[range.adaptors] Extend the changes from P1456R1 to also apply to

take_while_view, drop_view, drop_while_view, and elements_view.

These are covered by the direction proposed in the paper, but were
inadvertently omitted from the list of things to change in the wording.

Author: zygoloid

papers/nxxxx.md

@@ -43,6 +43,26 @@ CWG motion 2: [P1234R5 "Paper name"](http://wg21.link/p1234r5), resolving 3 NB c
 
 ...
 
+### LWG motion 11
+
+The description of this paper specifies that:
+
+> each such `base()` member [of a range adaptor, that returns a copy of the underlying view]
+> be replaced to by two overloads:
+> a `const`-qualified overload that requires the type of the underlying view to model CopyConstructible, and
+> a `&&`-qualified overload that extracts the underlying view from the adaptor
+
+but the wording changes omitted explicit editing instructions
+to make these changes to the
+`take_while_view`, `drop_view`, `drop_while_view` and `elements_view`
+range adaptors, which were added by [P1035R7](http://wg21.link/p1035r7)
+(2019-07 LWG Motion 23), after R0 of this paper was authored.
+
+Consistent with the proposal in the paper,
+and after consulting the paper authors and the LWG chair,
+the corresponding changes were also applied to
+the additional range adaptors listed above.
+
 ## Disposition of editorial NB comments on C++ 2020 CD1
 
 Listed below are draft disposition for all comments that were

source/ranges.tex

@@ -4013,6 +4013,9 @@
 \rSec3[range.take.while.view]{Class template \tcode{take_while_view}}
 
 \indexlibraryglobal{take_while_view}%
+\indexlibrarymember{base}{take_while_view}%
+\indexlibrarymember{begin}{take_while_view}%
+\indexlibrarymember{end}{take_while_view}%
 \begin{codeblock}
 namespace std::ranges {
   template<view R, class Pred>
@@ -4028,7 +4031,9 @@
     take_while_view() = default;
     constexpr take_while_view(R base, Pred pred);
 
-    constexpr R base() const;
+    constexpr R base() const& requires copy_constructible<R> { return base_; }
+    constexpr R base() && { return std::move(base_); }
+
     constexpr const Pred& pred() const;
 
     constexpr auto begin() requires (!@\placeholder{simple-view}@<R>)
@@ -4061,17 +4066,6 @@
 \tcode{pred_} with \tcode{std::move(pred)}.
 \end{itemdescr}
 
-\indexlibrarymember{base}{take_while_view}%
-\begin{itemdecl}
-constexpr R base() const;
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\effects
-Equivalent to: \tcode{return base_;}
-\end{itemdescr}
-
 \indexlibrarymember{pred}{take_while_view}%
 \begin{itemdecl}
 constexpr const Pred& pred() const;
@@ -4177,6 +4171,9 @@
 \rSec3[range.drop.view]{Class template \tcode{drop_view}}
 
 \indexlibraryglobal{drop_view}%
+\indexlibrarymember{base}{drop_view}%
+\indexlibrarymember{end}{drop_view}%
+\indexlibrarymember{size}{drop_view}%
 \begin{codeblock}
 namespace std::ranges {
   template<view R>
@@ -4185,7 +4182,8 @@
     drop_view() = default;
     constexpr drop_view(R base, range_difference_t<R> count);
 
-    constexpr R base() const;
+    constexpr R base() const& requires copy_constructible<R> { return base_; }
+    constexpr R base() && { return std::move(base_); }
 
     constexpr auto begin()
       requires (!(@\placeholder{simple-view}@<R> && random_access_range<R>));
@@ -4241,17 +4239,6 @@
 \tcode{count_} with \tcode{count}.
 \end{itemdescr}
 
-\indexlibrarymember{base}{drop_view}%
-\begin{itemdecl}
-constexpr R base() const;
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\effects
-Equivalent to: \tcode{return base_;}
-\end{itemdescr}
-
 \indexlibrarymember{begin}{drop_view}%
 \begin{itemdecl}
 constexpr auto begin()
@@ -4311,6 +4298,8 @@
 \rSec3[range.drop.while.view]{Class template \tcode{drop_while_view}}
 
 \indexlibraryglobal{drop_while_view}%
+\indexlibrarymember{base}{drop_while_view}%
+\indexlibrarymember{end}{drop_while_view}%
 \begin{codeblock}
 namespace std::ranges {
   template<view R, class Pred>
@@ -4321,7 +4310,9 @@
     drop_while_view() = default;
     constexpr drop_while_view(R base, Pred pred);
 
-    constexpr R base() const;
+    constexpr R base() const& requires copy_constructible<R> { return base_; }
+    constexpr R base() && { return std::move(base_); }
+
     constexpr const Pred& pred() const;
 
     constexpr auto begin();
@@ -4351,17 +4342,6 @@
 \tcode{pred_} with \tcode{std::move(pred)}.
 \end{itemdescr}
 
-\indexlibrarymember{base}{drop_while_view}%
-\begin{itemdecl}
-constexpr R base() const;
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\effects
-Equivalent to: \tcode{return base_;}
-\end{itemdescr}
-
 \indexlibrarymember{pred}{drop_while_view}%
 \begin{itemdecl}
 constexpr const Pred& pred() const;
@@ -5992,6 +5972,10 @@
 \rSec3[range.elements.view]{Class template \tcode{elements_view}}
 
 \indexlibraryglobal{elements_view}%
+\indexlibrarymember{base}{elements_view}%
+\indexlibrarymember{begin}{elements_view}%
+\indexlibrarymember{end}{elements_view}%
+\indexlibrarymember{size}{elements_view}%
 \begin{codeblock}
 namespace std::ranges {
   template<class T, size_t N>
@@ -6012,7 +5996,8 @@
     elements_view() = default;
     constexpr explicit elements_view(R base);
 
-    constexpr R base() const;
+    constexpr R base() const& requires copy_constructible<R> { return base_; }
+    constexpr R base() && { return std::move(base_); }
 
     constexpr auto begin() requires (!@\placeholder{simple-view}@<R>)
     { return iterator<false>(ranges::begin(base_)); }
@@ -6050,17 +6035,6 @@
 Initializes \tcode{base_} with \tcode{std::move(base)}.
 \end{itemdescr}
 
-\indexlibrarymember{base}{elements_view}%
-\begin{itemdecl}
-constexpr R base() const;
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\effects
-Equivalent to: \tcode{return base_;}
-\end{itemdescr}
-
 \rSec3[range.elements.iterator]{Class template \tcode{elements_view::iterator}}
 
 \indexlibraryglobal{elements_view::iterator}%