LWG3406 elements_view::begin() and elements_view::end() have incompatible constraints

Author: burblebee

source/ranges.tex

@@ -6294,13 +6294,13 @@
     constexpr auto begin() requires (!@\exposconcept{simple-view}@<V>)
     { return @\exposid{iterator}@<false>(ranges::begin(@\exposid{base_}@)); }
 
-    constexpr auto begin() const requires @\exposconcept{simple-view}@<V>
+    constexpr auto begin() const requires @\libconcept{range}@<const V>
     { return @\exposid{iterator}@<true>(ranges::begin(@\exposid{base_}@)); }
 
-    constexpr auto end()
+    constexpr auto end() requires (!@\exposconcept{simple-view}@<V> && !common_range<V>)
     { return @\exposid{sentinel}@<false>{ranges::end(@\exposid{base_}@)}; }
 
-    constexpr auto end() requires common_range<V>
+    constexpr auto end() requires (!@\exposconcept{simple-view}@<V> && common_range<V>)
     { return @\exposid{iterator}@<false>{ranges::end(@\exposid{base_}@)}; }
 
     constexpr auto end() const requires range<const V>
@@ -6700,15 +6700,19 @@
 
     constexpr sentinel_t<@\exposid{Base}@> base() const;
 
-    friend constexpr bool operator==(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y);
+    template<bool OtherConst>
+      requires @\libconcept{sentinel_for}@<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{maybe-const}@<OtherConst, V>>>
+    friend constexpr bool operator==(const @\exposid{iterator}@<OtherConst>& x, const @\exposid{sentinel}@& y);
 
+    template<bool OtherConst>
+      requires @\libconcept{sized_sentinel_for}@<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{maybe-const}@<OtherConst, V>>>
     friend constexpr range_difference_t<@\exposid{Base}@>
-      operator-(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y)
-        requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
+      operator-(const @\exposid{iterator}@<OtherConst>& x, const @\exposid{sentinel}@& y);
 
-    friend constexpr range_difference_t<@\exposid{Base}@>
-      operator-(const @\exposid{sentinel}@& x, const @\exposid{iterator}@<Const>& y)
-        requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
+    template<bool OtherConst>
+      requires @\libconcept{sized_sentinel_for}@<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{maybe-const}@<OtherConst, V>>>
+    friend constexpr range_difference_t<@\exposid{maybe-const}@<OtherConst, V>>
+      operator-(const @\exposid{sentinel}@& x, const @\exposid{iterator}@<OtherConst>& y);
   };
 }
 \end{codeblock}
@@ -6749,7 +6753,9 @@
 
 \indexlibrarymember{operator==}{elements_view::sentinel}%
 \begin{itemdecl}
-friend constexpr bool operator==(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y);
+template<bool OtherConst>
+  requires @\libconcept{sentinel_for}@<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{maybe-const}@<OtherConst, V>>>
+friend constexpr bool operator==(const @\exposid{iterator}@<OtherConst>& x, const @\exposid{sentinel}@& y);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -6760,9 +6766,10 @@
 
 \indexlibrarymember{operator-}{elements_view::sentinel}%
 \begin{itemdecl}
+template<bool OtherConst>
+  requires @\libconcept{sized_sentinel_for}@<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{maybe-const}@<OtherConst, V>>>
 friend constexpr range_difference_t<@\exposid{Base}@>
-  operator-(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y)
-    requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
+  operator-(const @\exposid{iterator}@<OtherConst>& x, const @\exposid{sentinel}@& y);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -6773,9 +6780,10 @@
 
 \indexlibrarymember{operator-}{elements_view::sentinel}%
 \begin{itemdecl}
-friend constexpr range_difference_t<@\exposid{Base}@>
-  operator-(const @\exposid{sentinel}@& x, const @\exposid{iterator}@<Const>& y)
-    requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
+template<bool OtherConst>
+  requires @\libconcept{sized_sentinel_for}@<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{maybe-const}@<OtherConst, V>>>
+friend constexpr range_difference_t<@\exposid{maybe-const}@<OtherConst, V>>
+  operator-(const @\exposid{sentinel}@& x, const @\exposid{iterator}@<OtherConst>& y);
 \end{itemdecl}
 
 \begin{itemdescr}