From a49ff1b8df978c1b80738cab3bb25b4140fa6424 Mon Sep 17 00:00:00 2001
From: "Jordan Maples [MSFT]" <49793787+JordanMaples@users.noreply.github.com>
Date: Wed, 5 Feb 2020 17:12:31 -0800
Subject: [PATCH] update span specialization of at, change some tests back to
 int i with narrowing for the comparisons.

---
 include/gsl/span     |  3 ++-
 tests/span_tests.cpp | 18 +++++++++---------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/include/gsl/span b/include/gsl/span
index ecbca5d..b922576 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -806,7 +806,8 @@ template <class ElementType, std::size_t Extent>
 constexpr ElementType& at(span<ElementType, Extent> s, index i)
 {
     // No bounds checking here because it is done in span::operator[] called below
-    return s[i];
+    Ensures(i >= 0);
+    return s[narrow_cast<std::size_t>(i)];
 }
 
 // [span.obs] Free observer functions
diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index 5d9c18b..790cee0 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -153,24 +153,24 @@ TEST(span_test, from_pointer_length_constructor)
     int arr[4] = {1, 2, 3, 4};
 
     {
-        for (std::size_t i = 0; i < 4; ++i)
+        for (int i = 0; i < 4; ++i)
         {
             {
-                span<int> s = {&arr[0], i};
-                EXPECT_TRUE(s.size() == i);
+                span<int> s = {&arr[0], narrow_cast<std::size_t>(i)};
+                EXPECT_TRUE(s.size() == narrow_cast<std::size_t>(i));
                 EXPECT_TRUE(s.data() == &arr[0]);
                 EXPECT_TRUE(s.empty() == (i == 0));
-                for (std::size_t j = 0; j < i; ++j)
-                    EXPECT_TRUE(arr[j] == s[j]);
+                for (int j = 0; j < i; ++j)
+                    EXPECT_TRUE(arr[j] == s[narrow_cast<std::size_t>(j)]);
             }
             {
-                span<int> s = {&arr[i], 4 - i};
-                EXPECT_TRUE(s.size() == 4 - i);
+                span<int> s = {&arr[i], 4 - narrow_cast<std::size_t>(i)};
+                EXPECT_TRUE(s.size() == 4 - narrow_cast<std::size_t>(i));
                 EXPECT_TRUE(s.data() == &arr[i]);
                 EXPECT_TRUE(s.empty() == ((4 - i) == 0));
 
-                for (std::size_t j = 0; j < 4 - i; ++j)
-                    EXPECT_TRUE(arr[j + i] == s[j]);
+                for (int j = 0; j < 4 - i; ++j)
+                    EXPECT_TRUE(arr[j + i] == s[narrow_cast<std::size_t>(j)]);
             }
         }
     }