From c143a07f61f5e1cb2be8e3f7676ae869efd18e7c Mon Sep 17 00:00:00 2001
From: Casey Carter <Casey@Carter.net>
Date: Thu, 28 May 2020 18:00:40 -0700
Subject: [PATCH] Add string_view test case and modify deduction guides

---
 include/gsl/span     | 10 ++++++----
 tests/span_tests.cpp | 16 ++++++++++++++++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/include/gsl/span b/include/gsl/span
index c7b45e9..3022e0d 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -740,11 +740,13 @@ span(std::array<Type, Size>&)->span<Type, Size>;
 template <class Type, std::size_t Size>
 span(const std::array<Type, Size>&)->span<const Type, Size>;
 
-template <class Container>
-span(Container&)->span<typename Container::value_type>;
+template <class Container,
+    class Element = std::remove_pointer_t<decltype(std::declval<Container&>().data())>>
+span(Container&)->span<Element>;
 
-template <class Container>
-span(const Container&)->span<const typename Container::value_type>;
+template <class Container,
+    class Element = std::remove_pointer_t<decltype(std::declval<const Container&>().data())>>
+span(const Container&)->span<Element>;
 
 #endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
 
diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index f53518b..d27d645 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -31,6 +31,13 @@
 #include <vector>      // for vector
 #include <utility>
 
+#ifdef __has_include
+#if __has_include(<string_view>)
+#include <string_view>
+#define HAS_STRING_VIEW
+#endif
+#endif
+
 using namespace std;
 using namespace gsl;
 
@@ -1234,11 +1241,20 @@ TEST(span_test, from_array_constructor)
     {
         std::vector v{1,2,3,4};
         gsl::span sp{v};
+        static_assert(std::is_same<decltype(sp), gsl::span<int>>::value);
     }
     {
         std::string str{"foo"};
         gsl::span sp{str};
+        static_assert(std::is_same<decltype(sp), gsl::span<char>>::value);
     }
+#ifdef HAS_STRING_VIEW
+    {
+        std::string_view sv{"foo"};
+        gsl::span sp{sv};
+        static_assert(std::is_same<decltype(sp), gsl::span<const char>>::value);
+    }
+#endif
 #endif
  }