DER: In visitor code, use ndnboost::any. We can use ndnboost::any because this is an internal header and will not conflict with the application if it uses boost::any.
diff --git a/include/ndnboost/any.hpp b/include/ndnboost/any.hpp
new file mode 100644
index 0000000..2419c6d
--- /dev/null
+++ b/include/ndnboost/any.hpp
@@ -0,0 +1,312 @@
+// See http://www.boost.org/libs/any for Documentation.
+
+#ifndef BOOST_ANY_INCLUDED
+#define BOOST_ANY_INCLUDED
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// what: variant type ndnboost::any
+// who: contributed by Kevlin Henney,
+// with features contributed and bugs found by
+// Antony Polukhin, Ed Brey, Mark Rodgers,
+// Peter Dimov, and James Curran
+// when: July 2001, Aplril 2013
+
+#include <algorithm>
+#include <typeinfo>
+
+#include "ndnboost/config.hpp"
+#include <ndnboost/type_traits/remove_reference.hpp>
+#include <ndnboost/type_traits/is_reference.hpp>
+#include <ndnboost/throw_exception.hpp>
+#include <ndnboost/static_assert.hpp>
+#include <ndnboost/utility/enable_if.hpp>
+#include <ndnboost/type_traits/is_same.hpp>
+
+// See boost/python/type_id.hpp
+// TODO: add BOOST_TYPEID_COMPARE_BY_NAME to config.hpp
+# if (defined(__GNUC__) && __GNUC__ >= 3) \
+ || defined(_AIX) \
+ || ( defined(__sgi) && defined(__host_mips)) \
+ || (defined(__hpux) && defined(__HP_aCC)) \
+ || (defined(linux) && defined(__INTEL_COMPILER) && defined(__ICC))
+# define BOOST_AUX_ANY_TYPE_ID_NAME
+#include <cstring>
+# endif
+
+namespace ndnboost
+{
+ class any
+ {
+ public: // structors
+
+ any() BOOST_NOEXCEPT
+ : content(0)
+ {
+ }
+
+ template<typename ValueType>
+ any(const ValueType & value)
+ : content(new holder<ValueType>(value))
+ {
+ }
+
+ any(const any & other)
+ : content(other.content ? other.content->clone() : 0)
+ {
+ }
+
+#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
+ // Move constructor
+ any(any&& other) BOOST_NOEXCEPT
+ : content(other.content)
+ {
+ other.content = 0;
+ }
+
+ // Perfect forwarding of ValueType
+ template<typename ValueType>
+ any(ValueType&& value, typename ndnboost::disable_if<ndnboost::is_same<any&, ValueType> >::type* = 0)
+ : content(new holder< typename remove_reference<ValueType>::type >(static_cast<ValueType&&>(value)))
+ {
+ }
+#endif
+
+ ~any() BOOST_NOEXCEPT
+ {
+ delete content;
+ }
+
+ public: // modifiers
+
+ any & swap(any & rhs) BOOST_NOEXCEPT
+ {
+ std::swap(content, rhs.content);
+ return *this;
+ }
+
+
+#ifdef BOOST_NO_CXX11_RVALUE_REFERENCES
+ template<typename ValueType>
+ any & operator=(const ValueType & rhs)
+ {
+ any(rhs).swap(*this);
+ return *this;
+ }
+
+ any & operator=(any rhs)
+ {
+ any(rhs).swap(*this);
+ return *this;
+ }
+
+#else
+ any & operator=(const any& rhs)
+ {
+ any(rhs).swap(*this);
+ return *this;
+ }
+
+ // move assignement
+ any & operator=(any&& rhs) BOOST_NOEXCEPT
+ {
+ rhs.swap(*this);
+ any().swap(rhs);
+ return *this;
+ }
+
+ // Perfect forwarding of ValueType
+ template <class ValueType>
+ any & operator=(ValueType&& rhs)
+ {
+ any(static_cast<ValueType&&>(rhs)).swap(*this);
+ return *this;
+ }
+#endif
+
+ public: // queries
+
+ bool empty() const BOOST_NOEXCEPT
+ {
+ return !content;
+ }
+
+ const std::type_info & type() const
+ {
+ return content ? content->type() : typeid(void);
+ }
+
+#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
+ private: // types
+#else
+ public: // types (public so any_cast can be non-friend)
+#endif
+
+ class placeholder
+ {
+ public: // structors
+
+ virtual ~placeholder()
+ {
+ }
+
+ public: // queries
+
+ virtual const std::type_info & type() const = 0;
+
+ virtual placeholder * clone() const = 0;
+
+ };
+
+ template<typename ValueType>
+ class holder : public placeholder
+ {
+ public: // structors
+
+ holder(const ValueType & value)
+ : held(value)
+ {
+ }
+
+#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
+ holder(ValueType&& value)
+ : held(static_cast< ValueType&& >(value))
+ {
+ }
+#endif
+ public: // queries
+
+ virtual const std::type_info & type() const
+ {
+ return typeid(ValueType);
+ }
+
+ virtual placeholder * clone() const
+ {
+ return new holder(held);
+ }
+
+ public: // representation
+
+ ValueType held;
+
+ private: // intentionally left unimplemented
+ holder & operator=(const holder &);
+ };
+
+#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
+
+ private: // representation
+
+ template<typename ValueType>
+ friend ValueType * any_cast(any *) BOOST_NOEXCEPT;
+
+ template<typename ValueType>
+ friend ValueType * unsafe_any_cast(any *) BOOST_NOEXCEPT;
+
+#else
+
+ public: // representation (public so any_cast can be non-friend)
+
+#endif
+
+ placeholder * content;
+
+ };
+
+ inline void swap(any & lhs, any & rhs) BOOST_NOEXCEPT
+ {
+ lhs.swap(rhs);
+ }
+
+ class bad_any_cast : public std::bad_cast
+ {
+ public:
+ virtual const char * what() const throw()
+ {
+ return "ndnboost::bad_any_cast: "
+ "failed conversion using ndnboost::any_cast";
+ }
+ };
+
+ template<typename ValueType>
+ ValueType * any_cast(any * operand) BOOST_NOEXCEPT
+ {
+ return operand &&
+#ifdef BOOST_AUX_ANY_TYPE_ID_NAME
+ std::strcmp(operand->type().name(), typeid(ValueType).name()) == 0
+#else
+ operand->type() == typeid(ValueType)
+#endif
+ ? &static_cast<any::holder<ValueType> *>(operand->content)->held
+ : 0;
+ }
+
+ template<typename ValueType>
+ inline const ValueType * any_cast(const any * operand) BOOST_NOEXCEPT
+ {
+ return any_cast<ValueType>(const_cast<any *>(operand));
+ }
+
+ template<typename ValueType>
+ ValueType any_cast(any & operand)
+ {
+ typedef BOOST_DEDUCED_TYPENAME remove_reference<ValueType>::type nonref;
+
+#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+ // If 'nonref' is still reference type, it means the user has not
+ // specialized 'remove_reference'.
+
+ // Please use BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION macro
+ // to generate specialization of remove_reference for your class
+ // See type traits library documentation for details
+ BOOST_STATIC_ASSERT(!is_reference<nonref>::value);
+#endif
+
+ nonref * result = any_cast<nonref>(&operand);
+ if(!result)
+ ndnboost::throw_exception(bad_any_cast());
+ return *result;
+ }
+
+ template<typename ValueType>
+ inline ValueType any_cast(const any & operand)
+ {
+ typedef BOOST_DEDUCED_TYPENAME remove_reference<ValueType>::type nonref;
+
+#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+ // The comment in the above version of 'any_cast' explains when this
+ // assert is fired and what to do.
+ BOOST_STATIC_ASSERT(!is_reference<nonref>::value);
+#endif
+
+ return any_cast<const nonref &>(const_cast<any &>(operand));
+ }
+
+ // Note: The "unsafe" versions of any_cast are not part of the
+ // public interface and may be removed at any time. They are
+ // required where we know what type is stored in the any and can't
+ // use typeid() comparison, e.g., when our types may travel across
+ // different shared libraries.
+ template<typename ValueType>
+ inline ValueType * unsafe_any_cast(any * operand) BOOST_NOEXCEPT
+ {
+ return &static_cast<any::holder<ValueType> *>(operand->content)->held;
+ }
+
+ template<typename ValueType>
+ inline const ValueType * unsafe_any_cast(const any * operand) BOOST_NOEXCEPT
+ {
+ return unsafe_any_cast<ValueType>(const_cast<any *>(operand));
+ }
+}
+
+// Copyright Kevlin Henney, 2000, 2001, 2002. All rights reserved.
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#endif