[libcxx-commits] [libcxx] [libcxx] adds ranges::fold_left_with_iter and ranges::fold_left (PR #75259)
via libcxx-commits
libcxx-commits at lists.llvm.org
Tue Dec 12 16:19:29 PST 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Christopher Di Bella (cjdb)
<details>
<summary>Changes</summary>
This commit depends on #<!-- -->74672.
---
Patch is 47.49 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/75259.diff
17 Files Affected:
- (modified) libcxx/include/CMakeLists.txt (+1)
- (added) libcxx/include/__algorithm/fold.h (+118)
- (modified) libcxx/include/algorithm (+1)
- (modified) libcxx/include/module.modulemap.in (+1)
- (modified) libcxx/test/libcxx/diagnostics/ranges.nodiscard_extensions.verify.cpp (+13)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/requirements.compile.pass.cpp (+99)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/return_types.compile.pass.cpp (+171)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/valid.pass.cpp (+93)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left_with_iter/requirements.compile.pass.cpp (+107)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left_with_iter/return_types.compile.pass.cpp (+174)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left_with_iter/valid.pass.cpp (+116)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/gaussian_sum.h (+19)
- (added) libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/requirements.h (+82)
- (modified) libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.input/input_iterator.compile.pass.cpp (+1)
- (modified) libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp (+4)
- (modified) libcxx/test/std/ranges/range.adaptors/range.all/range.ref.view/borrowing.compile.pass.cpp (+1-1)
- (modified) libcxx/test/support/test_range.h (+28-26)
``````````diff
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index d8faf6467b79a..95702288a3c2f 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -22,6 +22,7 @@ set(files
__algorithm/find_first_of.h
__algorithm/find_if.h
__algorithm/find_if_not.h
+ __algorithm/fold.h
__algorithm/for_each.h
__algorithm/for_each_n.h
__algorithm/for_each_segment.h
diff --git a/libcxx/include/__algorithm/fold.h b/libcxx/include/__algorithm/fold.h
new file mode 100644
index 0000000000000..ad4e9820b479f
--- /dev/null
+++ b/libcxx/include/__algorithm/fold.h
@@ -0,0 +1,118 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_FOLD_H
+#define _LIBCPP___ALGORITHM_FOLD_H
+
+#include <__concepts/assignable.h>
+#include <__concepts/convertible_to.h>
+#include <__concepts/invocable.h>
+#include <__concepts/movable.h>
+#include <__config>
+#include <__functional/invoke.h>
+#include <__functional/reference_wrapper.h>
+#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__type_traits/decay.h>
+#include <__type_traits/invoke.h>
+#include <__utility/forward.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+namespace ranges {
+template <class _Ip, class _Tp>
+struct in_value_result {
+ _Ip in;
+ _Tp result;
+};
+
+template <class _Ip, class _Tp>
+using fold_left_with_iter_result = in_value_result<_Ip, _Tp>;
+
+template <class _Fp, class _Tp, class _Ip, class _Rp, class _Up = decay_t<_Rp>>
+concept __indirectly_binary_left_foldable_impl =
+ convertible_to<_Rp, _Up> && //
+ movable<_Tp> && //
+ movable<_Up> && //
+ convertible_to<_Tp, _Up> && //
+ invocable<_Fp&, _Up, iter_reference_t<_Ip>> && //
+ assignable_from<_Up&, invoke_result_t<_Fp&, _Up, iter_reference_t<_Ip>>>;
+
+template <class _Fp, class _Tp, class _Ip>
+concept __indirectly_binary_left_foldable =
+ copy_constructible<_Fp> && //
+ invocable<_Fp&, _Tp, iter_reference_t<_Ip>> && //
+ __indirectly_binary_left_foldable_impl<_Fp, _Tp, _Ip, invoke_result_t<_Fp&, _Tp, iter_reference_t<_Ip>>>;
+
+struct __fold_left_with_iter {
+ template <input_iterator _Ip, sentinel_for<_Ip> _Sp, class _Tp, __indirectly_binary_left_foldable<_Tp, _Ip> _Fp>
+ _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto
+ operator()(_Ip __first, _Sp __last, _Tp __init, _Fp __f) const {
+ using _Up = decay_t<invoke_result_t<_Fp&, _Tp, iter_reference_t<_Ip>>>;
+
+ if (__first == __last) {
+ return fold_left_with_iter_result<_Ip, _Up>{std::move(__first), _Up(std::move(__init))};
+ }
+
+ _Up __result = std::invoke(__f, std::move(__init), *__first);
+ for (++__first; __first != __last; ++__first) {
+ __result = std::invoke(__f, std::move(__result), *__first);
+ }
+
+ return fold_left_with_iter_result<_Ip, _Up>{std::move(__first), std::move(__result)};
+ }
+
+ template <input_range _Rp, class _Tp, __indirectly_binary_left_foldable<_Tp, iterator_t<_Rp>> _Fp>
+ _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Rp&& __r, _Tp __init, _Fp __f) const {
+ auto __result = (*this)(ranges::begin(__r), ranges::end(__r), std::move(__init), std::ref(__f));
+
+ using _Up = decay_t<invoke_result_t<_Fp&, _Tp, range_reference_t<_Rp>>>;
+ return fold_left_with_iter_result<borrowed_iterator_t<_Rp>, _Up>{
+ std::move(__result.in), std::move(__result.result)};
+ }
+};
+
+inline namespace __cpo {
+inline constexpr auto fold_left_with_iter = __fold_left_with_iter();
+} // namespace __cpo
+
+struct __fold_left {
+ template <input_iterator _Ip, sentinel_for<_Ip> _Sp, class _Tp, __indirectly_binary_left_foldable<_Tp, _Ip> _Fp>
+ _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto
+ operator()(_Ip __first, _Sp __last, _Tp __init, _Fp __f) const {
+ return fold_left_with_iter(std::move(__first), std::move(__last), std::move(__init), std::ref(__f)).result;
+ }
+
+ template <input_range _Rp, class _Tp, __indirectly_binary_left_foldable<_Tp, iterator_t<_Rp>> _Fp>
+ _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Rp&& __r, _Tp __init, _Fp __f) const {
+ return fold_left_with_iter(ranges::begin(__r), ranges::end(__r), std::move(__init), std::ref(__f)).result;
+ }
+};
+
+inline namespace __cpo {
+inline constexpr auto fold_left = __fold_left();
+} // namespace __cpo
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ALGORITHM_FOLD_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 627e7d20213fe..3fd9ba10f6310 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -1778,6 +1778,7 @@ template <class BidirectionalIterator, class Compare>
#include <__algorithm/find_first_of.h>
#include <__algorithm/find_if.h>
#include <__algorithm/find_if_not.h>
+#include <__algorithm/fold.h>
#include <__algorithm/for_each.h>
#include <__algorithm/for_each_n.h>
#include <__algorithm/generate.h>
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index 90ee7fbb2157c..359de41fdd128 100644
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -665,6 +665,7 @@ module std_private_algorithm_find_end [system
module std_private_algorithm_find_first_of [system] { header "__algorithm/find_first_of.h" }
module std_private_algorithm_find_if [system] { header "__algorithm/find_if.h" }
module std_private_algorithm_find_if_not [system] { header "__algorithm/find_if_not.h" }
+module std_private_algorithm_fold [system] { header "__algorithm/fold.h" }
module std_private_algorithm_for_each [system] { header "__algorithm/for_each.h" }
module std_private_algorithm_for_each_n [system] { header "__algorithm/for_each_n.h" }
module std_private_algorithm_for_each_segment [system] { header "__algorithm/for_each_segment.h" }
diff --git a/libcxx/test/libcxx/diagnostics/ranges.nodiscard_extensions.verify.cpp b/libcxx/test/libcxx/diagnostics/ranges.nodiscard_extensions.verify.cpp
index d11dcfcd0d2e4..f0a0e4889a760 100644
--- a/libcxx/test/libcxx/diagnostics/ranges.nodiscard_extensions.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/ranges.nodiscard_extensions.verify.cpp
@@ -12,6 +12,8 @@
#include <algorithm>
+#include "test_macros.h"
+
void test() {
int range[1];
int* iter = range;
@@ -87,4 +89,15 @@ void test() {
std::ranges::unique(iter, iter); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
std::ranges::upper_bound(range, 1); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
std::ranges::upper_bound(iter, iter, 1); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+#if TEST_STD_VER >= 23
+ std::ranges::fold_left(range, 0, std::plus());
+ // expected-warning at -1{{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::ranges::fold_left(iter, iter, 0, std::plus());
+ // expected-warning at -1{{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::ranges::fold_left_with_iter(range, 0, std::plus());
+ // expected-warning at -1{{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::ranges::fold_left_with_iter(iter, iter, 0, std::plus());
+ // expected-warning at -1{{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
}
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/requirements.compile.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/requirements.compile.pass.cpp
new file mode 100644
index 0000000000000..0b1c1e4eae1ea
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/requirements.compile.pass.cpp
@@ -0,0 +1,99 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// Checks that `std::ranges::fold_left`'s requirements are correct.
+
+#include <algorithm>
+#include <concepts>
+#include <functional>
+#include <iterator>
+#include <ranges>
+
+#include "test_iterators.h"
+#include "../requirements.h"
+
+// Covers indirectly_readable<I> too
+template <std::input_or_output_iterator T>
+ requires(!std::input_iterator<T>)
+void requires_input_iterator() {
+ static_assert(!requires(T t) { std::ranges::fold_left(t, std::unreachable_sentinel, 0, std::plus()); });
+}
+
+template <std::equality_comparable T>
+ requires(!std::sentinel_for<int*, T>)
+void requires_sentinel() {
+ static_assert(!requires(T first, T last) { std::ranges::fold_left(first, last, 0, std::plus()); });
+}
+
+template <class F>
+ requires(!std::copy_constructible<F>)
+void requires_copy_constructible_F() {
+ static_assert(!requires(int* first, int* last, F f) { std::ranges::fold_left(first, last, 0, std::move(f)); });
+}
+
+template <class F>
+ requires(!std::invocable<F&, int, std::iter_reference_t<int*>>)
+void requires_raw_invocable() {
+ static_assert(!requires(int* first, int* last, F f) { std::ranges::fold_left(first, last, 0, f); });
+}
+
+template <class F>
+ requires(!std::convertible_to<std::invoke_result_t<F&, S, std::iter_reference_t<S*>>,
+ std::decay_t<std::invoke_result_t<F&, S, std::iter_reference_t<S*>>>>)
+void requires_decaying_invoke_result() {
+ static_assert(!requires(S* first, S* last, S init, F f) { std::ranges::fold_left(first, last, init, f); });
+}
+
+template <class T>
+ requires(!std::movable<T>)
+void requires_movable_init() {
+ static_assert(!requires(copyable_non_movable* first, copyable_non_movable* last, T init) {
+ std::ranges::fold_left(first, last, init, std::plus());
+ });
+}
+
+template <class T>
+ requires(!std::movable<T>)
+void requires_movable_decayed() {
+ static_assert(!requires(T* first, T* last) { std::ranges::fold_left(first, last, 0, std::minus()); });
+}
+
+template <class T>
+ requires(!std::convertible_to<T, int>)
+void requires_init_is_convertible_to_decayed() {
+ static_assert(!requires(int* first, int* last, T init) { std::ranges::fold_left(first, last, init, std::plus()); });
+}
+
+template <class T>
+ requires(!std::invocable<std::plus<>&, T, T&>)
+void requires_invocable_with_decayed() {
+ static_assert(!requires(T* first, T* last, int init) { std::ranges::fold_left(first, last, init, std::plus()); });
+}
+
+template <class T>
+ requires(!std::assignable_from<T&, T volatile&>)
+void requires_assignable_from_invoke_result() {
+ static_assert(!requires(T* first, T* last, T init) { std::ranges::fold_left(first, last, init, std::plus()); });
+}
+
+void test() {
+ requires_input_iterator<bad_iterator_category>();
+ requires_sentinel<cpp17_input_iterator<int*>>();
+ requires_copy_constructible_F<non_copy_constructible_callable>();
+ requires_raw_invocable<not_invocable>();
+ requires_decaying_invoke_result<non_decayable_result>();
+ requires_movable_init<non_movable>();
+ requires_movable_decayed<copyable_non_movable>();
+ requires_init_is_convertible_to_decayed<not_convertible_to_int>();
+ requires_invocable_with_decayed<not_invocable_with_decayed>();
+ requires_assignable_from_invoke_result<not_assignable_to_decayed>();
+}
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/return_types.compile.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/return_types.compile.pass.cpp
new file mode 100644
index 0000000000000..911ce1615a1c7
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/return_types.compile.pass.cpp
@@ -0,0 +1,171 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// Checks that `std::ranges::fold_left`'s return type is correct.
+
+#include <algorithm>
+#include <concepts>
+#include <functional>
+#include <ranges>
+
+#include "test_iterators.h"
+#include "test_range.h"
+
+template <class Result, class T>
+concept is_T = std::same_as<Result, T>;
+
+using std::ranges::fold_left;
+[[maybe_unused]] auto f = [](int x, double y) { return x * y; };
+
+struct Int {
+ int value;
+};
+
+struct Long {
+ int value;
+
+ Long plus(Int) const;
+};
+
+namespace sentinel_based_ranges {
+template <class T>
+using cpp17_input_range = test_range<cpp17_input_iterator, T>;
+
+static_assert(requires(cpp17_input_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(cpp17_input_range<int> r) {
+ { fold_left(r, 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(cpp17_input_range<int> r) {
+ { fold_left(std::move(r), 0, std::plus()) } -> std::same_as<int>;
+});
+
+template <class T>
+using cpp20_input_range = test_range<cpp20_input_iterator, T>;
+
+static_assert(requires(cpp20_input_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(cpp20_input_range<int> r) {
+ { fold_left(r, 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(cpp20_input_range<int> r) {
+ { fold_left(std::move(r), 0, std::plus()) } -> std::same_as<int>;
+});
+
+template <class T>
+using forward_range = test_range<forward_iterator, T>;
+
+static_assert(requires(forward_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(forward_range<int> r) {
+ { fold_left(r, 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(forward_range<int> r) {
+ { fold_left(std::move(r), 0, std::plus()) } -> std::same_as<int>;
+});
+
+template <class T>
+using bidirectional_range = test_range<bidirectional_iterator, T>;
+
+static_assert(requires(bidirectional_range<short> r) {
+ { fold_left(r.begin(), r.end(), 0, f) } -> std::same_as<double>;
+});
+static_assert(requires(bidirectional_range<short> r) {
+ { fold_left(r, 0, f) } -> std::same_as<double>;
+});
+static_assert(requires(bidirectional_range<short> r) {
+ { fold_left(std::move(r), 0, f) } -> std::same_as<double>;
+});
+
+template <class T>
+using random_access_range = test_range<random_access_iterator, T>;
+
+static_assert(requires(random_access_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0, f) } -> std::same_as<double>;
+});
+static_assert(requires(random_access_range<int> r) {
+ { fold_left(r, 0, f) } -> std::same_as<double>;
+});
+static_assert(requires(random_access_range<int> r) {
+ { fold_left(std::move(r), 0, f) } -> std::same_as<double>;
+});
+
+template <class T>
+using contiguous_range = test_range<contiguous_iterator, T>;
+
+static_assert(requires(contiguous_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0.0f, std::plus()) } -> std::same_as<float>;
+});
+static_assert(requires(contiguous_range<int> r) {
+ { fold_left(r, 0.0f, std::plus()) } -> std::same_as<float>;
+});
+static_assert(requires(contiguous_range<int> r) {
+ { fold_left(std::move(r), 0.0f, std::plus()) } -> std::same_as<float>;
+});
+} // namespace sentinel_based_ranges
+
+namespace common_ranges {
+template <class T>
+using forward_range = test_common_range<forward_iterator, T>;
+
+static_assert(requires(forward_range<Int> r) {
+ { fold_left(r.begin(), r.end(), Long(0), &Long::plus) } -> std::same_as<Long>;
+});
+static_assert(requires(forward_range<Int> r) {
+ { fold_left(r, Long(0), &Long::plus) } -> std::same_as<Long>;
+});
+static_assert(requires(forward_range<Int> r) {
+ { fold_left(std::move(r), Long(0), &Long::plus) } -> std::same_as<Long>;
+});
+
+template <class T>
+using bidirectional_range = test_common_range<bidirectional_iterator, T>;
+
+static_assert(requires(bidirectional_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(bidirectional_range<int> r) {
+ { fold_left(r, 0, std::plus()) } -> std::same_as<int>;
+});
+static_assert(requires(bidirectional_range<int> r) {
+ { fold_left(std::move(r), 0, std::plus()) } -> std::same_as<int>;
+});
+
+template <class T>
+using random_access_range = test_common_range<random_access_iterator, T>;
+
+static_assert(requires(random_access_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0, f) } -> std::same_as<double>;
+});
+static_assert(requires(random_access_range<int> r) {
+ { fold_left(r, 0, f) } -> std::same_as<double>;
+});
+static_assert(requires(random_access_range<int> r) {
+ { fold_left(std::move(r), 0, f) } -> std::same_as<double>;
+});
+
+template <class T>
+using contiguous_range = test_common_range<contiguous_iterator, T>;
+
+static_assert(requires(contiguous_range<int> r) {
+ { fold_left(r.begin(), r.end(), 0.0f, std::plus()) } -> std::same_as<float>;
+});
+static_assert(requires(contiguous_range<int> r) {
+ { fold_left(r, 0.0f, std::plus()) } -> std::same_as<float>;
+});
+static_assert(requires(contiguous_range<int> r) {
+ { fold_left(std::move(r), 0.0f, std::plus()) } -> std::same_as<float>;
+});
+} // namespace common_ranges
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/valid.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/valid.pass.cpp
new file mode 100644
index 0000000000000..ef0fbb4b2a6d3
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/fold_left/valid.pass.cpp
@@ -0,0 +1,93 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// template<input_iterator I, sentinel_for<I> S, class T,
+// indirectly-binary-left-foldable<T, I> F>
+// constexpr see below ranges::fold_left(I first, S last, T init, F f);
+//
+// template<input_range R, class T, indirectly-binary-left-foldable<T, iterator_t<R>> F>
+// constexpr see below ranges::fold_left(R&& r, T init, F f);
+
+#include <algorithm>
+#include <cassert>
+#include <vector>
+#include <functional>
+
+#include "test_range.h"
+#include "../gaussian_sum.h"
+
+constexpr bool test() {
+ {
+ auto data = std::vector<int>{1, 2, 3, 4};
+ auto const result = std::ranges::fold_left(data.begin(), data.begin(), 0, std::plus());
+
+ assert(result == 0);
+
+ auto range = std::span(data.data(), 0);
+ assert(std::ranges::fold_left(range, 0, std::plus()) == result);
+ }
+ {
+ auto data = std::vector<int>{1, 2, 3, 4};
+ constexpr auto init = 100.1;
+ auto const result = std::ranges::fold_left(data.begin(), data.begin(), init, std::plus());
+
+ assert(result ==...
[truncated]
``````````
</details>
https://github.com/llvm/llvm-project/pull/75259
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