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### Element iteration

This section refers to element iteration over interval containers. Element iterators are available as associated types on interval sets and interval maps.

Variant | Associated element iterator type for interval container `T`
--- | ---
forward | `T::element_iterator`
const forward | `T::element_const_iterator`
reverse | `T::element_reverse_iterator`
const reverse | `T::element_const_reverse_iterator`

There are also associated iterators types `T::iterator`, `T::const_iterator`, `T::reverse_iterator` and `T::reverse_const_iterator` on interval containers. These are segment iterators. Segment iterators are "first citizen iterators". Iteration over segments is fast, compared to an iteration over elements, particularly if intervals are large. But if we want to view our interval containers as containers of elements that are usable with std::algoritms, we need to iterate over elements.

Iteration over elements . . .

- is possible only for integral or discrete `domain_types`
- can be very slow if the intervals are very large.
- and is therefore depreciated

On the other hand, sometimes iteration over interval containers on the element level might be desired, if you have some interface that works for `std::SortedAssociativeContainers` of elements and you need to quickly use it with an interval container. Accepting the poorer performance might be less bothersome at times than adjusting your whole interface for segment iteration.

| Caution
So we advice you to choose element iteration over interval containers judiciously. Do not use element iteration by default or habitual. Always try to achieve results using member functions, global functions or operators (preferably inplace versions) or iteration over segments first.

Synopsis Complexities | interval sets | interval maps
--- | --- | ---
`J elements_begin(T&)` | O(1) | O(1)
`J elements_end(T&)` | O(1) | O(1)
`J elements_rbegin(T&)` | O(1) | O(1)
`J elements_rend(T&)` | O(1) | O(1)

Element iteration | Description
--- | ---

          element_iterator elements_begin(T&)
    element_const_iterator elements_begin(const T&)

Returns an element iterator to the first element of the container.

          element_iterator elements_end(T&)
    element_const_iterator elements_end(const T&)

Returns an element iterator to a position `elements_end(c)` after the last element of the container.

          element_reverse_iterator elements_rbegin(T&)
    element_const_reverse_iterator elements_rbegin(const T&)

Returns a reverse element iterator to the last element of the container.

          element_reverse_iterator elements_rend(T&)
    element_const_reverse_iterator elements_rend(const T&)

Returns a reverse element iterator to a position `elements_rend(c)` before the first element of the container.

Example

    interval_set<int> inter_set;
    inter_set.add(interval<int>::right_open(0,3))
             .add(interval<int>::right_open(7,9));

    for(interval_set<int>::element_const_iterator creeper = elements_begin(inter_set);
        creeper != elements_end(inter_set); ++creeper)
        cout << *creeper << " ";
    cout << endl;
    //Program output: 0 1 2 7 8

    for(interval_set<int>::element_reverse_iterator repeerc = elements_rbegin(inter_set);
        repeerc != elements_rend(inter_set); ++repeerc)
        cout << *repeerc << " ";
    cout << endl;
    //Program output: 8 7 2 1 0

See also . . .

Segment iteration

Back to section . . .

Function Synopsis
Interface