Merge 2021-02 LWG Motion 6

Author: tkoeppe

source/ranges.tex

@@ -214,6 +214,9 @@
   // \ref{range.take}, take view
   template<@\libconcept{view}@> class take_view;
 
+  template<class T>
+    inline constexpr bool enable_borrowed_range<take_view<T>> = enable_borrowed_range<T>;
+
   namespace views { inline constexpr @\unspec@ take = @\unspec@; }
 
   // \ref{range.take.while}, take while view
@@ -228,6 +231,9 @@
   template<@\libconcept{view}@ V>
     class drop_view;
 
+  template<class T>
+    inline constexpr bool enable_borrowed_range<drop_view<T>> = enable_borrowed_range<T>;
+
   namespace views { inline constexpr @\unspec@ drop = @\unspec@; }
 
   // \ref{range.drop.while}, drop while view
@@ -236,6 +242,10 @@
              @\libconcept{indirect_unary_predicate}@<const Pred, iterator_t<V>>
     class drop_while_view;
 
+  template<class T, class Pred>
+    inline constexpr bool enable_borrowed_range<drop_while_view<T, Pred>> =
+      enable_borrowed_range<T>;
+
   namespace views { inline constexpr @\unspec@ drop_while = @\unspec@; }
 
   // \ref{range.join}, join view
@@ -267,20 +277,29 @@
     requires (!@\libconcept{common_range}@<V> && copyable<iterator_t<V>>)
   class common_view;
 
+  template<class T>
+    inline constexpr bool enable_borrowed_range<common_view<T>> = enable_borrowed_range<T>;
+
   namespace views { inline constexpr @\unspec@ common = @\unspec@; }
 
   // \ref{range.reverse}, reverse view
   template<@\libconcept{view}@ V>
     requires @\libconcept{bidirectional_range}@<V>
   class reverse_view;
 
+  template<class T>
+    inline constexpr bool enable_borrowed_range<reverse_view<T>> = enable_borrowed_range<T>;
+
   namespace views { inline constexpr @\unspec@ reverse = @\unspec@; }
 
   // \ref{range.elements}, elements view
   template<@\libconcept{input_range}@ V, size_t N>
     requires @\seebelow@
   class elements_view;
 
+  template<class T, size_t N>
+    inline constexpr bool enable_borrowed_range<elements_view<T, N>> = enable_borrowed_range<T>;
+
   template<class R>
     using keys_view = elements_view<views::all_t<R>, 0>;
   template<class R>