add operator+(int, iterator) overload (#30, #31, thanks @Crzyrndm)

Author: Crzyrndm

include/nonstd/ring_span.hpp

@@ -1104,6 +1104,12 @@ inline ring_iterator<RS,C> operator+( ring_iterator<RS,C> it, int i ) nsrs_noexc
     it += i; return it;
 }
 
+template< class RS, bool C >
+inline ring_iterator<RS,C> operator+(  int i, ring_iterator<RS,C> it ) nsrs_noexcept
+{
+    it += i; return it;
+}
+
 template< class RS, bool C >
 inline ring_iterator<RS,C> operator-( ring_iterator<RS,C> it, int i ) nsrs_noexcept
 {

test/ring-span.t.cpp

@@ -944,6 +944,7 @@ CASE( "ring_iterator: Allows to offset iterator (+)" " [extension]" )
     ring_span<int>::iterator pos = rs.begin();
 
     EXPECT( *(pos + 2) == arr[2] );
+    EXPECT( *(2 + pos) == arr[2] );
 #endif
 }