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v8/include/cppgc/ephemeron-pair.h

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+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef INCLUDE_CPPGC_EPHEMERON_PAIR_H_
+#define INCLUDE_CPPGC_EPHEMERON_PAIR_H_
+
+#include "cppgc/liveness-broker.h"
+#include "cppgc/member.h"
+
+namespace cppgc {
+
+/**
+ * An ephemeron pair is used to conditionally retain an object.
+ * The `value` will be kept alive only if the `key` is alive.
+ */
+template <typename K, typename V>
+struct EphemeronPair {
+  EphemeronPair(K* k, V* v) : key(k), value(v) {}
+  WeakMember<K> key;
+  Member<V> value;
+
+  void ClearValueIfKeyIsDead(const LivenessBroker& broker) {
+    if (!broker.IsHeapObjectAlive(key)) value = nullptr;
+  }
+};
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_EPHEMERON_PAIR_H_