P3709R2 Reconsider parallel ranges::rotate_copy and ranges::reverse_copy

Author: eisenwave

source/algorithms.tex

@@ -2608,7 +2608,9 @@
 
   namespace ranges {
     template<class I, class O>
-      using reverse_copy_result = in_out_result<I, O>;
+      using @\libglobal{reverse_copy_result}@ = in_out_result<I, O>;
+    template<class I, class O>
+      using @\libglobal{reverse_copy_truncated_result}@ = in_in_out_result<I, I, O>;
 
     template<@\libconcept{bidirectional_iterator}@ I, @\libconcept{sentinel_for}@<I> S, @\libconcept{weakly_incrementable}@ O>
       requires @\libconcept{indirectly_copyable}@<I, O>
@@ -2622,12 +2624,12 @@
     template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
              @\libconcept{random_access_iterator}@ O, @\libconcept{sized_sentinel_for}@<O> OutS>
       requires @\libconcept{indirectly_copyable}@<I, O>
-      reverse_copy_result<I, O>
+      reverse_copy_truncated_result<I, O>
         reverse_copy(Ep&& exec, I first, S last, O result,
                      OutS result_last);                         // freestanding-deleted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, @\exposconcept{sized-random-access-range}@ OutR>
       requires @\libconcept{indirectly_copyable}@<iterator_t<R>, iterator_t<OutR>>
-      reverse_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
+      reverse_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
         reverse_copy(Ep&& exec, R&& r, OutR&& result_r);        // freestanding-deleted
   }
 
@@ -2671,7 +2673,9 @@
 
   namespace ranges {
     template<class I, class O>
-      using rotate_copy_result = in_out_result<I, O>;
+      using @\libglobal{rotate_copy_result}@ = in_out_result<I, O>;
+    template<class I, class O>
+      using @\libglobal{rotate_copy_truncated_result}@ = in_in_out_result<I, I, O>;
 
     template<@\libconcept{forward_iterator}@ I, @\libconcept{sentinel_for}@<I> S, @\libconcept{weakly_incrementable}@ O>
       requires @\libconcept{indirectly_copyable}@<I, O>
@@ -2686,12 +2690,12 @@
     template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
              @\libconcept{random_access_iterator}@ O, @\libconcept{sized_sentinel_for}@<O> OutS>
       requires @\libconcept{indirectly_copyable}@<I, O>
-      ranges::rotate_copy_result<I, O>
+      ranges::rotate_copy_truncated_result<I, O>
         ranges::rotate_copy(Ep&& exec, I first, I middle, S last, O result,
                             OutS result_last);                  // freestanding-deleted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, @\exposconcept{sized-random-access-range}@ OutR>
       requires @\libconcept{indirectly_copyable}@<iterator_t<R>, iterator_t<OutR>>
-      ranges::rotate_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
+      ranges::rotate_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
         ranges::rotate_copy(Ep&& exec, R&& r, iterator_t<R> middle,
                             OutR&& result_r);                   // freestanding-deleted
     // FIXME: once ranges:: is removed, reflow the previous two lines into one
@@ -8163,12 +8167,12 @@
 template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
          @\libconcept{random_access_iterator}@ O, @\libconcept{sized_sentinel_for}@<O> OutS>
   requires @\libconcept{indirectly_copyable}@<I, O>
-  ranges::reverse_copy_result<I, O>
+  ranges::reverse_copy_truncated_result<I, O>
     ranges::reverse_copy(Ep&& exec, I first, S last, O result,
                          OutS result_last);
 template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, @\exposconcept{sized-random-access-range}@ OutR>
   requires @\libconcept{indirectly_copyable}@<iterator_t<R>, iterator_t<OutR>>
-  ranges::reverse_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
+  ranges::reverse_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
     ranges::reverse_copy(Ep&& exec, R&& r, OutR&& result_r);
 \end{itemdecl}
 
@@ -8194,16 +8198,7 @@
 
 \pnum
 \returns
-\tcode{\{\exposid{NEW_FIRST}, result + $N$\}}.
-\begin{note}
-While the return type for the parallel and non-parallel algorithm overloads
-in the namespace \tcode{ranges} is the same,
-the semantics is different
-because for the parallel range algorithm overloads
-%FIXME: Comma.
-\tcode{result_last - result} can be insufficient
-to copy all data from the input.
-\end{note}
+\tcode{\{last, \exposid{NEW_FIRST}, result + $N$\}}.
 
 \pnum
 \complexity
@@ -8346,7 +8341,7 @@
 template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
          @\libconcept{random_access_iterator}@ O, @\libconcept{sized_sentinel_for}@<O> OutS>
   requires @\libconcept{indirectly_copyable}@<I, O>
-  ranges::rotate_copy_result<I, O>
+  ranges::rotate_copy_truncated_result<I, O>
     ranges::rotate_copy(Ep&& exec, I first, I middle, S last, O result, OutS result_last);
 \end{itemdecl}
 
@@ -8374,16 +8369,14 @@
 
 \pnum
 \returns
-\tcode{\{first + ($N$ + (middle - first)) \% $M$, result + $N$\}}.
-\begin{note}
-While the return type for the parallel and non-parallel algorithm overloads
-in the namespace \tcode{ranges} is the same,
-the semantics is different
-because for the parallel range algorithm overloads
-%FIXME: Comma.
-\tcode{result_last - result} can be insufficient
-to copy all data from the input.
-\end{note}
+\begin{itemize}
+\item
+  \tcode{\{middle + $N$, first, result + $N$\}}
+  if $N$ is less than \tcode{last - middle}.
+\item
+  Otherwise,
+  \tcode{\{last, first + ($N$ + (middle - first)) \% $M$, result + $N$\}}.
+\end{itemize}
 
 \pnum
 \complexity
@@ -8409,7 +8402,7 @@
 \begin{itemdecl}
 template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, @\exposconcept{sized-random-access-range}@ OutR>
   requires @\libconcept{indirectly_copyable}@<iterator_t<R>, iterator_t<OutR>>
-  ranges::rotate_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
+  ranges::rotate_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
     ranges::rotate_copy(Ep&& exec, R&& r, iterator_t<R> middle, OutR&& result_r);
 \end{itemdecl}