P2446R2 views::as_rvalue

Author: jensmaurer

source/ranges.tex

@@ -222,6 +222,16 @@
   template<class T>
     inline constexpr bool enable_borrowed_range<owning_view<T>> = enable_borrowed_range<T>;
 
+  // \ref{range.as.rvalue}, as rvalue view
+  template<@\libconcept{view}@ V>
+    requires @\libconcept{input_range}@<V>
+  class as_rvalue_view;
+
+  template<class T>
+    inline constexpr bool enable_borrowed_range<as_rvalue_view<T>> = enable_borrowed_range<T>;
+
+  namespace views { inline constexpr @\unspec@ as_rvalue = @\unspec@; }
+
   // \ref{range.filter}, filter view
   template<@\libconcept{input_range}@ V, @\libconcept{indirect_unary_predicate}@<iterator_t<V>> Pred>
     requires @\libconcept{view}@<V> && is_object_v<Pred>
@@ -3803,6 +3813,97 @@
 Initializes \exposid{r_} with \tcode{std::move(t)}.
 \end{itemdescr}
 
+\rSec2[range.as.rvalue]{As rvalue view}
+
+\rSec3[range.as.rvalue.overview]{Overview}
+
+\pnum
+\tcode{as_rvalue_view} presents a \libconcept{view} of an underlying sequence
+with the same behavior as the underlying sequence
+except that its elements are rvalues.
+Some generic algorithms can be called with a \tcode{as_rvalue_view}
+to replace copying with moving.
+
+\pnum
+\indexlibrarymember{as_rvalue}{views}%
+The name \tcode{views::as_rvalue} denotes
+a range adaptor object\iref{range.adaptor.object}.
+Let \tcode{E} be an expression and let \tcode{T} be \tcode{decltype((E))}.
+The expression \tcode{views::as_rvalue(E)} is expression-equivalent to:
+\begin{itemize}
+\item
+\tcode{views::all(E)} if \tcode{same_as<range_rvalue_reference_t<T>, range_reference_t<T>>} is \tcode{true}.
+\item
+Otherwise, \tcode{ranges::as_rvalue_view(E)}.
+\end{itemize}
+
+\pnum
+\begin{example}
+\begin{codeblock}
+vector<string> words = {"the", "quick", "brown", "fox", "ate", "a", "pterodactyl"};
+vector<string> new_words;
+ranges::copy(words | views::as_rvalue, back_inserter(new_words));
+  // moves each string from \tcode{words} into \tcode{new_words}
+\end{codeblock}
+\end{example}
+
+\rSec3[range.as.rvalue.view]{Class template \tcode{as_rvalue_view}}
+
+\begin{codeblock}
+namespace std::ranges {
+  template<@\libconcept{input_range}@ V>
+    requires @\libconcept{view}@<V>
+  class @\libglobal{as_rvalue_view}@ : public view_interface<as_rvalue_view<V>>
+  {
+    V @\exposid{base_}@ = V();      // \expos
+
+  public:
+    as_rvalue_view() requires @\libconcept{default_initializable}@<V> = default;
+    constexpr explicit as_rvalue_view(V base);
+
+    constexpr V base() const & requires copy_constructible<V> { return @\exposid{base_}@; }
+    constexpr V base() && { return std::move(@\exposid{base_}@); }
+
+    constexpr auto begin() requires (!@\exposconcept{simple-view}@<V>)
+      { return move_iterator(ranges::begin(@\exposid{base_}@)); }
+    constexpr auto begin() const requires @\libconcept{range}@<const V>
+      { return move_iterator(ranges::begin(@\exposid{base_}@)); }
+
+    constexpr auto end() requires (!@\exposconcept{simple-view}@<V>) {
+      if constexpr (@\libconcept{common_range}@<V>) {
+        return move_iterator(ranges::end(@\exposid{base_}@));
+      } else {
+        return move_sentinel(ranges::end(@\exposid{base_}@));
+      }
+    }
+    constexpr auto end() const requires @\libconcept{range}@<const V> {
+      if constexpr (@\libconcept{common_range}@<const V>) {
+        return move_iterator(ranges::end(@\exposid{base_}@));
+      } else {
+        return move_sentinel(ranges::end(@\exposid{base_}@));
+      }
+    }
+
+    constexpr auto size() requires @\libconcept{sized_range}@<V> { return ranges::size(@\exposid{base_}@); }
+    constexpr auto size() const requires @\libconcept{sized_range}@<const V> { return ranges::size(@\exposid{base_}@); }
+  };
+
+  template<class R>
+    as_rvalue_view(R&&) -> as_rvalue_view<views::all_t<R>>;
+}
+\end{codeblock}
+
+\indexlibraryctor{as_rvalue_view}%
+\begin{itemdecl}
+constexpr explicit as_rvalue_view(V base);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Initializes \exposid{base_} with \tcode{std::move(base)}.
+\end{itemdescr}
+
 \rSec2[range.filter]{Filter view}
 
 \rSec3[range.filter.overview]{Overview}

source/support.tex

@@ -671,6 +671,7 @@
 #define @\defnlibxname{cpp_lib_quoted_string_io}@                  201304L // also in \libheader{iomanip}
 #define @\defnlibxname{cpp_lib_ranges}@                            202202L
   // also in \libheader{algorithm}, \libheader{functional}, \libheader{iterator}, \libheader{memory}, \libheader{ranges}
+#define @\defnlibxname{cpp_lib_ranges_as_rvalue}@                  202207L // also in \libheader{ranges}
 #define @\defnlibxname{cpp_lib_ranges_chunk}@                      202202L // also in \libheader{ranges}
 #define @\defnlibxname{cpp_lib_ranges_chunk_by}@                   202202L // also in \libheader{ranges}
 #define @\defnlibxname{cpp_lib_ranges_iota}@                       202202L // also in \libheader{numeric}