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/* iterator.vala
*
* Copyright (C) 2007-2008 Jürg Billeter
* Copyright (C) 2009 Didier Villevalois, Maciej Piechotka
* Copyright (C) 2010-2011 Maciej Piechotka
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Author:
* Jürg Billeter <j@bitron.ch>
* Maciej Piechotka <uzytkownik2@gmail.com>
* Didier 'Ptitjes Villevalois <ptitjes@free.fr>
*/
/**
* An iterator over a collection.
*
* Gee's iterators are "on-track" iterators. They always point to an item
* except before the first call to {@link next}, or, when an
* item has been removed, until the next call to {@link next}.
*
* Please note that when the iterator is out of track, neither {@link get} nor
* {@link remove} are defined and both will fail. After the next call to
* {@link next}, they will be defined again.
*/
public interface Gee.Iterator<G> : Object, Traversable<G> {
/**
* Advances to the next element in the iteration.
*
* @return ``true`` if the iterator has a next element
*/
public abstract bool next ();
/**
* Checks whether there is a next element in the iteration.
*
* @return ``true`` if the iterator has a next element
*/
public abstract bool has_next ();
/**
* Returns the current element in the iteration.
*
* @return the current element in the iteration
*/
public abstract G get ();
/**
* Removes the current element in the iteration. The cursor is set in an
* in-between state. Both {@link get} and {@link remove} will fail until
* the next move of the cursor (calling {@link next}).
*/
public abstract void remove ();
/**
* Determines wheather the call to {@link get} is legal. It is false at the
* beginning and after {@link remove} call and true otherwise.
*/
public abstract bool valid { get; }
/**
* Determines wheather the call to {@link remove} is legal assuming the
* iterator is valid. The value must not change in runtime hence the user
* of iterator may cache it.
*/
public abstract bool read_only { get; }
/**
* Create iterator from unfolding function. The lazy value is
* force-evaluated before progressing to next element.
*
* @param f Unfolding function
* @param current If iterator is to be valid it contains the current value of it
*/
public static Iterator<A> unfold<A> (owned UnfoldFunc<A> f, owned Lazy<G>? current = null) {
return new UnfoldIterator<A> ((owned) f, (owned) current);
}
/**
* Concatinate iterators.
*
* @param iters Iterators of iterators
* @return Iterator containg values of each iterator
*/
public static Iterator<G> concat<G> (Iterator<Iterator<G>> iters) {
Iterator<G>? current = null;
if (iters.valid)
current = iters.get ();
return unfold<G> (() => {
while (true) {
if (current == null) {
if (iters.next ()) {
current = iters.get ();
} else {
return null;
}
} else if (current.next ()) {
return new Lazy<G>.from_value (current.get ());
} else {
current = null;
}
}
});
}
}
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