Removed workaround for GCC4

Author: JohanMabille

include/xtensor/containers/xstorage.hpp

@@ -1437,49 +1437,6 @@ namespace xt
 #define XTENSOR_CONST const
 #endif
 
-#if defined(__GNUC__) && __GNUC__ < 5 && !defined(__clang__)
-#define GCC4_FALLBACK
-
-    namespace const_array_detail
-    {
-        template <class T, std::size_t N>
-        struct array_traits
-        {
-            using storage_type = T[N];
-
-            static constexpr T& ref(const storage_type& t, std::size_t n) noexcept
-            {
-                return const_cast<T&>(t[n]);
-            }
-
-            static constexpr T* ptr(const storage_type& t) noexcept
-            {
-                return const_cast<T*>(t);
-            }
-        };
-
-        template <class T>
-        struct array_traits<T, 0>
-        {
-            struct empty
-            {
-            };
-
-            using storage_type = empty;
-
-            static constexpr T& ref(const storage_type& /*t*/, std::size_t /*n*/) noexcept
-            {
-                return *static_cast<T*>(nullptr);
-            }
-
-            static constexpr T* ptr(const storage_type& /*t*/) noexcept
-            {
-                return nullptr;
-            }
-        };
-    }
-#endif
-
     /**
      * A std::array like class with all member function (except reverse iterators)
      * as constexpr. The data is immutable once set.
@@ -1502,11 +1459,7 @@ namespace xt
 
         constexpr const_reference operator[](std::size_t idx) const
         {
-#ifdef GCC4_FALLBACK
-            return const_array_detail::array_traits<T, N>::ref(m_data, idx);
-#else
             return m_data[idx];
-#endif
         }
 
         constexpr const_iterator begin() const noexcept
@@ -1552,30 +1505,17 @@ namespace xt
 
         constexpr const_pointer data() const noexcept
         {
-#ifdef GCC4_FALLBACK
-            return const_array_detail::array_traits<T, N>::ptr(m_data);
-#else
             return m_data;
-#endif
         }
 
         constexpr const_reference front() const noexcept
         {
-#ifdef GCC4_FALLBACK
-            return const_array_detail::array_traits<T, N>::ref(m_data, 0);
-#else
             return m_data[0];
-#endif
         }
 
         constexpr const_reference back() const noexcept
         {
-#ifdef GCC4_FALLBACK
-            return N ? const_array_detail::array_traits<T, N>::ref(m_data, N - 1)
-                     : const_array_detail::array_traits<T, N>::ref(m_data, 0);
-#else
             return m_data[size() - 1];
-#endif
         }
 
         constexpr bool empty() const noexcept
@@ -1588,14 +1528,9 @@ namespace xt
             return N;
         }
 
-#ifdef GCC4_FALLBACK
-        XTENSOR_CONST typename const_array_detail::array_traits<T, N>::storage_type m_data;
-#else
         XTENSOR_CONST T m_data[N > 0 ? N : 1];
-#endif
     };
 
-#undef GCC4_FALLBACK
 
     template <class T, std::size_t N>
     inline bool operator==(const const_array<T, N>& lhs, const const_array<T, N>& rhs)