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boost/proto/domain.hpp

///////////////////////////////////////////////////////////////////////////////
/// \file domain.hpp
/// Contains definition of domain\<\> class template and helpers for
/// defining domains with a generator and a grammar for controlling
/// operator overloading.
//
//  Copyright 2008 Eric Niebler. 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)

#ifndef BOOST_PROTO_DOMAIN_HPP_EAN_02_13_2007
#define BOOST_PROTO_DOMAIN_HPP_EAN_02_13_2007

#include <boost/proto/detail/prefix.hpp>
#include <boost/ref.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/proto/proto_fwd.hpp>
#include <boost/proto/generate.hpp>
#include <boost/proto/detail/suffix.hpp>

namespace boost { namespace proto
{

    namespace detail
    {
        struct not_a_generator
        {};

        struct not_a_grammar
        {};
    }

    BOOST_PROTO_BEGIN_ADL_NAMESPACE(domainns_)

    /// \brief For use in defining domain tags to be used
    /// with \c proto::extends\<\>. A \e Domain associates
    /// an expression type with a \e Generator, and optionally
    /// a \e Grammar.
    ///
    /// The Generator determines how new expressions in the
    /// domain are constructed. Typically, a generator wraps
    /// all new expressions in a wrapper that imparts
    /// domain-specific behaviors to expressions within its
    /// domain. (See \c proto::extends\<\>.)
    ///
    /// The Grammar determines whether a given expression is
    /// valid within the domain, and automatically disables
    /// any operator overloads which would cause an invalid
    /// expression to be created. By default, the Grammar
    /// parameter defaults to the wildcard, \c proto::_, which
    /// makes all expressions valid within the domain.
    ///
    /// Example:
    /// \code
    /// template<typename Expr>
    /// struct MyExpr;
    ///
    /// struct MyGrammar
    ///   : or_< terminal<_>, plus<MyGrammar, MyGrammar> >
    /// {};
    ///
    /// // Define MyDomain, in which all expressions are
    /// // wrapped in MyExpr<> and only expressions that
    /// // conform to MyGrammar are allowed.
    /// struct MyDomain
    ///   : domain<generator<MyExpr>, MyGrammar>
    /// {};
    ///
    /// // Use MyDomain to define MyExpr
    /// template<typename Expr>
    /// struct MyExpr
    ///   : extends<Expr, MyExpr<Expr>, MyDomain>
    /// {
    ///     // ...
    /// };
    /// \endcode
    ///
    template<
        typename Generator BOOST_PROTO_WHEN_BUILDING_DOCS(= default_generator)
      , typename Grammar   BOOST_PROTO_WHEN_BUILDING_DOCS(= proto::_)
    >
    struct domain
      : Generator
    {
        typedef Grammar proto_grammar;
        typedef void proto_is_domain_;
    };

    /// \brief The domain expressions have by default, if
    /// \c proto::extends\<\> has not been used to associate
    /// a domain with an expression.
    ///
    struct default_domain
      : domain<>
    {};

    /// \brief A pseudo-domain for use in functions and
    /// metafunctions that require a domain parameter. It
    /// indicates that the domain of the parent node should
    /// be inferred from the domains of the child nodes.
    ///
    /// \attention \c deduce_domain is not itself a valid domain.
    ///
    struct deduce_domain
      : domain<detail::not_a_generator, detail::not_a_grammar>
    {};

    BOOST_PROTO_END_ADL_NAMESPACE(domainns_)

    namespace result_of
    {
        /// A metafunction that returns \c mpl::true_
        /// if the type \c T is the type of a Proto domain;
        /// \c mpl::false_ otherwise. If \c T inherits from
        /// \c proto::domain\<\>, \c is_domain\<T\> is
        /// \c mpl::true_.
        template<typename T, typename Void  BOOST_PROTO_WHEN_BUILDING_DOCS(= void)>
        struct is_domain
          : mpl::false_
        {};

        /// INTERNAL ONLY
        ///
        template<typename T>
        struct is_domain<T, typename T::proto_is_domain_>
          : mpl::true_
        {};

        /// A metafunction that returns the domain of
        /// a given type. If \c T is a Proto expression
        /// type, it returns that expression's associated
        /// domain. If not, it returns
        /// \c proto::default_domain.
        template<typename T, typename Void  BOOST_PROTO_WHEN_BUILDING_DOCS(= void)>
        struct domain_of
        {
            typedef default_domain type;
        };

        /// INTERNAL ONLY
        ///
        template<typename T>
        struct domain_of<T, typename T::proto_is_expr_>
        {
            typedef typename T::proto_domain type;
        };

        /// INTERNAL ONLY
        ///
        template<typename T>
        struct domain_of<T &, void>
        {
            typedef typename domain_of<T>::type type;
        };

        /// INTERNAL ONLY
        ///
        template<typename T>
        struct domain_of<boost::reference_wrapper<T>, void>
        {
            typedef typename domain_of<T>::type type;
        };

        /// INTERNAL ONLY
        ///
        template<typename T>
        struct domain_of<boost::reference_wrapper<T> const, void>
        {
            typedef typename domain_of<T>::type type;
        };
    }
}}

#endif