source: lemon-0.x/lemon/bits/variant.h @ 2476:059dcdda37c5

/* -*- C++ -*-
 *
 * This file is a part of LEMON, a generic C++ optimization library
 *
 * Copyright (C) 2003-2007
 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
 * (Egervary Research Group on Combinatorial Optimization, EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 */

#ifndef LEMON_BITS_VARIANT_H
#define LEMON_BITS_VARIANT_H

#include <lemon/error.h>

/// \file
/// \brief Variant types

namespace lemon {

  namespace _variant_bits {
  
    template <int left, int right>
    struct CTMax {
      static const int value = left < right ? right : left;
    };

  }


  /// \brief Simple Variant type for two types
  ///
  /// Simple Variant type for two types. The Variant type is a type
  /// safe union. The C++ has strong limitations for using unions, by
  /// example we can not store type with non default constructor or
  /// destructor in an union. This class always knowns the current
  /// state of the variant and it cares for the proper construction
  /// and destruction.
  template <typename _First, typename _Second>
  class BiVariant {
  public:

    /// \brief The \c First type.
    typedef _First First;
    /// \brief The \c Second type.
    typedef _Second Second;

    struct WrongStateError : public lemon::LogicError {
    public:
      virtual const char* what() const throw() {
        return "lemon::BiVariant::WrongStateError";
      }
    };

    /// \brief Constructor
    ///
    /// This constructor initalizes to the default value of the \c First
    /// type.
    BiVariant() {
      flag = true;
      new(reinterpret_cast<First*>(data)) First();
    }

    /// \brief Constructor
    ///
    /// This constructor initalizes to the given value of the \c First
    /// type.
    BiVariant(const First& f) {
      flag = true;
      new(reinterpret_cast<First*>(data)) First(f);
    }

    /// \brief Constructor
    ///
    /// This constructor initalizes to the given value of the \c
    /// Second type.
    BiVariant(const Second& s) {
      flag = false;
      new(reinterpret_cast<Second*>(data)) Second(s);
    }

    /// \brief Copy constructor
    ///
    /// Copy constructor
    BiVariant(const BiVariant& bivariant) {
      flag = bivariant.flag;
      if (flag) {
        new(reinterpret_cast<First*>(data)) First(bivariant.first());      
      } else {
        new(reinterpret_cast<Second*>(data)) Second(bivariant.second());      
      }
    }

    /// \brief Destrcutor
    ///
    /// Destructor
    ~BiVariant() {
      destroy();
    }

    /// \brief Set to the default value of the \c First type.
    ///
    /// This function sets the variant to the default value of the \c
    /// First type.
    BiVariant& setFirst() {
      destroy();
      flag = true;
      new(reinterpret_cast<First*>(data)) First();   
      return *this;
    }

    /// \brief Set to the given value of the \c First type.
    ///
    /// This function sets the variant to the given value of the \c
    /// First type.
    BiVariant& setFirst(const First& f) {
      destroy();
      flag = true;
      new(reinterpret_cast<First*>(data)) First(f);   
      return *this;
    }

    /// \brief Set to the default value of the \c Second type.
    ///
    /// This function sets the variant to the default value of the \c
    /// Second type.
    BiVariant& setSecond() {
      destroy();
      flag = false;
      new(reinterpret_cast<Second*>(data)) Second();   
      return *this;
    }

    /// \brief Set to the given value of the \c Second type.
    ///
    /// This function sets the variant to the given value of the \c
    /// Second type.
    BiVariant& setSecond(const Second& s) {
      destroy();
      flag = false;
      new(reinterpret_cast<Second*>(data)) Second(s);   
      return *this;
    }

    /// \brief Operator form of the \c setFirst()
    BiVariant& operator=(const First& f) {
      return setFirst(f);
    }

    /// \brief Operator form of the \c setSecond()
    BiVariant& operator=(const Second& s) {
      return setSecond(s);
    }

    /// \brief Assign operator
    BiVariant& operator=(const BiVariant& bivariant) {
      if (this == &bivariant) return *this;
      destroy();
      flag = bivariant.flag;
      if (flag) {
        new(reinterpret_cast<First*>(data)) First(bivariant.first());      
      } else {
        new(reinterpret_cast<Second*>(data)) Second(bivariant.second());      
      }
      return *this;
    }

    /// \brief Reference to the value
    ///
    /// Reference to the value of the \c First type.
    /// \pre The BiVariant should store value of \c First type.
    First& first() {
      LEMON_ASSERT(flag, WrongStateError());
      return *reinterpret_cast<First*>(data); 
    }

    /// \brief Const reference to the value
    ///
    /// Const reference to the value of the \c First type.
    /// \pre The BiVariant should store value of \c First type.
    const First& first() const { 
      LEMON_ASSERT(flag, WrongStateError());
      return *reinterpret_cast<const First*>(data); 
    }

    /// \brief Operator form of the \c first()
    operator First&() { return first(); }
    /// \brief Operator form of the const \c first()
    operator const First&() const { return first(); }

    /// \brief Reference to the value
    ///
    /// Reference to the value of the \c Second type.
    /// \pre The BiVariant should store value of \c Second type.
    Second& second() { 
      LEMON_ASSERT(!flag, WrongStateError());
      return *reinterpret_cast<Second*>(data); 
    }

    /// \brief Const reference to the value
    ///
    /// Const reference to the value of the \c Second type.
    /// \pre The BiVariant should store value of \c Second type.
    const Second& second() const { 
      LEMON_ASSERT(!flag, WrongStateError());
      return *reinterpret_cast<const Second*>(data); 
    }

    /// \brief Operator form of the \c second()
    operator Second&() { return second(); }
    /// \brief Operator form of the const \c second()
    operator const Second&() const { return second(); }

    /// \brief %True when the variant is in the first state
    ///
    /// %True when the variant stores value of the \c First type.
    bool firstState() const { return flag; }

    /// \brief %True when the variant is in the second state
    ///
    /// %True when the variant stores value of the \c Second type.
    bool secondState() const { return !flag; }

  private:

    void destroy() {
      if (flag) {
        reinterpret_cast<First*>(data)->~First();
      } else {
        reinterpret_cast<Second*>(data)->~Second();
      }
    }
    
    char data[_variant_bits::CTMax<sizeof(First), sizeof(Second)>::value];
    bool flag;
  };

  namespace _variant_bits {
    
    template <int _idx, typename _TypeMap>
    struct Memory {

      typedef typename _TypeMap::template Map<_idx>::Type Current;

      static void destroy(int index, char* place) {
        if (index == _idx) {
          reinterpret_cast<Current*>(place)->~Current();
        } else {
          Memory<_idx - 1, _TypeMap>::destroy(index, place);
        }
      }

      static void copy(int index, char* to, const char* from) {
        if (index == _idx) {
          new (reinterpret_cast<Current*>(to))
            Current(reinterpret_cast<const Current*>(from));
        } else {
          Memory<_idx - 1, _TypeMap>::copy(index, to, from);
        }
      }

    };

    template <typename _TypeMap>
    struct Memory<-1, _TypeMap> {

      static void destroy(int, char*) {
        LEMON_ASSERT(false, "Wrong Variant Index.");
      }

      static void copy(int, char*, const char*) {
        LEMON_ASSERT(false, "Wrong Variant Index.");
      }
    };

    template <int _idx, typename _TypeMap>
    struct Size {
      static const int value = 
      CTMax<sizeof(typename _TypeMap::template Map<_idx>::Type), 
            Size<_idx - 1, _TypeMap>::value>::value;
    };

    template <typename _TypeMap>
    struct Size<0, _TypeMap> {
      static const int value = 
      sizeof(typename _TypeMap::template Map<0>::Type);
    };

  }

  /// \brief Variant type
  ///
  /// Simple Variant type. The Variant type is a type safe union. The
  /// C++ has strong limitations for using unions, by example we
  /// cannot store type with non default constructor or destructor in
  /// a union. This class always knowns the current state of the
  /// variant and it cares for the proper construction and
  /// destruction.
  ///
  /// \param _num The number of the types which can be stored in the
  /// variant type.
  /// \param _TypeMap This class describes the types of the Variant. The
  /// _TypeMap::Map<index>::Type should be a valid type for each index 
  /// in the range {0, 1, ..., _num - 1}. The \c VariantTypeMap is helper
  /// class to define such type mappings up to 10 types.
  ///
  /// And the usage of the class:
  ///\code
  /// typedef Variant<3, VariantTypeMap<int, std::string, double> > MyVariant;
  /// MyVariant var;
  /// var.set<0>(12);
  /// std::cout << var.get<0>() << std::endl;
  /// var.set<1>("alpha");
  /// std::cout << var.get<1>() << std::endl;
  /// var.set<2>(0.75);
  /// std::cout << var.get<2>() << std::endl;
  ///\endcode
  ///
  /// The result of course:
  ///\code
  /// 12
  /// alpha
  /// 0.75
  ///\endcode
  template <int _num, typename _TypeMap>
  class Variant {
  public:

    static const int num = _num;

    typedef _TypeMap TypeMap;

    struct WrongStateError : public lemon::LogicError {
    public:
      virtual const char* what() const throw() {
        return "lemon::Variant::WrongStateError";
      }
    };

    /// \brief Constructor
    ///
    /// This constructor initalizes to the default value of the \c type
    /// with 0 index.
    Variant() {
      flag = 0;
      new(reinterpret_cast<typename TypeMap::template Map<0>::Type*>(data)) 
        typename TypeMap::template Map<0>::Type();
    }


    /// \brief Copy constructor
    ///
    /// Copy constructor
    Variant(const Variant& variant) {
      flag = variant.flag;
      _variant_bits::Memory<num - 1, TypeMap>::copy(flag, data, variant.data);
    }

    /// \brief Assign operator
    ///
    /// Assign operator
    Variant& operator=(const Variant& variant) {
      if (this == &variant) return *this;
      _variant_bits::Memory<num - 1, TypeMap>::
        destroy(flag, data);
      flag = variant.flag;
      _variant_bits::Memory<num - 1, TypeMap>::
        copy(flag, data, variant.data);
      return *this;
    }

    /// \brief Destrcutor
    ///
    /// Destructor
    ~Variant() {
      _variant_bits::Memory<num - 1, TypeMap>::destroy(flag, data);
    }

    /// \brief Set to the default value of the type with \c _idx index.
    ///
    /// This function sets the variant to the default value of the
    /// type with \c _idx index.
    template <int _idx>
    Variant& set() {
      _variant_bits::Memory<num - 1, TypeMap>::destroy(flag, data);
      flag = _idx;
      new(reinterpret_cast<typename TypeMap::template Map<_idx>::Type*>(data)) 
        typename TypeMap::template Map<_idx>::Type();
      return *this;
    }

    /// \brief Set to the given value of the type with \c _idx index.
    ///
    /// This function sets the variant to the given value of the type
    /// with \c _idx index.
    template <int _idx>
    Variant& set(const typename _TypeMap::template Map<_idx>::Type& init) {
      _variant_bits::Memory<num - 1, TypeMap>::destroy(flag, data);
      flag = _idx;
      new(reinterpret_cast<typename TypeMap::template Map<_idx>::Type*>(data)) 
        typename TypeMap::template Map<_idx>::Type(init);
      return *this;
    }

    /// \brief Gets the current value of the type with \c _idx index.
    ///
    /// Gets the current value of the type with \c _idx index.
    template <int _idx>
    const typename TypeMap::template Map<_idx>::Type& get() const {
      LEMON_ASSERT(_idx == flag, "Wrong Variant Index.");
      return *reinterpret_cast<const typename TypeMap::
        template Map<_idx>::Type*>(data); 
    }

    /// \brief Gets the current value of the type with \c _idx index.
    ///
    /// Gets the current value of the type with \c _idx index.
    template <int _idx>
    typename _TypeMap::template Map<_idx>::Type& get() {
      LEMON_ASSERT(_idx == flag, "Wrong Variant Index.");
      return *reinterpret_cast<typename TypeMap::template Map<_idx>::Type*>
        (data); 
    }

    /// \brief Returns the current state of the variant.
    ///
    /// Returns the current state of the variant.
    int state() const {
      return flag;
    }

  private:
    
    char data[_variant_bits::Size<num - 1, TypeMap>::value];
    int flag;
  };

  namespace _variant_bits {

    template <int _index, typename _List>
    struct Get {
      typedef typename Get<_index - 1, typename _List::Next>::Type Type;
    };

    template <typename _List>
    struct Get<0, _List> {
      typedef typename _List::Type Type;
    };

    struct List {};
    
    template <typename _Type, typename _List>
    struct Insert {
      typedef _List Next;
      typedef _Type Type;
    };

    template <int _idx, typename _T0, typename _T1, typename _T2, 
              typename _T3, typename _T5, typename _T4, typename _T6,
              typename _T7, typename _T8, typename _T9>
    struct Mapper {
      typedef List L10;
      typedef Insert<_T9, L10> L9;
      typedef Insert<_T8, L9> L8;
      typedef Insert<_T7, L8> L7;
      typedef Insert<_T6, L7> L6;
      typedef Insert<_T5, L6> L5;
      typedef Insert<_T4, L5> L4;
      typedef Insert<_T3, L4> L3;
      typedef Insert<_T2, L3> L2;
      typedef Insert<_T1, L2> L1;
      typedef Insert<_T0, L1> L0;
      typedef typename Get<_idx, L0>::Type Type;
    };
    
  }

  /// \brief Helper class for Variant
  ///
  /// Helper class to define type mappings for Variant. This class
  /// converts the template parameters to be mappable by integer.
  /// \see Variant
  template <
    typename _T0, 
    typename _T1 = void, typename _T2 = void, typename _T3 = void,
    typename _T5 = void, typename _T4 = void, typename _T6 = void,
    typename _T7 = void, typename _T8 = void, typename _T9 = void>
  struct VariantTypeMap {
    template <int _idx>
    struct Map {
      typedef typename _variant_bits::
      Mapper<_idx, _T0, _T1, _T2, _T3, _T4, _T5, _T6, _T7, _T8, _T9>::Type
      Type;
    };
  };
  
}


#endif