proxy_iterator.h

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/* This file is part of Cloudy and is copyright (C)1978-2022 by Gary J. Ferland and
 * others.  For conditions of distribution and use see copyright notice in license.txt */

#ifndef PROXY_ITERATOR_H_
#define PROXY_ITERATOR_H_
#include <algorithm> // For std::swap

//
// Smart pointer class extends a proxy class on a list to provide
// random_access_iterator functionality
//
// Requirements: base class P has members
//   list_type => typedef for type of base list class
//   m_list => pointer to base list class
//   m_index => offset to current list item
//   ProxyIterator<P,C> is a friend class
//
// Iterator functionality alters the value of m_index
//

template<bool, class T>
struct EnableIf_c
{
        // In general just pass through type
        typedef T type;
};
template<class T>
struct EnableIf_c<false, T>
{
        // unless argument is false, in which case map to private internal
        // type
private:
        class Invalid {};
public:
        typedef Invalid type;
};
template <class Cond, class T>
        struct EnableIf: EnableIf_c<Cond::value, T>
{
};
template <class T, class U>
struct IsSame
{
        static const bool value = false;
};
template <class T>
struct IsSame<T,T>
{
        static const bool value = true;
};
template <class T>
struct Not
{
   static const bool value = ! T::value;
};

template<class P, class C>
class ProxyIterator
{
        P proxy;
        typedef EnableIf<Not<IsSame<P,C> >,
                ProxyIterator<C,C> > const_iterator_type_1;
        typedef typename const_iterator_type_1::type const_iterator_type;
public:
        typedef P value_type;
        typedef int difference_type;
        typedef random_access_iterator_tag iterator_category;
        typedef const value_type &reference;
        typedef const value_type *pointer;
        // Construction
        explicit ProxyIterator(typename P::list_type* list, int index) : 
        proxy(list, index) {}
        ProxyIterator(const ProxyIterator &other) : 
        proxy(other.proxy.m_list, other.proxy.m_index) {}
        explicit ProxyIterator(void) : proxy(NULL, 0) {}
        ProxyIterator &operator=(ProxyIterator other) // Temporary is intentional
        {
                swap(other);
                return *this;
        }
        operator const_iterator_type() const 
        { 
                return const_iterator_type(proxy.m_list, proxy.m_index); 
        }
        // swap member function (to implement canonical exception-safe assignment)
        void swap(ProxyIterator other)
        {
                std::swap(proxy.m_list,other.proxy.m_list);
                std::swap(proxy.m_index,other.proxy.m_index);
        }
        // Associated test (not required)
        bool associated() const
        {
                return proxy.m_list != NULL;
        }
        // Equality
        bool equals(const ProxyIterator &other) const
        {
                return other.proxy.m_list == proxy.m_list && 
                        other.proxy.m_index == proxy.m_index;
        }
        // Dereference
        reference operator*() const
        {
                return proxy;
        }
        pointer operator->() const
        {
                // Return a pointer to the contained proxy, so dereferencing
                // this gives proxy not iterator behaviour.
                return &proxy;
        }
        // Incrementation
        ProxyIterator& operator++()
        {
                ++proxy.m_index;
                return *this;
        }
        ProxyIterator operator++(int)
        {
                ProxyIterator old(*this);
                ++*this;
                return old;
        }
        ProxyIterator& operator--()
        {
                --proxy.m_index;
                return *this;
        }
        ProxyIterator operator--(int)
        {
                ProxyIterator old(*this);
                --*this;
                return old;
        }
        // Member functions to implement standard out-of-line operators
        // Arithmetic
        const ProxyIterator add(difference_type i) const
        {
                return ProxyIterator(proxy.m_list,proxy.m_index+i);
        }
        // Number of steps between (not required)
        difference_type diff(const ProxyIterator &other) const
        {
                return proxy.m_index - other.proxy.m_index;
        }
        // Comparison
        int cmp(const ProxyIterator &other) const
        {
                if (proxy.m_index == other.proxy.m_index)
                        return 0;
                else if (proxy.m_index > other.proxy.m_index)
                        return 1;
                else
                        return -1;
        }
        // Compound assignment
        ProxyIterator& operator+=(difference_type i)
        {
                proxy.m_index += i;
                return *this;
        }
        ProxyIterator &operator-=(difference_type i)
        {
                proxy.m_index -= i;
                return *this;
        }
        // Offset dereference
        const value_type operator[](difference_type i) const
        {
                return P(proxy.m_list,proxy.m_index+i);
        }
};
// Identity
template<class P1, class P2, class C>
        inline bool operator==(const ProxyIterator<P1,C> &a, 
                                                                  const ProxyIterator<P2,C> &b)
{
        return ProxyIterator<C,C>(a).equals(ProxyIterator<C,C>(b));
}
template<class P1,class P2, class C>
inline bool operator!=(const ProxyIterator<P1,C> &a, 
                                                          const ProxyIterator<P2,C> &b)
{
        return !(a == b);
}
// Arithmetic
template<class P, class C>
inline const ProxyIterator<P,C> operator+(
        typename ProxyIterator<P,C>::difference_type i, const ProxyIterator<P,C> &a)
{
        return a.add(i);
}
template<class P, class C>
inline const ProxyIterator<P,C> operator+(
        const ProxyIterator<P,C> &a, typename ProxyIterator<P,C>::difference_type i)
{
        return a.add(i);
}
template<class P, class C>
inline const ProxyIterator<P,C> operator-(
        const ProxyIterator<P,C> &a, typename ProxyIterator<P,C>::difference_type i)
{
        return a.add(-i);
}
// Comparison
template<class P, class C>
inline bool operator>(const ProxyIterator<P,C> &a, 
                                                         const ProxyIterator<P,C> &b)
{
        return a.cmp(b) > 0;
}
template<class P, class C>
inline bool operator>=(const ProxyIterator<P,C> &a, 
                                                          const ProxyIterator<P,C> &b)
{
        return a.cmp(b) >= 0;
}
template<class P, class C>
inline bool operator<(const ProxyIterator<P,C> &a, 
                                                         const ProxyIterator<P,C> &b)
{
        return a.cmp(b) < 0;
}
template<class P, class C>
inline bool operator<=(const ProxyIterator<P,C> &a, 
                                                          const ProxyIterator<P,C> &b)
{
        return a.cmp(b) <= 0;
}
// Iterator difference (not required)
template<class P, class C>
inline typename ProxyIterator<P,C>::difference_type operator-(
        const ProxyIterator<P,C> &a, const ProxyIterator<P,C> &b)
{
        return a.diff(b);
}

#endif