span constructor no address (#723)

* Changed &arr[0] to std::array<T, N>::data and std::address_of to protect against overloaded operator&.

* Removed the usage of `std::addressof` because it is a C++ 17 feature. Using decay for C arrays instead.

* Add unit tests for #662.

* Added c++17 test configurations for clang5.0 and clang6.0

* fixed CppCoreCheck pointer decay warning

Author: Anna Gringauze

include/gsl/span

@@ -29,6 +29,7 @@
 #include <stdexcept>
 #include <type_traits> // for enable_if_t, declval, is_convertible, inte...
 #include <utility>
+#include <memory> // for std::addressof
 
 #ifdef _MSC_VER
 #pragma warning(push)
@@ -390,19 +391,19 @@ public:
 
     template <std::size_t N>
     constexpr span(element_type (&arr)[N]) noexcept
-        : storage_(KnownNotNull{&arr[0]}, details::extent_type<N>())
+        : storage_(KnownNotNull{std::addressof(arr[0])}, details::extent_type<N>())
     {}
 
     template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
     // GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute // TODO: parser bug
     constexpr span(std::array<ArrayElementType, N>& arr) noexcept
-        : storage_(&arr[0], details::extent_type<N>())
+        : storage_(arr.data(), details::extent_type<N>())
     {}
 
     template <std::size_t N>
     // GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute // TODO: parser bug
     constexpr span(const std::array<std::remove_const_t<element_type>, N>& arr) noexcept
-        : storage_(&arr[0], details::extent_type<N>())
+        : storage_(arr.data(), details::extent_type<N>())
     {}
 
     // NB: the SFINAE here uses .data() as a incomplete/imperfect proxy for the requirement

tests/span_tests.cpp

@@ -52,6 +52,10 @@ struct BaseClass
 struct DerivedClass : BaseClass
 {
 };
+struct AddressOverloaded
+{
+    AddressOverloaded operator&() const { return {}; }
+};
 }
 
 GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
@@ -306,19 +310,17 @@ TEST_CASE("from_pointer_pointer_constructor")
     }
 }
 
-GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
-GSL_SUPPRESS(bounds.3) // NO-FORMAT: attribute // TODO: false positive?
 TEST_CASE("from_array_constructor")
 {
     int arr[5] = {1, 2, 3, 4, 5};
 
     {
-        span<int> s{arr};
+        const span<int> s{arr};
         CHECK((s.size() == 5 && s.data() == &arr[0]));
     }
 
     {
-        span<int, 5> s{arr};
+        const span<int, 5> s{arr};
         CHECK((s.size() == 5 && s.data() == &arr[0]));
     }
 
@@ -350,8 +352,8 @@ TEST_CASE("from_array_constructor")
     }
 #endif
     {
-        span<int[3]> s{&arr2d[0], 1};
-        CHECK((s.size() == 1 && s.data() == &arr2d[0]));
+        const span<int[3]> s{std::addressof(arr2d[0]), 1};
+        CHECK((s.size() == 1 && s.data() == std::addressof(arr2d[0])));
     }
 
     int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
@@ -379,24 +381,32 @@ TEST_CASE("from_array_constructor")
     }
 #endif
     {
-        span<int[3][2]> s{&arr3d[0], 1};
-        CHECK((s.size() == 1 && s.data() == &arr3d[0]));
+        const span<int[3][2]> s{std::addressof(arr3d[0]), 1};
+        CHECK((s.size() == 1 && s.data() == std::addressof(arr3d[0])));
     }
 
     {
-        auto s = make_span(arr);
-        CHECK((s.size() == 5 && s.data() == &arr[0]));
+        const auto s = make_span(arr);
+        CHECK((s.size() == 5 && s.data() == std::addressof(arr[0])));
+    }
+
+    {
+        const auto s = make_span(std::addressof(arr2d[0]), 1);
+        CHECK((s.size() == 1 && s.data() == std::addressof(arr2d[0])));
     }
 
     {
-        auto s = make_span(&(arr2d[0]), 1);
-        CHECK((s.size() == 1 && s.data() == &arr2d[0]));
+        const auto s = make_span(std::addressof(arr3d[0]), 1);
+        CHECK((s.size() == 1 && s.data() == std::addressof(arr3d[0])));
     }
 
+    AddressOverloaded ao_arr[5] = {};
+
     {
-        auto s = make_span(&arr3d[0], 1);
-        CHECK((s.size() == 1 && s.data() == &arr3d[0]));
+        const span<AddressOverloaded, 5> s{ao_arr};
+        CHECK((s.size() == 5 && s.data() == std::addressof(ao_arr[0])));
     }
+
 }
 
 GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
@@ -442,6 +452,13 @@ TEST_CASE("from_std_array_constructor")
         CHECK((cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data()));
     }
 
+    std::array<AddressOverloaded, 4> ao_arr{};  
+
+    {
+        span<AddressOverloaded, 4> fs{ao_arr};
+        CHECK((fs.size() == narrow_cast<ptrdiff_t>(ao_arr.size()) && ao_arr.data() == fs.data()));
+    }
+
 #ifdef CONFIRM_COMPILATION_ERRORS
     {
         span<int, 2> s{arr};
@@ -516,6 +533,13 @@ TEST_CASE("from_const_std_array_constructor")
         CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
     }
 
+    const std::array<AddressOverloaded, 4> ao_arr{};
+
+    {
+        span<const AddressOverloaded, 4> s{ao_arr};
+        CHECK((s.size() == narrow_cast<ptrdiff_t>(ao_arr.size()) && s.data() == ao_arr.data()));
+    }
+
 #ifdef CONFIRM_COMPILATION_ERRORS
     {
         span<const int, 2> s{arr};