fix optional (assign not working) (#246)

Signed-off-by: turuslan <[email protected]>

Author: turuslan

include/libp2p/common/final_action.hpp

@@ -10,6 +10,8 @@
 #include <optional>
 #include <utility>
 
+#include <libp2p/common/option_take.hpp>
+
 namespace libp2p::common {
 
   template <typename F>
@@ -44,7 +46,7 @@ namespace libp2p::common {
   struct MovableFinalAction {
     MovableFinalAction() = delete;
     MovableFinalAction(MovableFinalAction &&func)
-        : func{std::exchange(func.func, {})} {}
+        : func{qtils::optionTake(func.func)} {}
     MovableFinalAction(const MovableFinalAction &func) = delete;
     MovableFinalAction &operator=(MovableFinalAction &&func) = delete;
     MovableFinalAction &operator=(const MovableFinalAction &func) = delete;

include/libp2p/common/option_take.hpp

@@ -0,0 +1,34 @@
+/**
+ * Copyright Quadrivium LLC
+ * All Rights Reserved
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <optional>
+
+// TODO(turuslan): qtils, https://github.com/qdrvm/kagome/issues/1813
+namespace qtils {
+  /**
+   * `std::move` doesn't reset `std::optional`.
+   * Typical bug:
+   *   std::optional<Fn> fn_once;
+   *   if (fn_once) {
+   *     // expected optional to be reset, but it wasn't
+   *     auto fn = std::move(fn_once);
+   *     fn();
+   *   }
+   *
+   * `std::exchange` or `std::swap` don't compile because `std::optional` can't
+   * be assigned.
+   *
+   * https://doc.rust-lang.org/std/option/enum.Option.html#method.take
+   */
+  template <typename T>
+  auto optionTake(std::optional<T> &optional) {
+    auto result = std::move(optional);
+    optional.reset();
+    return result;
+  }
+}  // namespace qtils