Release 0.9.2 fixes #64

Note: With MSVC Debug, a span cannot be created from an empty range,
like: std::vector v; span(v.begin(),v.end()).

This behaviour is present since the introduction of construction from iterators in v0.9.0.

Author: martinmoene

include/nonstd/span.hpp

@@ -1299,6 +1299,8 @@ class span
 
 private:
 
+    // Note: C++20 has std::pointer_traits<Ptr>::to_address( it );
+
 #if span_HAVE( ITERATOR_CTOR )
     static inline span_constexpr pointer to_address( std::nullptr_t ) span_noexcept
     {

test/span-main.t.cpp

@@ -155,6 +155,18 @@ CASE( "Presence of C++ language features" "[.stdlanguage]" )
     span_ABSENT(  _CPPUNWIND );
 #endif
 
+#if defined(_DEBUG)
+    span_PRESENT( _DEBUG );
+#else
+    span_ABSENT(  _DEBUG );
+#endif
+
+#if defined(NDEBUG)
+    span_PRESENT( NDEBUG );
+#else
+    span_ABSENT(  NDEBUG );
+#endif
+
 #if span_USES_STD_SPAN
     std::cout << "(Presence of C++ language features not available: using std::span)\n";
 #else

test/span.t.cpp

@@ -228,11 +228,15 @@ CASE( "span<>: Allows to construct from two iterators" )
 CASE( "span<>: Allows to construct from two iterators - empty range" )
 {
 #if span_HAVE_ITERATOR_CTOR
+#if ! (span_COMPILER_MSVC_VER && defined(_DEBUG) )
     std::vector<int> v;
 
-    span<int> s( v.begin(), v.end() );
+   span<int> s( v.begin(), v.end() );
 
-    EXPECT( std::equal( s.begin(), s.end(), v.begin() ) );
+   EXPECT( std::equal( s.begin(), s.end(), v.begin() ) );
+#else
+    EXPECT( !!"construction from empty range not available (MSVC Debug)" );
+#endif
 #else
     EXPECT( !!"construction from iterator is not available (no C++11)" );
 #endif
@@ -254,11 +258,15 @@ CASE( "span<>: Allows to construct from an iterator and a size" )
 CASE( "span<>: Allows to construct from an iterator and a size - empty range" )
 {
 #if span_HAVE_ITERATOR_CTOR
+#if ! (span_COMPILER_MSVC_VER && defined(_DEBUG) )
     std::vector<int> v;
 
     span<int> s( v.begin(), v.size() );
 
     EXPECT( std::equal( s.begin(), s.end(), v.begin() ) );
+#else
+    EXPECT( !!"construction from empty range not available (MSVC Debug)" );
+#endif
 #else
     EXPECT( !!"construction from iterator is not available (no C++11)" );
 #endif