[libcxx-commits] [libcxx] [libc++][ranges] implement `std::ranges::zip_transform_view` (PR #79605)

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,97 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// constexpr decltype(auto) operator*() const noexcept(see below);
+
+#include <array>
+#include <cassert>
+#include <ranges>
+
+#include "../types.h"
+
+// Test noexcept
+// Remarks: Let Is be the pack 0, 1, ..., (sizeof...(Views)-1). The exception specification is equivalent to:
+//   noexcept(invoke(*parent_->fun_, *std::get<Is>(inner_.current_)...)).
+
+template <class ZipTransformView>
+concept DerefNoexcept = requires(std::ranges::iterator_t<ZipTransformView> iter) { requires noexcept(*iter); };
+
+struct ThrowingDerefIter {
+  using iterator_category = std::forward_iterator_tag;
+  using value_type        = int;
+  using difference_type   = std::intptr_t;
+
+  int operator*() const noexcept(false);
+
+  ThrowingDerefIter& operator++();
+  void operator++(int);
+
+  friend constexpr bool operator==(const ThrowingDerefIter&, const ThrowingDerefIter&) = default;
+};
+
+using NoexceptDerefIter = int*;
+
+template <bool NoExceptDeref>
+struct TestView : std::ranges::view_base {
+  using Iter = std::conditional_t<NoExceptDeref, NoexceptDerefIter, ThrowingDerefIter>;
+  Iter begin() const;
+  Iter end() const;
+};
+
+template <bool NoExceptCall>
+struct TestFn {
+  int operator()(auto&&...) const noexcept(NoExceptCall);
+};
+
+static_assert(DerefNoexcept<std::ranges::zip_transform_view<TestFn<true>, TestView<true>>>);
+static_assert(DerefNoexcept<std::ranges::zip_transform_view<TestFn<true>, TestView<true>, TestView<true>>>);
+static_assert(!DerefNoexcept<std::ranges::zip_transform_view<TestFn<true>, TestView<false>>>);
+static_assert(!DerefNoexcept<std::ranges::zip_transform_view<TestFn<false>, TestView<true>>>);
+static_assert(!DerefNoexcept<std::ranges::zip_transform_view<TestFn<false>, TestView<false>>>);
+static_assert(!DerefNoexcept<std::ranges::zip_transform_view<TestFn<false>, TestView<false>, TestView<true>>>);
+static_assert(!DerefNoexcept<std::ranges::zip_transform_view<TestFn<true>, TestView<false>, TestView<true>>>);
+static_assert(!DerefNoexcept<std::ranges::zip_transform_view<TestFn<false>, TestView<false>, TestView<false>>>);
+
+constexpr bool test() {
+  std::array a{1, 2, 3, 4};
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ldionne wrote:

I find this a bit light on the runtime testing. For example you could make sure that dereferencing an iterator twice within its lifetime works. And also maybe increment the iterator before dereferencing it again (in another test).

https://github.com/llvm/llvm-project/pull/79605