[memory.syn][specialized.algorithms] Prefer trailing returns on compl…

…ex signatures This proposed change follows the observation that when function template signatures get complicated, especially with long names for return types, and non-trivial requires clauses, it can be very hard to spot the function name and return type among the sea of tokens, in order to start mentally parsing the function. Here we propose using the trailing return type form of function declaration in those cases, and apply it consistently to the special algorithms in the '<memory>' header as a non-trivial sample size to gauge interest in a more complete PR that would cover the whole ranges library.
cplusplus · AlisdairM · May 7, 2024 · May 7, 2024 · 56fb956015314c0fc0aa6942556c0eafa4e74b0a
commit 56fb956015314c0fc0aa6942556c0eafa4e74b0a
diff --git a/source/algorithms.tex b/source/algorithms.tex
@@ -11105,10 +11105,10 @@
 namespace ranges {
   template<@\exposconcept{nothrow-forward-iterator}@ I, @\exposconcept{nothrow-sentinel-for}@<I> S>
     requires @\libconcept{default_initializable}@<iter_value_t<I>>
-    I uninitialized_default_construct(I first, S last);
+    auto uninitialized_default_construct(I first, S last) -> I;
   template<@\exposconcept{nothrow-forward-range}@ R>
     requires @\libconcept{default_initializable}@<range_value_t<R>>
-    borrowed_iterator_t<R> uninitialized_default_construct(R&& r);
+    auto uninitialized_default_construct(R&& r) -> borrowed_iterator_t<R>;
 }
 \end{itemdecl}
 
@@ -11126,7 +11126,8 @@
 \indexlibraryglobal{uninitialized_default_construct_n}%
 \begin{itemdecl}
 template<class NoThrowForwardIterator, class Size>
-  NoThrowForwardIterator uninitialized_default_construct_n(NoThrowForwardIterator first, Size n);
+  auto uninitialized_default_construct_n(NoThrowForwardIterator first, Size n)
+    -> NoThrowForwardIterator;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -11146,7 +11147,7 @@
 namespace ranges {
   template<@\exposconcept{nothrow-forward-iterator}@ I>
     requires @\libconcept{default_initializable}@<iter_value_t<I>>
-    I uninitialized_default_construct_n(I first, iter_difference_t<I> n);
+    auto uninitialized_default_construct_n(I first, iter_difference_t<I> n) -> I;
 }
 \end{itemdecl}
 
@@ -11184,10 +11185,10 @@
 namespace ranges {
   template<@\exposconcept{nothrow-forward-iterator}@ I, @\exposconcept{nothrow-sentinel-for}@<I> S>
     requires @\libconcept{default_initializable}@<iter_value_t<I>>
-    I uninitialized_value_construct(I first, S last);
+    auto uninitialized_value_construct(I first, S last) -> I;
   template<@\exposconcept{nothrow-forward-range}@ R>
     requires @\libconcept{default_initializable}@<range_value_t<R>>
-    borrowed_iterator_t<R> uninitialized_value_construct(R&& r);
+    auto uninitialized_value_construct(R&& r) -> borrowed_iterator_t<R>;
 }
 \end{itemdecl}
 
@@ -11205,7 +11206,8 @@
 \indexlibraryglobal{uninitialized_value_construct_n}%
 \begin{itemdecl}
 template<class NoThrowForwardIterator, class Size>
-  NoThrowForwardIterator uninitialized_value_construct_n(NoThrowForwardIterator first, Size n);
+  auto uninitialized_value_construct_n(NoThrowForwardIterator first, Size n)
+    -> NoThrowForwardIterator;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -11225,7 +11227,7 @@
 namespace ranges {
   template<@\exposconcept{nothrow-forward-iterator}@ I>
     requires @\libconcept{default_initializable}@<iter_value_t<I>>
-    I uninitialized_value_construct_n(I first, iter_difference_t<I> n);
+    auto uninitialized_value_construct_n(I first, iter_difference_t<I> n) -> I;
 }
 \end{itemdecl}
 
@@ -11244,8 +11246,8 @@
 \indexlibraryglobal{uninitialized_copy}%
 \begin{itemdecl}
 template<class InputIterator, class NoThrowForwardIterator>
-  NoThrowForwardIterator uninitialized_copy(InputIterator first, InputIterator last,
-                                            NoThrowForwardIterator result);
+  auto uninitialized_copy(InputIterator first, InputIterator last, NoThrowForwardIterator result)
+    -> NoThrowForwardIterator;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -11273,12 +11275,12 @@
   template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S1,
            @\exposconcept{nothrow-forward-iterator}@ O, @\exposconcept{nothrow-sentinel-for}@<O> S2>
     requires @\libconcept{constructible_from}@<iter_value_t<O>, iter_reference_t<I>>
-    uninitialized_copy_result<I, O>
-      uninitialized_copy(I ifirst, S1 ilast, O ofirst, S2 olast);
+    auto uninitialized_copy(I ifirst, S1 ilast, O ofirst, S2 olast)
+      -> uninitialized_copy_result<I, O>;
   template<@\libconcept{input_range}@ IR, @\exposconcept{nothrow-forward-range}@ OR>
     requires @\libconcept{constructible_from}@<range_value_t<OR>, range_reference_t<IR>>
-    uninitialized_copy_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>
-      uninitialized_copy(IR&& in_range, OR&& out_range);
+    auto uninitialized_copy(IR&& in_range, OR&& out_range);
+      -> uninitialized_copy_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>
 }
 \end{itemdecl}
 
@@ -11300,8 +11302,8 @@
 \indexlibraryglobal{uninitialized_copy_n}%
 \begin{itemdecl}
 template<class InputIterator, class Size, class NoThrowForwardIterator>
-  NoThrowForwardIterator uninitialized_copy_n(InputIterator first, Size n,
-                                              NoThrowForwardIterator result);
+  auto uninitialized_copy_n(InputIterator first, Size n, NoThrowForwardIterator result)
+    -> NoThrowForwardIterator;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -11328,8 +11330,8 @@
 namespace ranges {
   template<@\libconcept{input_iterator}@ I, @\exposconcept{nothrow-forward-iterator}@ O, @\exposconcept{nothrow-sentinel-for}@<O> S>
     requires @\libconcept{constructible_from}@<iter_value_t<O>, iter_reference_t<I>>
-    uninitialized_copy_n_result<I, O>
-      uninitialized_copy_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast);
+    auto uninitialized_copy_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast)
+      -> uninitialized_copy_n_result<I, O>;
 }
 \end{itemdecl}
 
@@ -11354,8 +11356,8 @@
 \indexlibraryglobal{uninitialized_move}%
 \begin{itemdecl}
 template<class InputIterator, class NoThrowForwardIterator>
-  NoThrowForwardIterator uninitialized_move(InputIterator first, InputIterator last,
-                                            NoThrowForwardIterator result);
+  auto uninitialized_move(InputIterator first, InputIterator last, NoThrowForwardIterator result)
+    -> NoThrowForwardIterator;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -11380,12 +11382,12 @@
   template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S1,
            @\exposconcept{nothrow-forward-iterator}@ O, @\exposconcept{nothrow-sentinel-for}@<O> S2>
     requires @\libconcept{constructible_from}@<iter_value_t<O>, iter_rvalue_reference_t<I>>
-    uninitialized_move_result<I, O>
-      uninitialized_move(I ifirst, S1 ilast, O ofirst, S2 olast);
+    auto uninitialized_move(I ifirst, S1 ilast, O ofirst, S2 olast)
+      -> uninitialized_move_result<I, O>;
   template<@\libconcept{input_range}@ IR, @\exposconcept{nothrow-forward-range}@ OR>
     requires @\libconcept{constructible_from}@<range_value_t<OR>, range_rvalue_reference_t<IR>>
-    uninitialized_move_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>
-      uninitialized_move(IR&& in_range, OR&& out_range);
+    auto uninitialized_move(IR&& in_range, OR&& out_range)
+      -> uninitialized_move_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>;
 }
 \end{itemdecl}
 
@@ -11414,8 +11416,8 @@
 \indexlibraryglobal{uninitialized_move_n}%
 \begin{itemdecl}
 template<class InputIterator, class Size, class NoThrowForwardIterator>
-  pair<InputIterator, NoThrowForwardIterator>
-    uninitialized_move_n(InputIterator first, Size n, NoThrowForwardIterator result);
+  auto uninitialized_move_n(InputIterator first, Size n, NoThrowForwardIterator result)
+    -> pair<InputIterator, NoThrowForwardIterator>;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -11439,8 +11441,8 @@
 namespace ranges {
   template<@\libconcept{input_iterator}@ I, @\exposconcept{nothrow-forward-iterator}@ O, @\exposconcept{nothrow-sentinel-for}@<O> S>
     requires @\libconcept{constructible_from}@<iter_value_t<O>, iter_rvalue_reference_t<I>>
-    uninitialized_move_n_result<I, O>
-      uninitialized_move_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast);
+    auto uninitialized_move_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast)
+      -> uninitialized_move_n_result<I, O>;
 }
 \end{itemdecl}
 
@@ -11490,10 +11492,10 @@
 namespace ranges {
   template<@\exposconcept{nothrow-forward-iterator}@ I, @\exposconcept{nothrow-sentinel-for}@<I> S, class T>
     requires @\libconcept{constructible_from}@<iter_value_t<I>, const T&>
-    I uninitialized_fill(I first, S last, const T& x);
+    auto uninitialized_fill(I first, S last, const T& x) -> I;
   template<@\exposconcept{nothrow-forward-range}@ R, class T>
     requires @\libconcept{constructible_from}@<range_value_t<R>, const T&>
-    borrowed_iterator_t<R> uninitialized_fill(R&& r, const T& x);
+    auto uninitialized_fill(R&& r, const T& x) -> borrowed_iterator_t<R>;
 }
 \end{itemdecl}
 
@@ -11511,7 +11513,8 @@
 \indexlibraryglobal{uninitialized_fill_n}%
 \begin{itemdecl}
 template<class NoThrowForwardIterator, class Size, class T>
-  NoThrowForwardIterator uninitialized_fill_n(NoThrowForwardIterator first, Size n, const T& x);
+  auto uninitialized_fill_n(NoThrowForwardIterator first, Size n, const T& x)
+    -> NoThrowForwardIterator;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -11531,7 +11534,7 @@
 namespace ranges {
   template<@\exposconcept{nothrow-forward-iterator}@ I, class T>
     requires @\libconcept{constructible_from}@<iter_value_t<I>, const T&>
-    I uninitialized_fill_n(I first, iter_difference_t<I> n, const T& x);
+    auto uninitialized_fill_n(I first, iter_difference_t<I> n, const T& x) -> I;
 }
 \end{itemdecl}
 
@@ -11615,10 +11618,10 @@
 namespace ranges {
   template<@\exposconcept{nothrow-input-iterator}@ I, @\exposconcept{nothrow-sentinel-for}@<I> S>
     requires @\libconcept{destructible}@<iter_value_t<I>>
-    constexpr I destroy(I first, S last) noexcept;
+    constexpr auto destroy(I first, S last) noexcept -> I;
   template<@\exposconcept{nothrow-input-range}@ R>
     requires @\libconcept{destructible}@<range_value_t<R>>
-    constexpr borrowed_iterator_t<R> destroy(R&& r) noexcept;
+    constexpr auto destroy(R&& r) -> borrowed_iterator_t<R> noexcept;
 }
 \end{itemdecl}
 
@@ -11655,7 +11658,7 @@
 namespace ranges {
   template<@\exposconcept{nothrow-input-iterator}@ I>
     requires @\libconcept{destructible}@<iter_value_t<I>>
-    constexpr I destroy_n(I first, iter_difference_t<I> n) noexcept;
+    constexpr auto destroy_n(I first, iter_difference_t<I> n) -> I noexcept;
 }
 \end{itemdecl}