visitor.hh

/* vim: set sw=4 sts=4 et foldmethod=syntax : */
 
/*
 * Copyright (c) 2008, 2009, 2010, 2011, 2013 Ciaran McCreesh
 *
 * This file is part of the Paludis package manager. Paludis is free software;
 * you can redistribute it and/or modify it under the terms of the GNU General
 * Public License version 2, as published by the Free Software Foundation.
 *
 * Paludis is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place, Suite 330, Boston, MA  02111-1307  USA
 */
 
#ifndef PALUDIS_GUARD_PALUDIS_UTIL_VISITOR_HH
#define PALUDIS_GUARD_PALUDIS_UTIL_VISITOR_HH 1
 
#include <paludis/util/attributes.hh>
#include <paludis/util/visitor-fwd.hh>
#include <paludis/util/no_type.hh>
#include <functional>
 
namespace paludis
{
    /**
     * Used by accept_visitor.
     *
     * \nosubgrouping
     * \ingroup g_visitors
     */
    template <typename Visitor_>
    class PALUDIS_VISIBLE AcceptVisitor
    {
        private:
            Visitor_ & _v;
 
        public:
            typedef void result_type;
 
            ///\name Visitor operations
            ///\{
 
            AcceptVisitor(Visitor_ & v) :
                _v(v)
            {
            }
 
            template <typename T_>
            void operator() (T_ & t) const
            {
                t.accept(_v);
            }
 
            ///\}
    };
 
    /**
     * Used by accept_visitor.
     *
     * \nosubgrouping
     * \ingroup g_visitors
     */
    template <typename Visitor_, typename Returning_>
    class PALUDIS_VISIBLE AcceptVisitorReturning
    {
        private:
            Visitor_ & _v;
 
        public:
            typedef Returning_ result_type;
 
            ///\name Visitor operations
            ///\{
 
            AcceptVisitorReturning(Visitor_ & v) :
                _v(v)
            {
            }
 
            template <typename T_>
            Returning_ operator() (T_ & t) const
            {
                return t.template accept_returning<Returning_>(_v);
            }
 
            ///\}
    };
 
    /**
     * Convenience function for using a visitor with a standard algorithm.
     *
     * \ingroup g_visitors
     */
    template <typename Visitor_>
    AcceptVisitor<Visitor_> PALUDIS_VISIBLE accept_visitor(Visitor_ & v)
    {
        return AcceptVisitor<Visitor_>(v);
    }
 
    /**
     * Convenience function for using a visitor with a standard algorithm.
     *
     * \ingroup g_visitors
     */
    template <typename Returning_, typename Visitor_>
    AcceptVisitorReturning<Visitor_, Returning_> PALUDIS_VISIBLE accept_visitor_returning(Visitor_ & v)
    {
        return AcceptVisitorReturning<Visitor_, Returning_>(v);
    }
 
    template <typename>
    struct ExtractFirstArgumentType;
 
    template <typename T_, typename R_, typename A1_, typename... As_>
    struct ExtractFirstArgumentType<R_ (T_::*) (A1_, As_...) const>
    {
        typedef A1_ Type;
    };
 
    template <typename T_>
    using FirstCallArgumentType = typename ExtractFirstArgumentType<decltype(&T_::operator())>::Type;
 
    template <typename>
    struct ExtractResultType;
 
    template <typename T_, typename R_, typename... As_>
    struct ExtractResultType<R_ (T_::*) (As_...) const>
    {
        typedef R_ Type;
    };
 
    template <typename T_>
    using CallResultType = typename std::remove_const<typename ExtractResultType<decltype(&T_::operator())>::Type>::type;
 
    template <typename Revisitor_, typename Result_, typename... Cases_>
    struct MadeVisitor;
 
    template <typename Revisitor_, typename Result_>
    struct MadeVisitor<Revisitor_, Result_>
    {
        Result_ visit(const NoType<0u> &) const;
    };
 
    template <typename>
    struct CallThisCaseNeedsTwoArgs;
 
    template <typename T_, typename R_, typename A1_>
    struct CallThisCaseNeedsTwoArgs<R_ (T_::*) (A1_) const>
    {
        enum { value = false };
    };
 
    template <typename T_, typename R_, typename A1_, typename A2_>
    struct CallThisCaseNeedsTwoArgs<R_ (T_::*) (A1_, A2_) const>
    {
        enum { value = true };
    };
 
    template <typename Result_, typename Case_, typename V_, bool needs_two_args_>
    struct CallThisCase;
 
    template <typename Result_, typename Case_, typename V_>
    struct CallThisCase<Result_, Case_, V_, false>
    {
        static Result_ call(const Case_ & thiscase, const FirstCallArgumentType<Case_> & v, const V_ &)
        {
            return thiscase(v);
        }
    };
 
    template <typename Result_, typename Case_, typename V_>
    struct CallThisCase<Result_, Case_, V_, true>
    {
        static Result_ call(const Case_ & thiscase, const FirstCallArgumentType<Case_> & v, const V_ & revisitor)
        {
            return thiscase(v, accept_visitor_returning<Result_>(revisitor));
        }
    };
 
    template <typename Case_, typename V_>
    struct CallThisCase<void, Case_, V_, true>
    {
        static void call(const Case_ & thiscase, const FirstCallArgumentType<Case_> & v, const V_ & revisitor)
        {
            thiscase(v, accept_visitor(revisitor));
        }
    };
 
    template <typename Revisitor_, typename Result_, typename Case_, typename... Rest_>
    struct MadeVisitor<Revisitor_, Result_, Case_, Rest_...> :
        MadeVisitor<Revisitor_, Result_, Rest_...>
    {
        const Case_ & thiscase;
 
        MadeVisitor(const Case_ & c, const Rest_ & ... cases) :
            MadeVisitor<Revisitor_, Result_, Rest_...>(cases...),
            thiscase(c)
        {
        }
 
        using MadeVisitor<Revisitor_, Result_, Rest_...>::visit;
 
        Result_ visit(const FirstCallArgumentType<Case_> & v) const
        {
            return CallThisCase<Result_, Case_, Revisitor_, CallThisCaseNeedsTwoArgs<decltype(&Case_::operator())>::value>::call(
                    thiscase, v, *static_cast<const Revisitor_ *>(this));
        }
    };
 
    template <typename Result_, typename... Cases_>
    struct BaseMadeVisitor :
        MadeVisitor<BaseMadeVisitor<Result_, Cases_...>, Result_, Cases_...>
    {
        BaseMadeVisitor(const Cases_ & ... cases) :
            MadeVisitor<BaseMadeVisitor<Result_, Cases_...>, Result_, Cases_...>(cases...)
        {
        }
    };
 
    template <typename Case_, typename... Cases_>
    auto make_visitor(const Case_ & firstcase, const Cases_ & ... cases) -> BaseMadeVisitor<CallResultType<Case_>, Case_, Cases_...>
    {
        return BaseMadeVisitor<CallResultType<Case_>, Case_, Cases_...>{ firstcase, cases... };
    }
 
    template <typename Result_, typename Base_>
    using Revisit = std::function<Result_ (const Base_ &)>;
 
    template <>
    class DeclareAbstractVisitMethods<TypeListTail>
    {
        public:
            void forward_visit(const NoType<0u> &);
    };
 
    template <typename TypeList_>
    class DeclareAbstractVisitMethods :
        public virtual DeclareAbstractVisitMethods<typename TypeList_::Tail>
    {
        public:
            using DeclareAbstractVisitMethods<typename TypeList_::Tail>::forward_visit;
 
            virtual void forward_visit(typename TypeList_::Item &) = 0;
    };
 
    template <typename TypeList_>
    class WrappedVisitorBase :
        public virtual DeclareAbstractVisitMethods<TypeList_>
    {
    };
 
    template <typename RealClass_>
    class ImplementVisitMethods<RealClass_, TypeListTail>
    {
        public:
            void forward_visit(const NoType<1u> &);
    };
 
    template <typename RealClass_, typename TypeList_>
    class ImplementVisitMethods :
        public virtual DeclareAbstractVisitMethods<TypeList_>,
        public ImplementVisitMethods<RealClass_, typename TypeList_::Tail>
    {
        public:
            using ImplementVisitMethods<RealClass_, typename TypeList_::Tail>::forward_visit;
 
            void forward_visit(typename TypeList_::Item & n) override
            {
                static_cast<RealClass_ *>(this)->perform_visit(n);
            }
    };
 
    template <typename TypeList_, typename UnwrappedVisitor_>
    class WrappedVoidResultVisitor :
        public WrappedVisitorBase<TypeList_>,
        public ImplementVisitMethods<WrappedVoidResultVisitor<TypeList_, UnwrappedVisitor_>, TypeList_>
    {
        private:
            UnwrappedVisitor_ & _unwrapped_visitor;
 
        public:
            WrappedVoidResultVisitor(UnwrappedVisitor_ & v) :
                _unwrapped_visitor(v)
            {
            }
 
            template <typename C_>
            void perform_visit(C_ & t)
            {
                _unwrapped_visitor.visit(t);
            }
    };
 
    template <typename TypeList_, typename Result_, typename UnwrappedVisitor_>
    class WrappedNonVoidResultVisitor :
            public WrappedVisitorBase<TypeList_>,
            public ImplementVisitMethods<WrappedNonVoidResultVisitor<TypeList_, Result_, UnwrappedVisitor_>,
                TypeList_>
    {
        private:
            UnwrappedVisitor_ & _unwrapped_visitor;
 
        public:
            Result_ result;
 
            WrappedNonVoidResultVisitor(UnwrappedVisitor_ & v, const Result_ & r) :
                _unwrapped_visitor(v),
                result(r)
            {
            }
 
            template <typename C_>
            void perform_visit(C_ & t)
            {
                result = _unwrapped_visitor.visit(t);
            }
    };
 
    template <typename BaseClass_, typename VisitableTypeList_>
    class DeclareAbstractAcceptMethods
    {
        private:
            virtual void _real_accept(WrappedVisitorBase<VisitableTypeList_> &) = 0;
            virtual void _real_accept_const(WrappedVisitorBase<typename MakeTypeListConst<VisitableTypeList_>::Type> &) const = 0;
 
        public:
            typedef VisitableTypeList_ VisitableTypeList;
            typedef BaseClass_ VisitableBaseClass;
 
            template <typename UnwrappedVisitor_>
            void accept(UnwrappedVisitor_ & v)
            {
                WrappedVoidResultVisitor<VisitableTypeList_, UnwrappedVisitor_> vv(v);
                _real_accept(vv);
            }
 
            template <typename UnwrappedVisitor_>
            void accept(UnwrappedVisitor_ & v) const
            {
                WrappedVoidResultVisitor<typename MakeTypeListConst<VisitableTypeList_>::Type, UnwrappedVisitor_> vv(v);
                _real_accept_const(vv);
            }
 
            template <typename UnwrappedVisitor_>
            void accept(const UnwrappedVisitor_ & v)
            {
                WrappedVoidResultVisitor<VisitableTypeList_, const UnwrappedVisitor_> vv(v);
                _real_accept(vv);
            }
 
            template <typename UnwrappedVisitor_>
            void accept(const UnwrappedVisitor_ & v) const
            {
                WrappedVoidResultVisitor<typename MakeTypeListConst<VisitableTypeList_>::Type, const UnwrappedVisitor_> vv(v);
                _real_accept_const(vv);
            }
 
            template <typename Result_, typename UnwrappedVisitor_>
            Result_ accept_returning(UnwrappedVisitor_ & v, const Result_ & r = Result_())
            {
                WrappedNonVoidResultVisitor<VisitableTypeList_, Result_, UnwrappedVisitor_> vv(v, r);
                _real_accept(vv);
                return vv.result;
            }
 
            template <typename Result_, typename UnwrappedVisitor_>
            Result_ accept_returning(const UnwrappedVisitor_ & v, const Result_ & r = Result_())
            {
                WrappedNonVoidResultVisitor<VisitableTypeList_, Result_, const UnwrappedVisitor_> vv(v, r);
                _real_accept(vv);
                return vv.result;
            }
 
            template <typename Result_, typename UnwrappedVisitor_>
            Result_ accept_returning(UnwrappedVisitor_ & v, const Result_ & r = Result_()) const
            {
                WrappedNonVoidResultVisitor<typename MakeTypeListConst<VisitableTypeList_>::Type, Result_, UnwrappedVisitor_> vv(v, r);
                _real_accept_const(vv);
                return vv.result;
            }
 
            template <typename Result_, typename UnwrappedVisitor_>
            Result_ accept_returning(const UnwrappedVisitor_ & v, const Result_ & r = Result_()) const
            {
                WrappedNonVoidResultVisitor<typename MakeTypeListConst<VisitableTypeList_>::Type, Result_, const UnwrappedVisitor_> vv(v, r);
                _real_accept_const(vv);
                return vv.result;
            }
 
            template <typename Case_, typename... Cases_>
            auto make_accept_returning(const Case_ & firstcase, const Cases_ & ... cases) const -> CallResultType<Case_>
            {
                return this->accept_returning<CallResultType<Case_> >(make_visitor(firstcase, cases...));
            }
 
            template <typename... Cases_>
            void make_accept(const Cases_ & ... cases) const
            {
                this->accept(make_visitor(cases...));
            }
    };
 
    template <typename BaseClass_, typename RealClass_>
    class PALUDIS_VISIBLE ImplementAcceptMethods :
        public virtual DeclareAbstractAcceptMethods<BaseClass_, typename BaseClass_::VisitableTypeList>
    {
        private:
            void _real_accept(WrappedVisitorBase<typename BaseClass_::VisitableTypeList> & v) override
            {
                v.forward_visit(*static_cast<RealClass_ *>(this));
            };
 
            void _real_accept_const(WrappedVisitorBase<typename MakeTypeListConst<typename BaseClass_::VisitableTypeList>::Type> & v) const override
            {
                v.forward_visit(*static_cast<const RealClass_ *>(this));
            };
    };
}
 
#endif