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diff --git a/stack_cleaner.cpp b/stack_cleaner.cpp
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+// Copyright 2011 Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+//   notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright
+//   notice, this list of conditions and the following disclaimer in the
+//   documentation and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors
+//   may be used to endorse or promote products derived from this software
+//   without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <cassert>
+#include <cstring>
+
+#include "stack_cleaner.hpp"
+#include "state.ipp"
+
+
+/// Internal implementation for lutok::stack_cleaner.
+struct lutok::stack_cleaner::impl {
+    /// Reference to the Lua state this stack_cleaner refers to.
+    state& state_ref;
+
+    /// The depth of the Lua stack to be restored.
+    unsigned int original_depth;
+
+    /// Constructor.
+    ///
+    /// \param state_ref_ Reference to the Lua state.
+    /// \param original_depth_ The depth of the Lua stack.
+    impl(state& state_ref_, const unsigned int original_depth_) :
+        state_ref(state_ref_),
+        original_depth(original_depth_)
+    {
+    }
+};
+
+
+/// Creates a new stack cleaner.
+///
+/// This gathers the current height of the stack so that extra elements can be
+/// popped during destruction.
+///
+/// \param state_ The Lua state.
+lutok::stack_cleaner::stack_cleaner(state& state_) :
+    _pimpl(new impl(state_, state_.get_top()))
+{
+}
+
+
+/// Pops any values from the stack not known at construction time.
+///
+/// \pre The current height of the stack must be equal or greater to the height
+/// of the stack when this object was instantiated.
+lutok::stack_cleaner::~stack_cleaner(void)
+{
+    const unsigned int current_depth = _pimpl->state_ref.get_top();
+    assert(current_depth >= _pimpl->original_depth);
+    const unsigned int diff = current_depth - _pimpl->original_depth;
+    if (diff > 0)
+        _pimpl->state_ref.pop(diff);
+}
+
+
+/// Forgets about any elements currently in the stack.
+///
+/// This allows a function to return values on the stack because all the
+/// elements that are currently in the stack will not be touched during
+/// destruction when the function is called.
+void
+lutok::stack_cleaner::forget(void)
+{
+    _pimpl->original_depth = _pimpl->state_ref.get_top();
+}