GteRangeIteration.h

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// David Eberly, Geometric Tools, Redmond WA 98052
// Copyright (c) 1998-2017
// Distributed under the Boost Software License, Version 1.0.
// http://www.boost.org/LICENSE_1_0.txt
// http://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
// File Version: 3.0.0 (2016/06/19)

#pragma once

#include <GTEngineDEF.h>
#include <iterator>
#include <type_traits>

// For information on range-based for-loops, see
// http://en.cppreference.com/w/cpp/language/range-for

namespace gte
{

// The function gte::reverse supports reverse iteration in range-based
// for-loops using the auto keyword.  For example,
//
//   std::vector<int> numbers(4);
//   int i = 0;
//   for (auto& number : numbers)
//   {
//       number = i++;
//       std::cout << number << ' ';
//   }
//   // Output:  0 1 2 3
//
//   for (auto& number : gte::reverse(numbers))
//   {
//       std::cout << number << ' ';
//   }
//   // Output:  3 2 1 0

template <typename Iterator>
class ReversalObject
{
public:
    ReversalObject(Iterator begin, Iterator end)
        :
        mBegin(begin),
        mEnd(end)
    {
    }

    Iterator begin() const { return mBegin; }
    Iterator end() const { return mEnd; }

private:
    Iterator mBegin, mEnd;
};

template
<
    typename Iterable,
    typename Iterator = decltype(std::begin(std::declval<Iterable>())),
    typename ReverseIterator = std::reverse_iterator<Iterator>
>
ReversalObject<ReverseIterator> reverse(Iterable&& range)
{
    return ReversalObject<ReverseIterator>(
        ReverseIterator(std::end(range)),
        ReverseIterator(std::begin(range)));
}

}