LWG3448 transform_view's sentinel<false> not comparable with iterator<true>

Author: burblebee

source/ranges.tex

@@ -160,6 +160,9 @@
 
   namespace views { inline constexpr @\unspec@ single = @\unspec@; }
 
+  template<bool Const, class T>
+    using @\exposid{maybe-const}@ = conditional_t<Const, const T, T>;   // \expos
+
   // \ref{range.iota}, iota view
   template<@\libconcept{weakly_incrementable}@ W, @\libconcept{semiregular}@ Bound = unreachable_sentinel_t>
     requires @\exposconcept{weakly-equality-comparable-with}@<W, Bound> && semiregular<W>
@@ -4168,14 +4171,19 @@
 
     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);
 
-    friend constexpr range_difference_t<@\exposid{Base}@>
-      operator-(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y)
-        requires @\libconcept{sized_sentinel_for}@<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
-    friend constexpr range_difference_t<@\exposid{Base}@>
-      operator-(const @\exposid{sentinel}@& y, const @\exposid{iterator}@<Const>& x)
-        requires @\libconcept{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{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{maybe-const}@<OtherConst, V>>
+      operator-(const @\exposid{sentinel}@& y, const @\exposid{iterator}@<OtherConst>& x);
   };
 }
 \end{codeblock}
@@ -4216,7 +4224,9 @@
 
 \indexlibrarymember{operator==}{transform_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}
@@ -4227,9 +4237,10 @@
 
 \indexlibrarymember{operator-}{transform_view::sentinel}%
 \begin{itemdecl}
-friend constexpr range_difference_t<@\exposid{Base}@>
-  operator-(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y)
-    requires @\libconcept{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{iterator}@<OtherConst>& x, const @\exposid{sentinel}@& y);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -4240,9 +4251,10 @@
 
 \indexlibrarymember{operator-}{transform_view::sentinel}%
 \begin{itemdecl}
-friend constexpr range_difference_t<@\exposid{Base}@>
-  operator-(const @\exposid{sentinel}@& y, const @\exposid{iterator}@<Const>& x)
-    requires @\libconcept{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}@& y, const @\exposid{iterator}@<OtherConst>& x);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -5346,7 +5358,9 @@
     constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> s)
       requires Const && @\libconcept{convertible_to}@<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;
 
-    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{codeblock}
@@ -5377,7 +5391,9 @@
 \indexlibrarymember{operator==}{join_view::sentinel}%3431
 
 \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}