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

[via libcxx-commits]

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@@ -0,0 +1,100 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 TEST_SUPPORT_INVOCABLE_WITH_TELEMETRY_H
+#define TEST_SUPPORT_INVOCABLE_WITH_TELEMETRY_H
+
+#include <cassert>
+#include <concepts>
+#include <utility>
+
+#if TEST_STD_VER < 20
+#  error invocable_with_telemetry requires C++20
+#else
+template <class F>
+class invocable_with_telemetry {
+public:
+  invocable_with_telemetry() = default;
+
+  constexpr invocable_with_telemetry(F f, int& invocations, int& moves, int& copies)
+      : f_(f), invocations_(&invocations), moves_(&moves), copies_(&copies) {}
+
+  constexpr invocable_with_telemetry(invocable_with_telemetry&& other)
+    requires std::move_constructible<F>
+      : f_(std::move(other.f_)),
+        invocations_(assert(other.invocations_ != nullptr), std::exchange(other.invocations_, nullptr)),
+        moves_(assert(other.moves_ != nullptr), std::exchange(other.moves_, nullptr)),
+        copies_(assert(other.copies_ != nullptr), std::exchange(other.copies_, nullptr)) {
+    ++*moves_;
+  }
+
+  constexpr invocable_with_telemetry(invocable_with_telemetry const& other)
+    requires std::copy_constructible<F>
+      : f_(other.f_),
+        invocations_((assert(other.invocations_ != nullptr), other.invocations_)),
+        moves_((assert(other.moves_ != nullptr), other.moves_)),
+        copies_((assert(other.copies_ != nullptr), other.copies_)) {
+    ++*copies_;
+  }
+
+  constexpr invocable_with_telemetry& operator=(invocable_with_telemetry&& other)
+    requires std::movable<F>
+  {
+    // Not using move-and-swap idiom to ensure that copies and moves remain accurate.
+    assert(&other != this);
+    assert(other.invocations_ != nullptr);
+    assert(other.moves_ != nullptr);
+    assert(other.copies_ != nullptr);
+
+    f_           = std::move(other.f_);
+    invocations_ = std::exchange(other.invocations_, nullptr);
+    moves_       = std::exchange(other.moves_, nullptr);
+    copies_      = std::exchange(other.copies_, nullptr);
+
+    ++*moves_;
+    return *this;
+  }
+
+  constexpr invocable_with_telemetry& operator=(invocable_with_telemetry const& other)
+    requires std::copyable<F>
+  {
+    // Not using copy-and-swap idiom to ensure that copies and moves remain accurate.
+    assert(&other != this);
+    assert(other.invocations_ != nullptr);
+    assert(other.moves_ != nullptr);
+    assert(other.copies_ != nullptr);
+
+    f_           = other.f_;
+    invocations_ = other.invocations_;
+    moves_       = other.moves_;
+    copies_      = other.copies_;
+
+    ++*copies_;
+    return *this;
+  }
+
+  template <class... Args>
+    requires std::invocable<F&, Args...>
+  constexpr decltype(auto) operator()(Args&&... args) noexcept(std::is_nothrow_invocable_v<F&, Args...>) {
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EricWF wrote:

Does it mater if this is const-callable? 

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