簡介

該適配器接受兩個參數：

• 指向進行重新排列的區間 V 的一個迭代器
• 定義如何重新排列 V 中的元素的方案

注意，排列迭代器並不限於對給定區間 V 進行嚴格的排列。重排列迭代器的開始至結尾的距離可以小於區間 V 的大小，這樣排列迭代器只是提供了對 V 的一個子區間的排列。索引也不需要是唯一的。在這種情況下，必須要注意排列迭代器的末尾要依據該索引的迭代器的末尾來完整地定義。

參考

template< class ElementIterator
        , class IndexIterator
        , class ValueT        = use_default
        , class CategoryT     = use_default
        , class ReferenceT    = use_default
        , class DifferenceT   = use_default >
class permutation_iterator
{
public:
  permutation_iterator();
  explicit permutation_iterator(ElementIterator x, IndexIterator y);

  template< class OEIter, class OIIter, class V, class C, class R, class D >
  permutation_iterator(
      permutation_iterator<OEIter, OIIter, V, C, R, D> const& r
      , typename enable_if_convertible<OEIter, ElementIterator>::type* = 0
      , typename enable_if_convertible<OIIter, IndexIterator>::type* = 0
      );
  reference operator*() const;
  permutation_iterator& operator++();
  ElementIterator const& base() const;
private:
  ElementIterator m_elt;      // exposition only
  IndexIterator m_order;      // exposition only
};

template <class ElementIterator, class IndexIterator>
permutation_iterator<ElementIterator, IndexIterator>
make_permutation_iterator( ElementIterator e, IndexIterator i);

template< class OEIter, class OIIter, class V, class C, class R, class D >
permutation_iterator(
    permutation_iterator<OEIter, OIIter, V, C, R, D> const& r
    , typename enable_if_convertible<OEIter, ElementIterator>::type* = 0
    , typename enable_if_convertible<OIIter, IndexIterator>::type* = 0
    );

template <class ElementIterator, class IndexIterator>
permutation_iterator<ElementIterator, IndexIterator>
make_permutation_iterator(ElementIterator e, IndexIterator i);

例子

using namespace boost;
int i = 0;

typedef std::vector< int > element_range_type;
typedef std::list< int > index_type;

static const int element_range_size = 10;
static const int index_size = 4;

element_range_type elements( element_range_size );
for(element_range_type::iterator el_it = elements.begin() ; el_it != elements.end() ; ++el_it)
  *el_it = std::distance(elements.begin(), el_it);

index_type indices( index_size );
for(index_type::iterator i_it = indices.begin() ; i_it != indices.end() ; ++i_it )
  *i_it = element_range_size - index_size + std::distance(indices.begin(), i_it);
std::reverse( indices.begin(), indices.end() );

typedef permutation_iterator< element_range_type::iterator, index_type::iterator > permutation_type;
permutation_type begin = make_permutation_iterator( elements.begin(), indices.begin() );
permutation_type it = begin;
permutation_type end = make_permutation_iterator( elements.begin(), indices.end() );

std::cout << "The original range is : ";
std::copy( elements.begin(), elements.end(), std::ostream_iterator< int >( std::cout, " " ) );
std::cout << "\n";

std::cout << "The reindexing scheme is : ";
std::copy( indices.begin(), indices.end(), std::ostream_iterator< int >( std::cout, " " ) );
std::cout << "\n";

std::cout << "The permutated range is : ";
std::copy( begin, end, std::ostream_iterator< int >( std::cout, " " ) );
std::cout << "\n";

std::cout << "Elements at even indices in the permutation : ";
it = begin;
for(i = 0; i < index_size / 2 ; ++i, it+=2 ) std::cout << *it << " ";
std::cout << "\n";

std::cout << "Permutation backwards : ";
it = begin + (index_size);
assert( it != begin );
for( ; it-- != begin ; ) std::cout << *it << " ";
std::cout << "\n";

std::cout << "Iterate backward with stride 2 : ";
it = begin + (index_size - 1);
for(i = 0 ; i < index_size / 2 ; ++i, it-=2 ) std::cout << *it << " ";
std::cout << "\n";

輸出結果是：

The original range is : 0 1 2 3 4 5 6 7 8 9
The reindexing scheme is : 9 8 7 6
The permutated range is : 9 8 7 6
Elements at even indices in the permutation : 9 7
Permutation backwards : 6 7 8 9
Iterate backward with stride 2 : 6 8

該例子的源代碼請見 這裡。