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

[Konstantin Varlamov via libcxx-commits]

================
@@ -0,0 +1,116 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_with_iter(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_with_iter(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 result = std::ranges::fold_left_with_iter(data.begin(), data.begin(), 0, std::plus());
+
+    assert(result.in == data.begin());
+    assert(result.result == 0);
+
+    auto range   = std::span(data.data(), 0);
+    auto rresult = std::ranges::fold_left_with_iter(range, 0, std::plus());
+
+    assert(rresult.in == result.in);
+    assert(rresult.result == result.result);
+  }
+  {
+    auto data           = std::vector<int>{1, 2, 3, 4};
+    constexpr auto init = 100.1;
+    auto result         = std::ranges::fold_left_with_iter(data.begin(), data.begin(), init, std::plus());
+
+    assert(result.in == data.begin());
+    assert(result.result == init);
+
+    auto range   = std::span(data.data(), 0);
+    auto rresult = std::ranges::fold_left_with_iter(range, init, std::plus());
+
+    assert(rresult.in == result.in);
+    assert(rresult.result == result.result);
+  }
+  {
+    auto data   = std::vector{1, 3, 5, 7, 9};
+    auto result = std::ranges::fold_left_with_iter(data.begin(), data.end(), 0, std::plus());
+
+    assert(result.in == data.end());
+    assert(result.result == gaussian_sum(data)); // sum of n ascending odd numbers = n^2
+
+    auto rresult = std::ranges::fold_left_with_iter(data, 0, std::plus());
+    assert(rresult.in == result.in);
+    assert(rresult.result == result.result);
+  }
+  {
+    auto data         = std::vector{2, 4, 6, 8, 10, 12};
+    auto const result = std::ranges::fold_left_with_iter(data.begin(), data.end(), 0L, std::plus<long>());
+
+    assert(result.in == data.end());
+    assert(result.result == gaussian_sum(data));
+
+    auto rresult = std::ranges::fold_left_with_iter(data, 0, std::plus());
+    assert(rresult.in == result.in);
+    assert(rresult.result == result.result);
+  }
+  {
+    auto data   = std::vector{-1.1, -2.2, -3.3, -4.4, -5.5, -6.6};
+    auto plus   = [](int const x, double const y) { return x + y; };
+    auto result = std::ranges::fold_left_with_iter(data.begin(), data.end(), 0.0, plus);
+
+    assert(result.in == data.end());
+    assert(result.result == -21.6); // int(  0.0) + -1.1 =   0 + -1.1 =  -1.1
+                                    // int(- 1.1) + -2.2 = - 1 + -2.2 =  -3.2
+                                    // int(- 3.2) + -3.3 = - 3 + -3.3 =  -6.3
+                                    // int(- 6.3) + -4.4 = - 6 + -4.4 = -10.4
+                                    // int(-10.4) + -5.5 = -10 + -5.5 = -15.5
+                                    // int(-15.5) + -6.6 = -15 + -6.6 = -21.6.
+
+    auto rresult = std::ranges::fold_left_with_iter(data, 0, plus);
+    assert(rresult.in == result.in);
+    assert(rresult.result == result.result);
+  }
+  {
+    auto data           = std::vector<double>{1.1, 2.1, 3.1, 4.1, 5.1, 6.1, 7.1, 8.1, 9.1};
+    auto plus           = [](double const x, double const y) { return static_cast<short>(x + y); };
+    constexpr auto init = 10.0;
+    auto result         = std::ranges::fold_left_with_iter(data.begin(), data.end(), init, plus);
+
+    assert(result.in == data.end());
+    assert(result.result == static_cast<short>(gaussian_sum(data) + init));
+
+    auto rresult = std::ranges::fold_left_with_iter(data, init, plus);
+    assert(rresult.in == result.in);
+    assert(rresult.result == result.result);
+  }
+
+  return true;
+}
+
+int main() {
----------------
var-const wrote:

Please add the parameters to `main` (we have some platforms that don't support `main()` with no arguments, weird as that sounds).

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