Chris@16: //  Copyright (c) 2001-2011 Joel de Guzman
Chris@16: //  Copyright (c) 2001-2011 Hartmut Kaiser
Chris@16: //
Chris@16: //  Distributed under the Boost Software License, Version 1.0. (See accompanying
Chris@16: //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #if !defined(SPIRIT_KARMA_OPTIONAL_MARCH_31_2007_0852AM)
Chris@16: #define SPIRIT_KARMA_OPTIONAL_MARCH_31_2007_0852AM
Chris@16: 
Chris@16: #if defined(_MSC_VER)
Chris@16: #pragma once
Chris@16: #endif
Chris@16: 
Chris@16: #include <boost/spirit/home/karma/domain.hpp>
Chris@16: #include <boost/spirit/home/karma/generator.hpp>
Chris@16: #include <boost/spirit/home/karma/meta_compiler.hpp>
Chris@16: #include <boost/spirit/home/support/info.hpp>
Chris@16: #include <boost/spirit/home/support/unused.hpp>
Chris@16: #include <boost/spirit/home/karma/detail/attributes.hpp>
Chris@16: #include <boost/spirit/home/support/container.hpp>
Chris@16: #include <boost/spirit/home/support/has_semantic_action.hpp>
Chris@16: #include <boost/spirit/home/support/handles_container.hpp>
Chris@16: #include <boost/mpl/assert.hpp>
Chris@16: #include <boost/optional.hpp>
Chris@16: #include <boost/type_traits/is_convertible.hpp>
Chris@16: 
Chris@16: namespace boost { namespace spirit
Chris@16: {
Chris@16:     ///////////////////////////////////////////////////////////////////////////
Chris@16:     // Enablers
Chris@16:     ///////////////////////////////////////////////////////////////////////////
Chris@16:     template <>
Chris@16:     struct use_operator<karma::domain, proto::tag::negate> // enables -g
Chris@16:       : mpl::true_ {};
Chris@16: 
Chris@16: }}
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: namespace boost { namespace spirit { namespace karma
Chris@16: {
Chris@16:     ///////////////////////////////////////////////////////////////////////////
Chris@16:     template <typename Subject>
Chris@16:     struct optional : unary_generator<optional<Subject> >
Chris@16:     {
Chris@16:         typedef Subject subject_type;
Chris@16:         typedef typename subject_type::properties properties;
Chris@16: 
Chris@16:         // Build a boost::optional from the subject's attribute. Note
Chris@16:         // that boost::optional may return unused_type if the
Chris@16:         // subject's attribute is an unused_type.
Chris@16:         template <typename Context, typename Iterator = unused_type>
Chris@16:         struct attribute
Chris@16:           : traits::build_optional<
Chris@16:                 typename traits::attribute_of<Subject, Context, Iterator>::type
Chris@16:             >
Chris@16:         {};
Chris@16: 
Chris@16:         optional(Subject const& subject)
Chris@16:           : subject(subject) {}
Chris@16: 
Chris@16:         template <
Chris@16:             typename OutputIterator, typename Context, typename Delimiter
Chris@16:           , typename Attribute>
Chris@16:         bool generate(OutputIterator& sink, Context& ctx
Chris@16:           , Delimiter const& d, Attribute const& attr) const
Chris@16:         {
Chris@16:             if (traits::has_optional_value(attr)) 
Chris@16:                 subject.generate(sink, ctx, d, traits::optional_value(attr));
Chris@16:             return sink_is_good(sink);
Chris@16:         }
Chris@16: 
Chris@16:         template <typename Context>
Chris@16:         info what(Context& context) const
Chris@16:         {
Chris@16:             return info("optional", subject.what(context));
Chris@16:         }
Chris@16: 
Chris@16:         Subject subject;
Chris@16:     };
Chris@16: 
Chris@16:     ///////////////////////////////////////////////////////////////////////////
Chris@16:     // Generator generators: make_xxx function (objects)
Chris@16:     ///////////////////////////////////////////////////////////////////////////
Chris@16:     template <typename Elements, typename Modifiers>
Chris@16:     struct make_composite<proto::tag::negate, Elements, Modifiers>
Chris@16:       : make_unary_composite<Elements, optional> {};
Chris@16: 
Chris@16: }}}
Chris@16: 
Chris@16: namespace boost { namespace spirit { namespace traits
Chris@16: {
Chris@16:     ///////////////////////////////////////////////////////////////////////////
Chris@16:     template <typename Subject>
Chris@16:     struct has_semantic_action<karma::optional<Subject> >
Chris@16:       : unary_has_semantic_action<Subject> {};
Chris@16: 
Chris@16:     ///////////////////////////////////////////////////////////////////////////
Chris@16:     template <typename Subject, typename Attribute, typename Context
Chris@16:       , typename Iterator>
Chris@16:     struct handles_container<karma::optional<Subject>, Attribute, Context
Chris@16:           , Iterator>
Chris@16:       : mpl::true_ {};
Chris@16: }}}
Chris@16: 
Chris@16: #endif