }
+
+  // non-const from non-const
+  {
+    const auto wholeSpan = Span{span.begin(), span.end()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<int>>);
+    ASSERT_TRUE(span == wholeSpan);
+
+    const auto emptyBeginSpan = Span{span.begin(), span.begin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{span.end(), span.end()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{span.begin() + 1, span.end() - 1};
+    ASSERT_EQ(span.Length() - 2, subSpan.Length());
+  }
+}
+
+SPAN_TEST(construct_from_iterators_static) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto constSpan = Span{arr};
+
+  // const
+  {
+    const auto wholeSpan = Span{constSpan.cbegin(), constSpan.cend()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<const int>>);
+    ASSERT_TRUE(constSpan == wholeSpan);
+
+    const auto emptyBeginSpan = Span{constSpan.cbegin(), constSpan.cbegin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{constSpan.cend(), constSpan.cend()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{constSpan.cbegin() + 1, constSpan.cend() - 1};
+    ASSERT_EQ(constSpan.Length() - 2, subSpan.Length());
+    ASSERT_EQ(constSpan.Elements() + 1, subSpan.Elements());
+  }
+}
+
+SPAN_TEST(construct_from_container_with_type_deduction) {
+  std::vector<int> vec = {1, 2, 3, 4, 5};
+
+  // from const
+  {
+    const auto& constVecRef = vec;
+
+    auto span = Span{constVecRef};
+    static_assert(std::is_same_v<decltype(span), Span<const int>>);
+  }
+
+  // from non-const
+  {
+    auto span = Span{vec};
+    static_assert(std::is_same_v<decltype(span), Span<int>>);
+  }
+}
-- 
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