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+/*=============================================================================
+    Copyright (c) 1998-2003 Joel de Guzman
+    http://spirit.sourceforge.net/
+
+  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)
+=============================================================================*/
+#if !defined(BOOST_SPIRIT_RULE_HPP)
+#define BOOST_SPIRIT_RULE_HPP
+
+#include <boost/static_assert.hpp>
+
+///////////////////////////////////////////////////////////////////////////////
+//
+//  Spirit predefined maximum number of simultaneously usable different
+//  scanner types.
+//
+//  This limit defines the maximum number of possible different scanner
+//  types for which a specific rule<> may be used. If this isn't defined, a
+//  rule<> may be used with one scanner type only (multiple scanner support
+//  is disabled).
+//
+///////////////////////////////////////////////////////////////////////////////
+#if !defined(BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT)
+#  define BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT 1
+#endif
+
+//  Ensure a meaningful maximum number of simultaneously usable scanner types
+BOOST_STATIC_ASSERT(BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT > 0);
+
+#include <boost/scoped_ptr.hpp>
+#include <boost/spirit/home/classic/namespace.hpp>
+#include <boost/spirit/home/classic/core/non_terminal/impl/rule.ipp>
+
+#if BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT > 1
+#  include <boost/preprocessor/enum_params.hpp>
+#endif
+
+///////////////////////////////////////////////////////////////////////////////
+namespace boost { namespace spirit {
+
+BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN
+
+#if BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT > 1
+
+    ///////////////////////////////////////////////////////////////////////////
+    //
+    //  scanner_list (a fake scanner)
+    //
+    //      Typically, rules are tied to a specific scanner type and
+    //      a particular rule cannot be used with anything else. Sometimes
+    //      there's a need for rules that can accept more than one scanner
+    //      type. The scanner_list<S0, ...SN> can be used as a template
+    //      parameter to the rule class to specify up to the number of
+    //      scanner types defined by the BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT
+    //      constant. Example:
+    //
+    //          rule<scanner_list<ScannerT0, ScannerT1> > r;
+    //
+    //      *** This feature is available only to compilers that support
+    //      partial template specialization. ***
+    //
+    ///////////////////////////////////////////////////////////////////////////
+    template <
+        BOOST_PP_ENUM_PARAMS(
+            BOOST_SPIRIT_RULE_SCANNERTYPE_LIMIT,
+            typename ScannerT
+        )
+    >
+    struct scanner_list : scanner_base {};
+
+#endif
+
+    ///////////////////////////////////////////////////////////////////////////
+    //
+    //  rule class
+    //
+    //      The rule is a polymorphic parser that acts as a named place-
+    //      holder capturing the behavior of an EBNF expression assigned to
+    //      it.
+    //
+    //      The rule is a template class parameterized by:
+    //
+    //          1) scanner (scanner_t, see scanner.hpp),
+    //          2) the rule's context (context_t, see parser_context.hpp)
+    //          3) an arbitrary tag (tag_t, see parser_id.hpp) that allows
+    //             a rule to be tagged for identification.
+    //
+    //      These template parameters may be specified in any order. The
+    //      scanner will default to scanner<> when it is not specified.
+    //      The context will default to parser_context when not specified.
+    //      The tag will default to parser_address_tag when not specified.
+    //
+    //      The definition of the rule (its right hand side, RHS) held by
+    //      the rule through a scoped_ptr. When a rule is seen in the RHS
+    //      of an assignment or copy construction EBNF expression, the rule
+    //      is held by the LHS rule by reference.
+    //
+    ///////////////////////////////////////////////////////////////////////////
+    template <
+        typename T0 = nil_t
+      , typename T1 = nil_t
+      , typename T2 = nil_t
+    >
+    class rule
+        : public impl::rule_base<
+            rule<T0, T1, T2>
+          , rule<T0, T1, T2> const&
+          , T0, T1, T2>
+    {
+    public:
+
+        typedef rule<T0, T1, T2> self_t;
+        typedef impl::rule_base<
+            self_t
+          , self_t const&
+          , T0, T1, T2>
+        base_t;
+
+        typedef typename base_t::scanner_t scanner_t;
+        typedef typename base_t::attr_t attr_t;
+        typedef impl::abstract_parser<scanner_t, attr_t> abstract_parser_t;
+
+        rule() : ptr() {}
+        ~rule() {}
+
+        rule(rule const& r)
+        : ptr(new impl::concrete_parser<rule, scanner_t, attr_t>(r)) {}
+
+        template <typename ParserT>
+        rule(ParserT const& p)
+        : ptr(new impl::concrete_parser<ParserT, scanner_t, attr_t>(p)) {}
+
+        template <typename ParserT>
+        rule& operator=(ParserT const& p)
+        {
+            ptr.reset(new impl::concrete_parser<ParserT, scanner_t, attr_t>(p));
+            return *this;
+        }
+
+        rule& operator=(rule const& r)
+        {
+            ptr.reset(new impl::concrete_parser<rule, scanner_t, attr_t>(r));
+            return *this;
+        }
+
+        rule<T0, T1, T2>
+        copy() const
+        {
+            return rule<T0, T1, T2>(ptr.get() ? ptr->clone() : 0);
+        }
+
+    private:
+        friend class impl::rule_base_access;
+
+        abstract_parser_t*
+        get() const
+        {
+            return ptr.get();
+        }
+
+        rule(abstract_parser_t* ptr_)
+        : ptr(ptr_) {}
+
+        rule(abstract_parser_t const* ptr_)
+        : ptr(ptr_) {}
+
+        scoped_ptr<abstract_parser_t> ptr;
+    };
+
+BOOST_SPIRIT_CLASSIC_NAMESPACE_END
+
+}} // namespace BOOST_SPIRIT_CLASSIC_NS
+
+#endif