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diff --git a/third_party/immer/immer/refcount/no_refcount_policy.hpp b/third_party/immer/immer/refcount/no_refcount_policy.hpp
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+++ b/third_party/immer/immer/refcount/no_refcount_policy.hpp
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+//
+// immer: immutable data structures for C++
+// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
+//
+// This software is distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
+//
+
+#pragma once
+
+namespace immer {
+
+struct disowned
+{};
+
+struct no_spinlock
+{
+    bool try_lock() { return true; }
+    void lock() {}
+    void unlock() {}
+
+    struct scoped_lock
+    {
+        scoped_lock(no_spinlock&) {}
+    };
+};
+
+/*!
+ * Disables reference counting, to be used with an alternative garbage
+ * collection strategy like a `gc_heap`.
+ */
+struct no_refcount_policy
+{
+    using spinlock_type = no_spinlock;
+
+    no_refcount_policy(){};
+    no_refcount_policy(disowned) {}
+
+    void inc() {}
+    bool dec() { return false; }
+    void dec_unsafe() {}
+    bool unique() { return false; }
+};
+
+} // namespace immer