Merge d988e0e19ba5fa75e4904e716121dd7215f38a4f into 87f9d768866548b5b86e72be66c60c5abd4d9b37

include/gsl/span

@@ -140,9 +140,7 @@ namespace details
 
         constexpr span_iterator(pointer begin, pointer end, pointer current)
             : begin_(begin), end_(end), current_(current)
-        {
-            Expects(begin_ <= current_ && current <= end_);
-        }
+        {}
 
         constexpr operator span_iterator<const Type>() const noexcept
         {
@@ -151,18 +149,21 @@ namespace details
 
         constexpr reference operator*() const noexcept
         {
-            Expects(current_ != end_);
+            Expects(begin_ && end_);
+            Expects(begin_ <= current_ && current_ < end_);
             return *current_;
         }
 
         constexpr pointer operator->() const noexcept
         {
-            Expects(current_ != end_);
+            Expects(begin_ && end_);
+            Expects(begin_ <= current_ && current_ < end_);
             return current_;
         }
         constexpr span_iterator& operator++() noexcept
         {
-            Expects(current_ != end_);
+            Expects(begin_ && current_ && end_);
+            Expects(current_ < end_);
             // clang-format off
             GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
             // clang-format on
@@ -179,7 +180,8 @@ namespace details
 
         constexpr span_iterator& operator--() noexcept
         {
-            Expects(begin_ != current_);
+            Expects(begin_ && end_);
+            Expects(begin_ < current_);
             --current_;
             return *this;
         }