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diff --git a/src/lib/dhcpsrv/key_from_key.h b/src/lib/dhcpsrv/key_from_key.h
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+// Copyright (C) 2013-2015 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef KEY_FROM_KEY_H
+#define KEY_FROM_KEY_H
+
+#include <functional>
+
+namespace isc {
+namespace dhcp {
+
+/// @brief Utility class which cascades two key extractors.
+///
+/// The key extractor (a.k.a. key extraction class) is used by the
+/// key-based indices to obtain the indexing keys from the elements of
+/// a multi_index_container. The standard key extractors can be used
+/// to retrieve indexing key values by accessing members or methods
+/// exposed by the elements (objects or structures) stored in a
+/// multi_index_container. For example, if a container holds objects
+/// of type A, then the public members of object A or its accessors can
+/// be used by the standard extractor classes such as "member" or
+/// "const_mem_fun" respectively. Assume more complex scenario, where
+/// multi_index_container holds objects of a type A, object A exposes
+/// its public member B, which in turn exposes the accessor function
+/// returning object C. One may want to use the value C (e.g. integer)
+/// to index objects A in the container. This can't be solved by using
+/// standard key extractors because object C is nested in B and thus
+/// it is not directly accessible from A. However, it is possible
+/// to specify two distinct key extractors, one used to extract value
+/// C from B, another one to extract value B from A. These two extractors
+/// can be then wrapped by another key extractor which can be used
+/// to obtain index key C from object A. This key extractor is implemented
+/// as a functor class. The functor calls functors specified as
+/// template parameters to retrieve the index value from the cascaded
+/// structure.
+///
+/// @tparam KeyExtractor1 extractor used to extract the key value from
+/// the object containing it.
+/// @tparam KeyExtractor2 extractor used to extract the nested object
+/// containing a key.
+template<typename KeyExtractor1, typename KeyExtractor2>
+class KeyFromKeyExtractor {
+public:
+    typedef typename KeyExtractor1::result_type result_type;
+
+    /// @brief Constructor.
+    KeyFromKeyExtractor()
+        : key1_(KeyExtractor1()), key2_(KeyExtractor2()) { };
+
+    /// @brief Extract key value from the object hierarchy.
+    ///
+    /// @param arg the key value.
+    ///
+    /// @tparam key value type.
+    template<typename T>
+    result_type operator() (T& arg) const {
+        return (key1_(key2_(arg)));
+    }
+private:
+    /// Key Extractor used to extract the key value from the
+    /// object containing it.
+    KeyExtractor1 key1_;
+    /// Key Extractor used to extract the nested object
+    /// containing a key.
+    KeyExtractor2 key2_;
+};
+
+} // end of isc::dhcp namespace
+} // end of isc namespace
+
+#endif // KEY_FROM_KEY_H