LWG3058 Parallel adjacent_difference shouldn't require creating temporaries

Author: jensmaurer

source/numerics.tex

@@ -9414,24 +9414,27 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{T} be the value type of \tcode{decltype(first)}.
+For the overloads that do not take an argument \tcode{binary_op},
+let \tcode{binary_op} be an lvalue
+that denotes an object of type \tcode{minus<>}.
+
 \pnum
 \requires
 \begin{itemize}
 \item
-For the overloads with no \tcode{ExecutionPolicy}, \tcode{InputIterator}'s value
-type shall be \tcode{MoveAssignable} (\tref{moveassignable}) and shall
+For the overloads with no \tcode{ExecutionPolicy},
+\tcode{T} shall be \tcode{MoveAssignable} (\tref{moveassignable}) and shall
 be constructible from the type of \tcode{*first}. \tcode{acc} (defined below)
 shall be writable\iref{iterator.requirements.general} to the \tcode{result}
-output iterator.  The result of the expression \tcode{val - std::move(acc)} or
+output iterator.  The result of the expression
 \tcode{binary_op(val, std::move(acc))} shall be writable to the \tcode{result} output iterator.
 
 \item
-For the overloads with an \tcode{ExecutionPolicy}, the value type of
-\tcode{ForwardIterator1}
-shall be \tcode{CopyConstructible} (\tref{copyconstructible}),
-constructible from the expression \tcode{*first - *first} or
-\tcode{binary_op(*first, *first)}, and assignable to the value type of
-\tcode{ForwardIterator2}.
+For the overloads with an \tcode{ExecutionPolicy},
+the result of the expressions \tcode{binary_op(*first, *first)} and
+\tcode{*first} shall be writable to \tcode{result}.
 
 \item
 For all overloads, in the ranges
@@ -9445,23 +9448,18 @@
 
 \pnum
 \effects For the overloads with no \tcode{ExecutionPolicy} and a non-empty range,
-the function creates an accumulator \tcode{acc} whose type is \tcode{InputIterator}'s
-value type, initializes it with \tcode{*first},
+the function creates an accumulator \tcode{acc} of type \tcode{T},
+initializes it with \tcode{*first},
 and assigns the result to \tcode{*result}. For every iterator \tcode{i} in \range{first + 1}{last}
-in order, creates an object \tcode{val} whose type is \tcode{InputIterator}'s value type, initializes it
-with \tcode{*i}, computes \tcode{val - std::move(acc)} or \tcode{binary_op(val, std::move(acc))}, assigns the result
+in order, creates an object \tcode{val} whose type is \tcode{T}, initializes it
+with \tcode{*i}, computes \tcode{binary_op(val, std::move(acc))}, assigns the result
 to \tcode{*(result + (i - first))}, and move assigns from \tcode{val} to \tcode{acc}.
 
 \pnum
-For the overloads with an \tcode{ExecutionPolicy} and a non-empty range, first the
-function creates an object whose type is \tcode{ForwardIterator1}'s value type,
-initializes it with \tcode{*first}, and assigns the result to \tcode{*result}.
-Then for every \tcode{d}
-in \crange{1}{last - first - 1}, creates an object \tcode{val} whose type is
-\tcode{ForwardIterator1}'s value type, initializes it with
-\tcode{*(first + d) - *(first + d - 1)} or
-\tcode{binary_op(*(first + d), *(first + d - 1))}, and assigns the result to
-\tcode{*(result + d)}.
+For the overloads with an \tcode{ExecutionPolicy} and a non-empty range,
+performs \tcode{*result = *first}.
+Then, for every \tcode{d} in \tcode{[1, last - first - 1]},
+performs \tcode{*(result + d) = binary_op(*(first + d), *(first + (d - 1)))}.
 
 \pnum
 \returns