[libcxx-commits] [libcxx] [libcxx] adds ranges::fold_left_with_iter and ranges::fold_left (PR #75259)

[via libcxx-commits]

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+//===----------------------------------------------------------------------===//
+//
+// 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>;
----------------
EricWF wrote:

Rather than spending a bunch of time and effort on tests that only check compile time properties,
consider writing tests that actually run using the same types. It verifies all these tests do and more.

https://github.com/llvm/llvm-project/pull/75259