path: root/shared/loki/HierarchyGenerators.h

////////////////////////////////////////////////////////////////////////////////
// The Loki Library
// Copyright (c) 2001 by Andrei Alexandrescu
// This code accompanies the book:
// Alexandrescu, Andrei. "Modern C++ Design: Generic Programming and Design
//     Patterns Applied". Copyright (c) 2001. Addison-Wesley.
// Permission to use, copy, modify, distribute and sell this software for any
//     purpose is hereby granted without fee, provided that the above copyright
//     notice appear in all copies and that both that copyright notice and this
//     permission notice appear in supporting documentation.
// The author or Addison-Wesley Longman make no representations about the
//     suitability of this software for any purpose. It is provided "as is"
//     without express or implied warranty.
////////////////////////////////////////////////////////////////////////////////
#ifndef LOKI_HIERARCHYGENERATORS_INC_
#define LOKI_HIERARCHYGENERATORS_INC_

// $Id: HierarchyGenerators.h 751 2006-10-17 19:50:37Z syntheticpp $


#include "Typelist.h"
#include "TypeTraits.h"
#include "EmptyType.h"

namespace Loki
{
#if defined(_MSC_VER) && _MSC_VER >= 1300
#pragma warning( push )
// 'class1' : base-class 'class2' is already a base-class of 'class3'
#pragma warning( disable : 4584 )
#endif // _MSC_VER

////////////////////////////////////////////////////////////////////////////////
// class template GenScatterHierarchy
// Generates a scattered hierarchy starting from a typelist and a template
// Invocation (TList is a typelist, Unit is a template of one arg):
// GenScatterHierarchy<TList, Unit>
// The generated class inherits all classes generated by instantiating the
// template 'Unit' with the types contained in TList
////////////////////////////////////////////////////////////////////////////////

namespace Private
{
// The following type helps to overcome subtle flaw in the original
// implementation of GenScatterHierarchy.
// The flaw is revealed when the input type list of GenScatterHierarchy
// contains more then one element of the same type (e.g. LOKI_TYPELIST_2(int, int)).
// In this case GenScatterHierarchy will contain multiple bases of the same
// type and some of them will not be reachable (per 10.3).
// For example before the fix the first element of Tuple<LOKI_TYPELIST_2(int, int)>
// is not reachable in any way!
template<class, class>
struct ScatterHierarchyTag;
}

template <class TList, template <class> class Unit>
class GenScatterHierarchy;

template <class T1, class T2, template <class> class Unit>
class GenScatterHierarchy<Typelist<T1, T2>, Unit>
    : public GenScatterHierarchy<Private::ScatterHierarchyTag<T1, T2>, Unit>
    , public GenScatterHierarchy<T2, Unit>
{
public:
    typedef Typelist<T1, T2> TList;
    // Insure that LeftBase is unique and therefore reachable
    typedef GenScatterHierarchy<Private::ScatterHierarchyTag<T1, T2>, Unit> LeftBase;
    typedef GenScatterHierarchy<T2, Unit> RightBase;
    template <typename T> struct Rebind
    {
        typedef Unit<T> Result;
    };
};

// In the middle *unique* class that resolve possible ambiguity
template <class T1, class T2, template <class> class Unit>
class GenScatterHierarchy<Private::ScatterHierarchyTag<T1, T2>, Unit>
    : public GenScatterHierarchy<T1, Unit>
{
};

template <class AtomicType, template <class> class Unit>
class GenScatterHierarchy : public Unit<AtomicType>
{
    typedef Unit<AtomicType> LeftBase;
    template <typename T> struct Rebind
    {
        typedef Unit<T> Result;
    };
};

template <template <class> class Unit>
class GenScatterHierarchy<NullType, Unit>
{
    template <typename T> struct Rebind
    {
        typedef Unit<T> Result;
    };
};

////////////////////////////////////////////////////////////////////////////////
// function template Field
// Accesses a field in an object of a type generated with GenScatterHierarchy
// Invocation (obj is an object of a type H generated with GenScatterHierarchy,
//     T is a type in the typelist used to generate H):
// Field<T>(obj)
// returns a reference to Unit<T>, where Unit is the template used to generate H
////////////////////////////////////////////////////////////////////////////////

template <class T, class H>
typename H::template Rebind<T>::Result& Field(H& obj)
{
    return obj;
}

template <class T, class H>
const typename H::template Rebind<T>::Result& Field(const H& obj)
{
    return obj;
}

////////////////////////////////////////////////////////////////////////////////
// function template TupleUnit
// The building block of tuples
////////////////////////////////////////////////////////////////////////////////

template <class T>
struct TupleUnit
{
    T value_;
    operator T& () { return value_; }
    operator const T& () const { return value_; }
};

////////////////////////////////////////////////////////////////////////////////
// class template Tuple
// Implements a tuple class that holds a number of values and provides field
//     access to them via the Field function (below)
////////////////////////////////////////////////////////////////////////////////

template <class TList>
struct Tuple : public GenScatterHierarchy<TList, TupleUnit>
{
};

////////////////////////////////////////////////////////////////////////////////
// helper class template FieldHelper
// See Field below
////////////////////////////////////////////////////////////////////////////////

template <class H, unsigned int i> struct FieldHelper;

template <class H>
struct FieldHelper<H, 0>
{
    typedef typename H::TList::Head ElementType;
    typedef typename H::template Rebind<ElementType>::Result UnitType;

    enum
    {
        isTuple = Conversion<UnitType, TupleUnit<ElementType> >::sameType,
        isConst = TypeTraits<H>::isConst
    };

    typedef const typename H::LeftBase ConstLeftBase;

    typedef typename Select < isConst, ConstLeftBase,
            typename H::LeftBase >::Result LeftBase;

    typedef typename Select < isTuple, ElementType,
            UnitType >::Result UnqualifiedResultType;

    typedef typename Select < isConst, const UnqualifiedResultType,
            UnqualifiedResultType >::Result ResultType;

    static ResultType& Do(H& obj)
    {
        LeftBase& leftBase = obj;
        return leftBase;
    }
};

template <class H, unsigned int i>
struct FieldHelper
{
    typedef typename TL::TypeAt<typename H::TList, i>::Result ElementType;
    typedef typename H::template Rebind<ElementType>::Result UnitType;

    enum
    {
        isTuple = Conversion<UnitType, TupleUnit<ElementType> >::sameType,
        isConst = TypeTraits<H>::isConst
    };

    typedef const typename H::RightBase ConstRightBase;

    typedef typename Select < isConst, ConstRightBase,
            typename H::RightBase >::Result RightBase;

    typedef typename Select < isTuple, ElementType,
            UnitType >::Result UnqualifiedResultType;

    typedef typename Select < isConst, const UnqualifiedResultType,
            UnqualifiedResultType >::Result ResultType;

    static ResultType& Do(H& obj)
    {
        RightBase& rightBase = obj;
        return FieldHelper < RightBase, i - 1 >::Do(rightBase);
    }
};

////////////////////////////////////////////////////////////////////////////////
// function template Field
// Accesses a field in an object of a type generated with GenScatterHierarchy
// Invocation (obj is an object of a type H generated with GenScatterHierarchy,
//     i is the index of a type in the typelist used to generate H):
// Field<i>(obj)
// returns a reference to Unit<T>, where Unit is the template used to generate H
//     and T is the i-th type in the typelist
////////////////////////////////////////////////////////////////////////////////

template <int i, class H>
typename FieldHelper<H, i>::ResultType&
Field(H& obj)
{
    return FieldHelper<H, i>::Do(obj);
}

//    template <int i, class H>
//    const typename FieldHelper<H, i>::ResultType&
//    Field(const H& obj)
//    {
//        return FieldHelper<H, i>::Do(obj);
//    }

////////////////////////////////////////////////////////////////////////////////
// class template GenLinearHierarchy
// Generates a linear hierarchy starting from a typelist and a template
// Invocation (TList is a typelist, Unit is a template of two args):
// GenScatterHierarchy<TList, Unit>
////////////////////////////////////////////////////////////////////////////////

template
<
class TList,
      template <class AtomicType, class Base> class Unit,
      class Root = EmptyType
      >
class GenLinearHierarchy;

template
<
class T1,
      class T2,
      template <class, class> class Unit,
      class Root
      >
class GenLinearHierarchy<Typelist<T1, T2>, Unit, Root>
    : public Unit< T1, GenLinearHierarchy<T2, Unit, Root> >
{
};

template
<
class T,
      template <class, class> class Unit,
      class Root
      >
class GenLinearHierarchy<Typelist<T, NullType>, Unit, Root>
    : public Unit<T, Root>
{
};

template
<
template <class, class> class Unit,
         class Root
         >
class GenLinearHierarchy<NullType , Unit, Root>
    : public Root // is this better: Unit<NullType, Root> ?
{
};

#if defined(_MSC_VER) && _MSC_VER >= 1300
#pragma warning( pop )
#endif
}   // namespace Loki

#endif // end file guardian