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Merge 2022-07 LWG Motion 17
P2322R6 ranges::fold
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‎source/algorithms.tex

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@@ -642,6 +642,9 @@
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template<class I>
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struct in_found_result;
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template<class I, class T>
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struct in_value_result;
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template<class O, class T>
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struct out_value_result;
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}
@@ -1215,6 +1218,91 @@
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@\libconcept{indirectly_comparable}@<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
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constexpr bool ends_with(R1&& r1, R2&& r2, Pred pred = {},
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Proj1 proj1 = {}, Proj2 proj2 = {});
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// \ref{alg.fold}, fold
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template<class F>
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class @\exposid{flipped}@ { // \expos
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F @\exposid{f}@; // \expos
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public:
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template<class T, class U> requires @\libconcept{invocable}@<F&, U, T>
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invoke_result_t<F&, U, T> operator()(T&&, U&&);
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};
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template<class F, class T, class I, class U>
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concept @\defexposconcept{indirectly-binary-left-foldable-impl}@ = // \expos
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@\libconcept{movable}@<T> && @\libconcept{movable}@<U> &&
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@\libconcept{convertible_to}@<T, U> && @\libconcept{invocable}@<F&, U, iter_reference_t<I>> &&
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@\libconcept{assignable_from}@<U&, invoke_result_t<F&, U, iter_reference_t<I>>>;
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template<class F, class T, class I>
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concept @\defexposconcept{indirectly-binary-left-foldable}@ = // \expos
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@\libconcept{copy_constructible}@<F> && @\libconcept{indirectly_readable}@<I> &&
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@\libconcept{invocable}@<F&, T, iter_reference_t<I>> &&
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@\libconcept{convertible_to}@<invoke_result_t<F&, T, iter_reference_t<I>>,
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decay_t<invoke_result_t<F&, T, iter_reference_t<I>>>> &&
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@\exposconcept{indirectly-binary-left-foldable-impl}@<F, T, I,
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decay_t<invoke_result_t<F&, T, iter_reference_t<I>>>>;
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template<class F, class T, class I>
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concept @\defexposconcept{indirectly-binary-right-foldable}@ = // \expos
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@\exposconcept{indirectly-binary-left-foldable}@<@\exposid{flipped}@<F>, T, I>;
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template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S, class T,
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@\exposconcept{indirectly-binary-left-foldable}@<T, I> F>
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constexpr auto fold_left(I first, S last, T init, F f);
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template<@\libconcept{input_range}@ R, class T, @\exposconcept{indirectly-binary-left-foldable}@<T, iterator_t<R>> F>
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constexpr auto fold_left(R&& r, T init, F f);
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template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S,
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@\exposconcept{indirectly-binary-left-foldable}@<iter_value_t<I>, I> F>
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requires @\libconcept{constructible_from}@<iter_value_t<I>, iter_reference_t<I>>
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constexpr auto fold_left_first(I first, S last, F f);
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template<@\libconcept{input_range}@ R, @\exposconcept{indirectly-binary-left-foldable}@<range_value_t<R>, iterator_t<R>> F>
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requires @\libconcept{constructible_from}@<range_value_t<R>, range_reference_t<R>>
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constexpr auto fold_left_first(R&& r, F f);
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template<@\libconcept{bidirectional_iterator}@ I, @\libconcept{sentinel_for}@<I> S, class T,
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@\exposconcept{indirectly-binary-right-foldable}@<T, I> F>
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constexpr auto fold_right(I first, S last, T init, F f);
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template<@\libconcept{bidirectional_range}@ R, class T,
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@\exposconcept{indirectly-binary-right-foldable}@<T, iterator_t<R>> F>
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constexpr auto fold_right(R&& r, T init, F f);
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template <@\libconcept{bidirectional_iterator}@ I, @\libconcept{sentinel_for}@<I> S,
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@\exposconcept{indirectly-binary-right-foldable}@<iter_value_t<I>, I> F>
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requires @\libconcept{constructible_from}@<iter_value_t<I>, iter_reference_t<I>>
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constexpr auto fold_right_last(I first, S last, F f);
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template<@\libconcept{bidirectional_range}@ R,
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@\exposconcept{indirectly-binary-right-foldable}@<range_value_t<R>, iterator_t<R>> F>
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requires @\libconcept{constructible_from}@<range_value_t<R>, range_reference_t<R>>
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constexpr auto fold_right_last(R&& r, F f);
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template<class I, class T>
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using fold_left_with_iter_result = in_value_result<I, T>;
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template<class I, class T>
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using fold_left_first_with_iter_result = in_value_result<I, T>;
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template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S, class T,
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@\exposconcept{indirectly-binary-left-foldable}@<T, I> F>
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constexpr @\seebelow@ fold_left_with_iter(I first, S last, T init, F f);
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template<@\libconcept{input_range}@ R, class T, @\exposconcept{indirectly-binary-left-foldable}@<T, iterator_t<R>> F>
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constexpr @\seebelow@ fold_left_with_iter(R&& r, T init, F f);
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template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S,
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@\exposconcept{indirectly-binary-left-foldable}@<iter_value_t<I>, I> F>
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requires @\libconcept{constructible_from}@<iter_value_t<I>, iter_reference_t<I>>
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constexpr @\seebelow@ fold_left_first_with_iter(I first, S last, F f);
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template<@\libconcept{input_range}@ R,
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@\exposconcept{indirectly-binary-left-foldable}@<range_value_t<R>, iterator_t<R>> F>
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requires @\libconcept{constructible_from}@<range_value_t<R>, range_reference_t<R>>
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constexpr @\seebelow@ fold_left_first_with_iter(R&& r, F f);
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}
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// \ref{alg.modifying.operations}, mutating sequence operations
@@ -3104,6 +3192,24 @@
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}
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};
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template<class I, class T>
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struct in_value_result {
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[[no_unique_address]] I in;
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[[no_unique_address]] T value;
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template<class I2, class T2>
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requires @\libconcept{convertible_to}@<const I&, I2> && @\libconcept{convertible_to}@<const T&, T2>
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constexpr operator in_value_result<I2, T2>() const & {
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return {in, value};
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}
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template<class I2, class T2>
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requires @\libconcept{convertible_to}@<I, I2> && @\libconcept{convertible_to}@<T, T2>
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constexpr operator in_value_result<I2, T2>() && {
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return {std::move(in), std::move(value)};
3210+
}
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};
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template<class O, class T>
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struct out_value_result {
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[[no_unique_address]] O out;
@@ -4518,6 +4624,170 @@
45184624
\end{codeblock}
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\end{itemdescr}
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\rSec2[alg.fold]{Fold}
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\indexlibraryglobal{fold_left}%
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\begin{itemdecl}
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template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S, class T, @\exposconcept{indirectly-binary-left-foldable}@<T, I> F>
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constexpr auto ranges::fold_left(I first, S last, T init, F f);
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template<@\libconcept{input_range}@ R, class T, @\exposconcept{indirectly-binary-left-foldable}@<T, iterator_t<R>> F>
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constexpr auto ranges::fold_left(R&& r, T init, F f);
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\end{itemdecl}
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\begin{itemdescr}
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\pnum
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\returns
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\begin{codeblock}
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ranges::fold_left_with_iter(std::move(first), last, std::move(init), f).value
4642+
\end{codeblock}
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\end{itemdescr}
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\indexlibraryglobal{fold_left_first}%
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\begin{itemdecl}
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template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S,
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@\exposconcept{indirectly-binary-left-foldable}@<iter_value_t<I>, I> F>
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requires @\libconcept{constructible_from}@<iter_value_t<I>, iter_reference_t<I>>
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constexpr auto ranges::fold_left_first(I first, S last, F f);
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template<@\libconcept{input_range}@ R, @\exposconcept{indirectly-binary-left-foldable}@<range_value_t<R>, iterator_t<R>> F>
4652+
requires @\libconcept{constructible_from}@<range_value_t<R>, range_reference_t<R>>
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constexpr auto ranges::fold_left_first(R&& r, F f);
4654+
\end{itemdecl}
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\begin{itemdescr}
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\pnum
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\returns
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\begin{codeblock}
4660+
ranges::fold_left_first_with_iter(std::move(first), last, f).value
4661+
\end{codeblock}
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\end{itemdescr}
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\indexlibraryglobal{fold_right}%
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\begin{itemdecl}
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template<@\libconcept{bidirectional_iterator}@ I, @\libconcept{sentinel_for}@<I> S, class T,
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@\exposconcept{indirectly-binary-right-foldable}@<T, I> F>
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constexpr auto ranges::fold_right(I first, S last, T init, F f);
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template<@\libconcept{bidirectional_range}@ R, class T,
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@\exposconcept{indirectly-binary-right-foldable}@<T, iterator_t<R>> F>
4671+
constexpr auto ranges::fold_right(R&& r, T init, F f);
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\end{itemdecl}
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\begin{itemdescr}
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\pnum
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\effects
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Equivalent to:
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\begin{codeblock}
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using U = decay_t<invoke_result_t<F&, iter_reference_t<I>, T>>;
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if (first == last)
4681+
return U(std::move(init));
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I tail = ranges::next(first, last);
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U accum = invoke(f, *--tail, std::move(init));
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while (first != tail)
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accum = invoke(f, *--tail, std::move(accum));
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return accum;
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\end{codeblock}
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\end{itemdescr}
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\indexlibraryglobal{fold_right_last}%
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\begin{itemdecl}
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template<@\libconcept{bidirectional_iterator}@ I, @\libconcept{sentinel_for}@<I> S,
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@\exposconcept{indirectly-binary-right-foldable}@<iter_value_t<I>, I> F>
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requires @\libconcept{constructible_from}@<iter_value_t<I>, iter_reference_t<I>>
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constexpr auto ranges::fold_right_last(I first, S last, F f);
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template<@\libconcept{bidirectional_range}@ R,
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@\exposconcept{indirectly-binary-right-foldable}@<range_value_t<R>, iterator_t<R>> F>
4698+
requires @\libconcept{constructible_from}@<range_value_t<R>, range_reference_t<R>>
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constexpr auto ranges::fold_right_last(R&& r, F f);
4700+
\end{itemdecl}
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4702+
\begin{itemdescr}
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\pnum
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Let \tcode{U} be
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\tcode{decltype(ranges::fold_right(first, last, iter_value_t<I>(*first), f))}.
4706+
4707+
\pnum
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\effects
4709+
Equivalent to:
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\begin{codeblock}
4711+
if (first == last)
4712+
return optional<U>();
4713+
I tail = ranges::prev(ranges::next(first, std::move(last)));
4714+
return optional<U>(in_place,
4715+
ranges::fold_right(std::move(first), tail, iter_value_t<I>(*tail), std::move(f)));
4716+
\end{codeblock}
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\end{itemdescr}
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4719+
\indexlibraryglobal{fold_left_with_iter}%
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\begin{itemdecl}
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template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S, class T,
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@\exposconcept{indirectly-binary-left-foldable}@<T, I> F>
4723+
constexpr @\seebelow@ ranges::fold_left_with_iter(I first, S last, T init, F f);
4724+
template<@\libconcept{input_range}@ R, class T, @\exposconcept{indirectly-binary-left-foldable}@<T, iterator_t<R>> F>
4725+
constexpr @\seebelow@ ranges::fold_left_with_iter(R&& r, T init, F f);
4726+
\end{itemdecl}
4727+
4728+
\begin{itemdescr}
4729+
\pnum
4730+
Let \tcode{U} be \tcode{decay_t<invoke_result_t<F\&, T, iter_reference_t<I>>>}.
4731+
4732+
\pnum
4733+
\effects
4734+
Equivalent to:
4735+
\begin{codeblock}
4736+
if (first == last)
4737+
return {std::move(first), U(std::move(init))};
4738+
U accum = invoke(f, std::move(init), *first);
4739+
for (++first; first != last; ++first)
4740+
accum = invoke(f, std::move(accum), *first);
4741+
return {std::move(first), std::move(accum)};
4742+
\end{codeblock}
4743+
4744+
\pnum
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\remarks
4746+
The return type is
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\tcode{fold_left_with_iter_result<I, U>} for the first overload and
4748+
\tcode{fold_left_with_iter_result<borrowed_iterator_t<R>, U>}
4749+
for the second overload.
4750+
\end{itemdescr}
4751+
4752+
\indexlibraryglobal{fold_left_first_with_iter}%
4753+
\begin{itemdecl}
4754+
template<@\libconcept{input_iterator}@ I, @\libconcept{sentinel_for}@<I> S,
4755+
@\exposconcept{indirectly-binary-left-foldable}@<iter_value_t<I>, I> F>
4756+
requires @\libconcept{constructible_from}@<iter_value_t<I>, iter_reference_t<I>>
4757+
constexpr @\seebelow@ ranges::fold_left_first_with_iter(I first, S last, F f);
4758+
template<@\libconcept{input_range}@ R, @\exposconcept{indirectly-binary-left-foldable}@<range_value_t<R>, iterator_t<R>> F>
4759+
requires @\libconcept{constructible_from}@<range_value_t<R>, range_reference_t<R>>
4760+
constexpr @\seebelow@ ranges::fold_left_first_with_iter(R&& r, F f);
4761+
\end{itemdecl}
4762+
4763+
\begin{itemdescr}
4764+
\pnum
4765+
Let \tcode{U} be
4766+
\begin{codeblock}
4767+
decltype(ranges::fold_left(std::move(first), last, iter_value_t<I>(*first), f))
4768+
\end{codeblock}
4769+
4770+
\pnum
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\effects
4772+
Equivalent to:
4773+
\begin{codeblock}
4774+
if (first == last)
4775+
return {std::move(first), optional<U>()};
4776+
optional<U> init(in_place, *first);
4777+
for (++first; first != last; ++first)
4778+
*init = invoke(f, std::move(*init), *first);
4779+
return {std::move(first), std::move(init)};
4780+
\end{codeblock}
4781+
4782+
\pnum
4783+
\remarks
4784+
The return type is
4785+
\tcode{fold_left_first_with_iter_result<I, optional<U>>}
4786+
for the first overload and
4787+
\tcode{fold_left_first_with_iter_result<borrowed_iterator_t<R>, optional<U>>}
4788+
for the second overload.
4789+
\end{itemdescr}
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\rSec1[alg.modifying.operations]{Mutating sequence operations}
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\rSec2[alg.copy]{Copy}

‎source/support.tex

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@@ -681,6 +681,7 @@
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#define @\defnlibxname{cpp_lib_ranges_chunk}@ 202202L // also in \libheader{ranges}
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#define @\defnlibxname{cpp_lib_ranges_chunk_by}@ 202202L // also in \libheader{ranges}
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#define @\defnlibxname{cpp_lib_ranges_contains}@ 202207L // also in \libheader{algorithm}
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#define @\defnlibxname{cpp_lib_ranges_fold}@ 202207L // also in \libheader{algorithm}
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#define @\defnlibxname{cpp_lib_ranges_iota}@ 202202L // also in \libheader{numeric}
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#define @\defnlibxname{cpp_lib_ranges_join_with}@ 202202L // also in \libheader{ranges}
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#define @\defnlibxname{cpp_lib_ranges_slide}@ 202202L // also in \libheader{ranges}

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