Sequences

## Sequences Sequences — scalable lists |

## Synopsis

    #include <glib.h>

                        GSequence;
    typedef             GSequenceIter;
    gint                (*GSequenceIterCompareFunc)         (GSequenceIter *a,
                                                             GSequenceIter *b,
                                                             gpointer data);

    GSequence *         g_sequence_new                      (GDestroyNotify data_destroy);
    void                g_sequence_free                     (GSequence *seq);
    gint                g_sequence_get_length               (GSequence *seq);
    void                g_sequence_foreach                  (GSequence *seq,
                                                             GFunc func,
                                                             gpointer user_data);
    void                g_sequence_foreach_range            (GSequenceIter *begin,
                                                             GSequenceIter *end,
                                                             GFunc func,
                                                             gpointer user_data);
    void                g_sequence_sort                     (GSequence *seq,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);
    void                g_sequence_sort_iter                (GSequence *seq,
                                                             GSequenceIterCompareFunc cmp_func,
                                                             gpointer cmp_data);

    GSequenceIter *     g_sequence_get_begin_iter           (GSequence *seq);
    GSequenceIter *     g_sequence_get_end_iter             (GSequence *seq);
    GSequenceIter *     g_sequence_get_iter_at_pos          (GSequence *seq,
                                                             gint pos);
    GSequenceIter *     g_sequence_append                   (GSequence *seq,
                                                             gpointer data);
    GSequenceIter *     g_sequence_prepend                  (GSequence *seq,
                                                             gpointer data);
    GSequenceIter *     g_sequence_insert_before            (GSequenceIter *iter,
                                                             gpointer data);
    void                g_sequence_move                     (GSequenceIter *src,
                                                             GSequenceIter *dest);
    void                g_sequence_swap                     (GSequenceIter *a,
                                                             GSequenceIter *b);
    GSequenceIter *     g_sequence_insert_sorted            (GSequence *seq,
                                                             gpointer data,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);
    GSequenceIter *     g_sequence_insert_sorted_iter       (GSequence *seq,
                                                             gpointer data,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);
    void                g_sequence_sort_changed             (GSequenceIter *iter,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);
    void                g_sequence_sort_changed_iter        (GSequenceIter *iter,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);
    void                g_sequence_remove                   (GSequenceIter *iter);
    void                g_sequence_remove_range             (GSequenceIter *begin,
                                                             GSequenceIter *end);
    void                g_sequence_move_range               (GSequenceIter *dest,
                                                             GSequenceIter *begin,
                                                             GSequenceIter *end);
    GSequenceIter *     g_sequence_search                   (GSequence *seq,
                                                             gpointer data,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);
    GSequenceIter *     g_sequence_search_iter              (GSequence *seq,
                                                             gpointer data,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);
    GSequenceIter *     g_sequence_lookup                   (GSequence *seq,
                                                             gpointer data,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);
    GSequenceIter *     g_sequence_lookup_iter              (GSequence *seq,
                                                             gpointer data,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);

    gpointer            g_sequence_get                      (GSequenceIter *iter);
    void                g_sequence_set                      (GSequenceIter *iter,
                                                             gpointer data);

    gboolean            g_sequence_iter_is_begin            (GSequenceIter *iter);
    gboolean            g_sequence_iter_is_end              (GSequenceIter *iter);
    GSequenceIter *     g_sequence_iter_next                (GSequenceIter *iter);
    GSequenceIter *     g_sequence_iter_prev                (GSequenceIter *iter);
    gint                g_sequence_iter_get_position        (GSequenceIter *iter);
    GSequenceIter *     g_sequence_iter_move                (GSequenceIter *iter,
                                                             gint delta);
    GSequence *         g_sequence_iter_get_sequence        (GSequenceIter *iter);

    gint                g_sequence_iter_compare             (GSequenceIter *a,
                                                             GSequenceIter *b);
    GSequenceIter *     g_sequence_range_get_midpoint       (GSequenceIter *begin,
                                                             GSequenceIter *end);

## Description

The GSequence data structure has the API of a list, but is implemented internally with a balanced binary tree. This means that it is possible to maintain a sorted list of n elements in time O(n log n). The data contained in each element can be either integer values, by using of the Type Conversion Macros, or simply pointers to any type of data.

A GSequence is accessed through iterators, represented by a GSequenceIter. An iterator represents a position between two elements of the sequence. For example, the begin iterator represents the gap immediately before the first element of the sequence, and the end iterator represents the gap immediately after the last element. In an empty sequence, the begin and end iterators are the same.

Some methods on GSequence operate on ranges of items. For example `g_sequence_foreach_range()` will call a user-specified function on each element with the given range. The range is delimited by the gaps represented by the passed-in iterators, so if you pass in the begin and end iterators, the range in question is the entire sequence.

The function `g_sequence_get()` is used with an iterator to access the element immediately following the gap that the iterator represents. The iterator is said to point to that element.

Iterators are stable across most operations on a GSequence. For example an iterator pointing to some element of a sequence will continue to point to that element even after the sequence is sorted. Even moving an element to another sequence using for example `g_sequence_move_range()` will not invalidate the iterators pointing to it. The only operation that will invalidate an iterator is when the element it points to is removed from any sequence.

## Details

### GSequence

    typedef struct _GSequence GSequence;

The GSequence struct is an opaque data type representing a Sequence data type.

### GSequenceIter

    typedef struct _GSequenceNode  GSequenceIter;

The GSequenceIter struct is an opaque data type representing an iterator pointing into a GSequence.

### GSequenceIterCompareFunc ()

    gint                (*GSequenceIterCompareFunc)         (GSequenceIter *a,
                                                             GSequenceIter *b,
                                                             gpointer data);

A GSequenceIterCompareFunc is a function used to compare iterators. It must return zero if the iterators compare equal, a negative value if `a` comes before `b`, and a positive value if `b` comes before `a`.

`a` : | a GSequenceIter
`b` : | a GSequenceIter
`data` : | user data
Returns : | zero if the iterators are equal, a negative value if `a` comes before `b`, and a positive value if `b` comes before `a`.

### g_sequence_new ()

    GSequence *         g_sequence_new                      (GDestroyNotify data_destroy);

Creates a new GSequence. The `data_destroy` function, if non-`NULL` will be called on all items when the sequence is destroyed and on items that are removed from the sequence.

`data_destroy` : | a GDestroyNotify function, or `NULL`. [allow-none]
Returns : | a new GSequence

Since 2.14

### g_sequence_free ()

    void                g_sequence_free                     (GSequence *seq);

Frees the memory allocated for `seq`. If `seq` has a data destroy function associated with it, that function is called on all items in `seq`.

`seq` : | a GSequence

Since 2.14

### g_sequence_get_length ()

    gint                g_sequence_get_length               (GSequence *seq);

Returns the length of `seq`

`seq` : | a GSequence
Returns : | the length of `seq`

Since 2.14

### g_sequence_foreach ()

    void                g_sequence_foreach                  (GSequence *seq,
                                                             GFunc func,
                                                             gpointer user_data);

Calls `func` for each item in the sequence passing `user_data` to the function.

`seq` : | a GSequence
`func` : | the function to call for each item in `seq`
`user_data` : | user data passed to `func`

Since 2.14

### g_sequence_foreach_range ()

    void                g_sequence_foreach_range            (GSequenceIter *begin,
                                                             GSequenceIter *end,
                                                             GFunc func,
                                                             gpointer user_data);

Calls `func` for each item in the range (`begin`, `end`) passing `user_data` to the function.

`begin` : | a GSequenceIter
`end` : | a GSequenceIter
`func` : | a GFunc
`user_data` : | user data passed to `func`

Since 2.14

### g_sequence_sort ()

    void                g_sequence_sort                     (GSequence *seq,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);

Sorts `seq` using `cmp_func`.

`cmp_func` is passed two items of `seq` and should return 0 if they are equal, a negative value if the first comes before the second, and a positive value if the second comes before the first.

`seq` : | a GSequence
`cmp_func` : | the function used to sort the sequence
`cmp_data` : | user data passed to `cmp_func`

Since 2.14

### g_sequence_sort_iter ()

    void                g_sequence_sort_iter                (GSequence *seq,
                                                             GSequenceIterCompareFunc cmp_func,
                                                             gpointer cmp_data);

Like `g_sequence_sort()`, but uses a GSequenceIterCompareFunc instead of a GCompareDataFunc as the compare function

`cmp_func` is called with two iterators pointing into `seq`. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.

`seq` : | a GSequence
`cmp_func` : | the function used to compare iterators in the sequence
`cmp_data` : | user data passed to `cmp_func`

Since 2.14

### g_sequence_get_begin_iter ()

    GSequenceIter *     g_sequence_get_begin_iter           (GSequence *seq);

Returns the begin iterator for `seq`.

`seq` : | a GSequence
Returns : | the begin iterator for `seq`.

Since 2.14

### g_sequence_get_end_iter ()

    GSequenceIter *     g_sequence_get_end_iter             (GSequence *seq);

Returns the end iterator for `seg`

`seq` : | a GSequence
Returns : | the end iterator for `seq`

Since 2.14

### g_sequence_get_iter_at_pos ()

    GSequenceIter *     g_sequence_get_iter_at_pos          (GSequence *seq,
                                                             gint pos);

Returns the iterator at position `pos`. If `pos` is negative or larger than the number of items in `seq`, the end iterator is returned.

`seq` : | a GSequence
`pos` : | a position in `seq`, or -1 for the end.
Returns : | The GSequenceIter at position `pos`

Since 2.14

### g_sequence_append ()

    GSequenceIter *     g_sequence_append                   (GSequence *seq,
                                                             gpointer data);

Adds a new item to the end of `seq`.

`seq` : | a GSequence
`data` : | the data for the new item
Returns : | an iterator pointing to the new item

Since 2.14

### g_sequence_prepend ()

    GSequenceIter *     g_sequence_prepend                  (GSequence *seq,
                                                             gpointer data);

Adds a new item to the front of `seq`

`seq` : | a GSequence
`data` : | the data for the new item
Returns : | an iterator pointing to the new item

Since 2.14

### g_sequence_insert_before ()

    GSequenceIter *     g_sequence_insert_before            (GSequenceIter *iter,
                                                             gpointer data);

Inserts a new item just before the item pointed to by `iter`.

`iter` : | a GSequenceIter
`data` : | the data for the new item
Returns : | an iterator pointing to the new item

Since 2.14

### g_sequence_move ()

    void                g_sequence_move                     (GSequenceIter *src,
                                                             GSequenceIter *dest);

Moves the item pointed to by `src` to the position indicated by `dest`. After calling this function `dest` will point to the position immediately after `src`. It is allowed for `src` and `dest` to point into different sequences.

`src` : | a GSequenceIter pointing to the item to move
`dest` : | a GSequenceIter pointing to the position to which the item is moved.

Since 2.14

### g_sequence_swap ()

    void                g_sequence_swap                     (GSequenceIter *a,
                                                             GSequenceIter *b);

Swaps the items pointed to by `a` and `b`. It is allowed for `a` and `b` to point into difference sequences.

`a` : | a GSequenceIter
`b` : | a GSequenceIter

Since 2.14

### g_sequence_insert_sorted ()

    GSequenceIter *     g_sequence_insert_sorted            (GSequence *seq,
                                                             gpointer data,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);

Inserts `data` into `sequence` using `func` to determine the new position. The sequence must already be sorted according to `cmp_func`; otherwise the new position of `data` is undefined.

`cmp_func` is called with two items of the `seq` and `user_data`. It should return 0 if the items are equal, a negative value if the first item comes before the second, and a positive value if the second item comes before the first.

`seq` : | a GSequence
`data` : | the data to insert
`cmp_func` : | the function used to compare items in the sequence
`cmp_data` : | user data passed to `cmp_func`.
Returns : | a GSequenceIter pointing to the new item.

Since 2.14

### g_sequence_insert_sorted_iter ()

    GSequenceIter *     g_sequence_insert_sorted_iter       (GSequence *seq,
                                                             gpointer data,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);

Like `g_sequence_insert_sorted()`, but uses a GSequenceIterCompareFunc instead of a GCompareDataFunc as the compare function.

`iter_cmp` is called with two iterators pointing into `seq`. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.

It is called with two iterators pointing into `seq`. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.

`seq` : | a GSequence
`data` : | data for the new item
`iter_cmp` : | the function used to compare iterators in the sequence
`cmp_data` : | user data passed to `cmp_func`
Returns : | a GSequenceIter pointing to the new item

Since 2.14

### g_sequence_sort_changed ()

    void                g_sequence_sort_changed             (GSequenceIter *iter,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);

Moves the data pointed to a new position as indicated by `cmp_func`. This function should be called for items in a sequence already sorted according to `cmp_func` whenever some aspect of an item changes so that `cmp_func` may return different values for that item.

`cmp_func` is called with two items of the `seq` and `user_data`. It should return 0 if the items are equal, a negative value if the first item comes before the second, and a positive value if the second item comes before the first.

`iter` : | A GSequenceIter
`cmp_func` : | the function used to compare items in the sequence
`cmp_data` : | user data passed to `cmp_func`.

Since 2.14

### g_sequence_sort_changed_iter ()

    void                g_sequence_sort_changed_iter        (GSequenceIter *iter,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);

Like `g_sequence_sort_changed()`, but uses a GSequenceIterCompareFunc instead of a GCompareDataFunc as the compare function.

`iter_cmp` is called with two iterators pointing into `seq`. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.

`iter` : | a GSequenceIter
`iter_cmp` : | the function used to compare iterators in the sequence
`cmp_data` : | user data passed to `cmp_func`

Since 2.14

### g_sequence_remove ()

    void                g_sequence_remove                   (GSequenceIter *iter);

Removes the item pointed to by `iter`. It is an error to pass the end iterator to this function.

If the sequence has a data destroy function associated with it, this function is called on the data for the removed item.

`iter` : | a GSequenceIter

Since 2.14

### g_sequence_remove_range ()

    void                g_sequence_remove_range             (GSequenceIter *begin,
                                                             GSequenceIter *end);

Removes all items in the (`begin`, `end`) range.

If the sequence has a data destroy function associated with it, this function is called on the data for the removed items.

`begin` : | a GSequenceIter
`end` : | a GSequenceIter

Since 2.14

### g_sequence_move_range ()

    void                g_sequence_move_range               (GSequenceIter *dest,
                                                             GSequenceIter *begin,
                                                             GSequenceIter *end);

Inserts the (`begin`, `end`) range at the destination pointed to by ptr. The `begin` and `end` iters must point into the same sequence. It is allowed for `dest` to point to a different sequence than the one pointed into by `begin` and `end`.

If `dest` is NULL, the range indicated by `begin` and `end` is removed from the sequence. If `dest` iter points to a place within the (`begin`, `end`) range, the range does not move.

`dest` : | a GSequenceIter
`begin` : | a GSequenceIter
`end` : | a GSequenceIter

Since 2.14

### g_sequence_search ()

    GSequenceIter *     g_sequence_search                   (GSequence *seq,
                                                             gpointer data,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);

Returns an iterator pointing to the position where `data` would be inserted according to `cmp_func` and `cmp_data`.

`cmp_func` is called with two items of the `seq` and `user_data`. It should return 0 if the items are equal, a negative value if the first item comes before the second, and a positive value if the second item comes before the first.

If you are simply searching for an existing element of the sequence, consider using `g_sequence_lookup()`.

### Note

This function will fail if the data contained in the sequence is unsorted. Use `g_sequence_insert_sorted()` or `g_sequence_insert_sorted_iter()` to add data to your sequence or, if you want to add a large amount of data, call `g_sequence_sort()` after doing unsorted insertions.

`seq` : | a GSequence
`data` : | data for the new item
`cmp_func` : | the function used to compare items in the sequence
`cmp_data` : | user data passed to `cmp_func`.
Returns : | an GSequenceIter pointing to the position where `data` would have been inserted according to `cmp_func` and `cmp_data`.

Since 2.14

### g_sequence_search_iter ()

    GSequenceIter *     g_sequence_search_iter              (GSequence *seq,
                                                             gpointer data,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);

Like `g_sequence_search()`, but uses a GSequenceIterCompareFunc instead of a GCompareDataFunc as the compare function.

`iter_cmp` is called with two iterators pointing into `seq`. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.

If you are simply searching for an existing element of the sequence, consider using `g_sequence_lookup_iter()`.

### Note

This function will fail if the data contained in the sequence is unsorted. Use `g_sequence_insert_sorted()` or `g_sequence_insert_sorted_iter()` to add data to your sequence or, if you want to add a large amount of data, call `g_sequence_sort()` after doing unsorted insertions.

`seq` : | a GSequence
`data` : | data for the new item
`iter_cmp` : | the function used to compare iterators in the sequence
`cmp_data` : | user data passed to `iter_cmp`
Returns : | a GSequenceIter pointing to the position in `seq` where `data` would have been inserted according to `iter_cmp` and `cmp_data`.

Since 2.14

### g_sequence_lookup ()

    GSequenceIter *     g_sequence_lookup                   (GSequence *seq,
                                                             gpointer data,
                                                             GCompareDataFunc cmp_func,
                                                             gpointer cmp_data);

Returns an iterator pointing to the position of the first item found equal to `data` according to `cmp_func` and `cmp_data`. If more than one item is equal, it is not guaranteed that it is the first which is returned. In that case, you can use `g_sequence_iter_next()` and `g_sequence_iter_prev()` to get others.

`cmp_func` is called with two items of the `seq` and `user_data`. It should return 0 if the items are equal, a negative value if the first item comes before the second, and a positive value if the second item comes before the first.

### Note

This function will fail if the data contained in the sequence is unsorted. Use `g_sequence_insert_sorted()` or `g_sequence_insert_sorted_iter()` to add data to your sequence or, if you want to add a large amount of data, call `g_sequence_sort()` after doing unsorted insertions.

`seq` : | a GSequence
`data` : | data to lookup
`cmp_func` : | the function used to compare items in the sequence
`cmp_data` : | user data passed to `cmp_func`.
Returns : | an GSequenceIter pointing to the position of the first item found equal to `data` according to `cmp_func` and `cmp_data`, or `NULL` if no such item exists.

Since 2.28

### g_sequence_lookup_iter ()

    GSequenceIter *     g_sequence_lookup_iter              (GSequence *seq,
                                                             gpointer data,
                                                             GSequenceIterCompareFunc iter_cmp,
                                                             gpointer cmp_data);

Like `g_sequence_lookup()`, but uses a GSequenceIterCompareFunc instead of a GCompareDataFunc as the compare function.

`iter_cmp` is called with two iterators pointing into `seq`. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.

### Note

This function will fail if the data contained in the sequence is unsorted. Use `g_sequence_insert_sorted()` or `g_sequence_insert_sorted_iter()` to add data to your sequence or, if you want to add a large amount of data, call `g_sequence_sort()` after doing unsorted insertions.

`seq` : | a GSequence
`data` : | data to lookup
`iter_cmp` : | the function used to compare iterators in the sequence
`cmp_data` : | user data passed to `iter_cmp`
Returns : | an GSequenceIter pointing to the position of the first item found equal to `data` according to `cmp_func` and `cmp_data`, or `NULL` if no such item exists.

Since 2.28

### g_sequence_get ()

    gpointer            g_sequence_get                      (GSequenceIter *iter);

Returns the data that `iter` points to.

`iter` : | a GSequenceIter
Returns : | the data that `iter` points to

Since 2.14

### g_sequence_set ()

    void                g_sequence_set                      (GSequenceIter *iter,
                                                             gpointer data);

Changes the data for the item pointed to by `iter` to be `data`. If the sequence has a data destroy function associated with it, that function is called on the existing data that `iter` pointed to.

`iter` : | a GSequenceIter
`data` : | new data for the item

Since 2.14

### g_sequence_iter_is_begin ()

    gboolean            g_sequence_iter_is_begin            (GSequenceIter *iter);

Returns whether `iter` is the begin iterator

`iter` : | a GSequenceIter
Returns : | whether `iter` is the begin iterator

Since 2.14

### g_sequence_iter_is_end ()

    gboolean            g_sequence_iter_is_end              (GSequenceIter *iter);

Returns whether `iter` is the end iterator

`iter` : | a GSequenceIter
Returns : | Whether `iter` is the end iterator.

Since 2.14

### g_sequence_iter_next ()

    GSequenceIter *     g_sequence_iter_next                (GSequenceIter *iter);

Returns an iterator pointing to the next position after `iter`. If `iter` is the end iterator, the end iterator is returned.

`iter` : | a GSequenceIter
Returns : | a GSequenceIter pointing to the next position after `iter`.

Since 2.14

### g_sequence_iter_prev ()

    GSequenceIter *     g_sequence_iter_prev                (GSequenceIter *iter);

Returns an iterator pointing to the previous position before `iter`. If `iter` is the begin iterator, the begin iterator is returned.

`iter` : | a GSequenceIter
Returns : | a GSequenceIter pointing to the previous position before `iter`.

Since 2.14

### g_sequence_iter_get_position ()

    gint                g_sequence_iter_get_position        (GSequenceIter *iter);

Returns the position of `iter`

`iter` : | a GSequenceIter
Returns : | the position of `iter`

Since 2.14

### g_sequence_iter_move ()

    GSequenceIter *     g_sequence_iter_move                (GSequenceIter *iter,
                                                             gint delta);

Returns the GSequenceIter which is `delta` positions away from `iter`. If `iter` is closer than -`delta` positions to the beginning of the sequence, the begin iterator is returned. If `iter` is closer than `delta` positions to the end of the sequence, the end iterator is returned.

`iter` : | a GSequenceIter
`delta` : | A positive or negative number indicating how many positions away from `iter` the returned GSequenceIter will be.
Returns : | a GSequenceIter which is `delta` positions away from `iter`.

Since 2.14

### g_sequence_iter_get_sequence ()

    GSequence *         g_sequence_iter_get_sequence        (GSequenceIter *iter);

Returns the GSequence that `iter` points into.

`iter` : | a GSequenceIter
Returns : | the GSequence that `iter` points into.

Since 2.14

### g_sequence_iter_compare ()

    gint                g_sequence_iter_compare             (GSequenceIter *a,
                                                             GSequenceIter *b);

Returns a negative number if `a` comes before `b`, 0 if they are equal, and a positive number if `a` comes after `b`.

The `a` and `b` iterators must point into the same sequence.

`a` : | a GSequenceIter
`b` : | a GSequenceIter
Returns : | A negative number if `a` comes before `b`, 0 if they are equal, and a positive number if `a` comes after `b`.

Since 2.14

### g_sequence_range_get_midpoint ()

    GSequenceIter *     g_sequence_range_get_midpoint       (GSequenceIter *begin,
                                                             GSequenceIter *end);

Finds an iterator somewhere in the range (`begin`, `end`). This iterator will be close to the middle of the range, but is not guaranteed to be exactly in the middle.

The `begin` and `end` iterators must both point to the same sequence and `begin` must come before or be equal to `end` in the sequence.

`begin` : | a GSequenceIter
`end` : | a GSequenceIter
Returns : | A GSequenceIter pointing somewhere in the (`begin`, `end`) range.

Since 2.14