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Unified Diff: sdk/lib/_collection_dev/list.dart

Issue 12262037: Make List.skip, List.take and List.reversed return Iterables, not Lists. (Closed) Base URL: https://dart.googlecode.com/svn/branches/bleeding_edge/dart
Patch Set: Address comments, small fixes. Created 7 years, 10 months ago
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Index: sdk/lib/_collection_dev/list.dart
diff --git a/sdk/lib/_collection_dev/list.dart b/sdk/lib/_collection_dev/list.dart
index 7af0fbbe6f773a68bfea405f75adcc3140ffc9da..0260290dc1dd423987a17037d675354d6c6f9024 100644
--- a/sdk/lib/_collection_dev/list.dart
+++ b/sdk/lib/_collection_dev/list.dart
@@ -101,23 +101,23 @@ abstract class ListBase<E> extends Collection<E> implements List<E> {
return new MappedList(this, f);
}
- List<E> take(int n) {
- return new ListView(this, 0, n);
+ Iterable<E> take(int n) {
+ return new SubListIterable(this, 0, n);
}
- List<E> skip(int n) {
- return new ListView(this, n, null);
+ Iterable<E> skip(int n) {
+ return new SubListIterable(this, n, null);
}
- String toString() => ToString.collectionToString(this);
+ Iterable<E> get reversed => new ReversedListIterable(this);
- List<E> get reversed {
- return new ReversedListView(this, 0, null);
- }
+ String toString() => ToString.collectionToString(this);
}
/**
* Abstract class implementing the non-length changing operations of [List].
+ *
+ * All modifications are performed using [[]=].
*/
abstract class FixedLengthListBase<E> extends ListBase<E> {
void operator[]=(int index, E value);
@@ -286,35 +286,6 @@ abstract class UnmodifiableListBase<E> extends ListBase<E> {
}
}
-/**
- * Iterates over a [List] in growing index order.
- */
-class ListIterator<E> implements Iterator<E> {
- final List<E> _list;
- final int _length;
- int _position;
- E _current;
-
- ListIterator(List<E> list)
- : _list = list, _position = -1, _length = list.length;
-
- bool moveNext() {
- if (_list.length != _length) {
- throw new ConcurrentModificationError(_list);
- }
- int nextPosition = _position + 1;
- if (nextPosition < _length) {
- _position = nextPosition;
- _current = _list[nextPosition];
- return true;
- }
- _current = null;
- return false;
- }
-
- E get current => _current;
-}
-
class MappedList<S, T> extends UnmodifiableListBase<T> {
final List<S> _list;
// TODO(ahe): Restore type when feature is implemented in dart2js
@@ -332,218 +303,17 @@ class EmptyList<E> extends FixedLengthListBase<E> {
int get length => 0;
E operator[](int index) { throw new RangeError.value(index); }
void operator []=(int index, E value) { throw new RangeError.value(index); }
- List<E> skip(int count) => this;
- List<E> take(int count) => this;
- List<E> get reversed => this;
+ Iterable<E> skip(int count) => const EmptyIterable();
+ Iterable<E> take(int count) => const EmptyIterable();
+ Iterable<E> get reversed => const EmptyIterable();
void sort([int compare(E a, E b)]) {}
}
-/**
- * A fixed-length view of a sub-range of another [List].
- *
- * The range is described by start and end points relative
- * to the other List's start or end.
- *
- * The range changes dynamically as the underlying list changes
- * its length.
- */
-abstract class SubListView<E> extends UnmodifiableListBase<E> {
- final List<E> _list;
- final int _start;
- final int _end;
-
- /**
- * Create a sub-list view.
- *
- * Both [_start] and [_end] can be given as positions
- * relative to the start of [_list] (a non-negative integer)
- * or relative to the end of [_list] (a negative integer or
- * null, with null being at the end of the list).
- */
- SubListView(this._list, this._start, this._end);
-
- int _absoluteIndex(int relativeIndex) {
- if (relativeIndex == null) return _list.length;
- if (relativeIndex < 0) {
- int result = _list.length + relativeIndex;
- if (result < 0) return 0;
- return result;
- }
- if (relativeIndex > _list.length) {
- return _list.length;
- }
- return relativeIndex;
- }
-
- int get length {
- int result = _absoluteIndex(_end) - _absoluteIndex(_start);
- if (result >= 0) return result;
- return 0;
- }
-
- _createListView(int start, int end) {
- if (start == null) return new EmptyList<E>();
- if (end != null) {
- if (start < 0) {
- if (end <= start) return new EmptyList<E>();
- } else {
- if (end >= 0 && end <= start) return new EmptyList<E>();
- }
- }
- return new ListView(_list, start, end);
- }
-
- _createReversedListView(int start, int end) {
- if (start == null) return new EmptyList<E>();
- if (end != null) {
- if (start < 0) {
- if (end <= start) return new EmptyList<E>();
- } else {
- if (end >= 0 && end <= start) return new EmptyList<E>();
- }
- }
- return new ReversedListView(_list, start, end);
- }
-}
-
-
-/**
- * A fixed-length view of a sub-range of a [List].
- */
-class ListView<E> extends SubListView<E> {
-
- ListView(List<E> list, int start, int end) : super(list, start, end);
-
- E operator[](int index) {
- int start = _absoluteIndex(_start);
- int end = _absoluteIndex(_end);
- int length = end - start;
- if (index < 0 || index >= length) {
- throw new RangeError.range(index, 0, length);
- }
- return _list[start + index];
- }
-
- List<E> skip(int count) {
- if (count is! int || count < 0) {
- throw new ArgumentError(count);
- }
- if (_start == null) {
- return new EmptyList<E>();
- }
- int newStart = _start + count;
- if (_start < 0 && newStart >= 0) {
- return new EmptyList<E>();
- }
- return _createListView(newStart, _end);
- }
-
- List<E> take(int count) {
- if (count is! int || count < 0) {
- throw new ArgumentError(count);
- }
- if (_start == null) {
- return new EmptyList<E>();
- }
- int newEnd = _start + count;
- if (_start < 0 && newEnd >= 0) {
- newEnd = null;
- }
- return _createListView(_start, newEnd);
- }
-
- List<E> get reversed => new ReversedListView(_list, _start, _end);
-}
-
-/**
- * Reversed view of a [List], or a slice of a list.
- *
- * The view is fixed-length and becomes invalid if the underlying
- * list changes its length below the slice used by this reversed list.
- *
- * Start index and end index can be either positive, negative or null.
- * Positive means an index relative to the start of the list,
- * negative means an index relative to the end of the list, and null
- * means at the end of the list (since there is no -0 integer).
- */
-class ReversedListView<E> extends SubListView<E> {
-
- ReversedListView(List<E> list, int start, int end)
- : super(list, start, end);
-
- E operator[](int index) {
- int start = _absoluteIndex(_start);
- int end = _absoluteIndex(_end);
- int length = end - start;
- if (index < 0 || index >= length) {
- throw new RangeError.range(index, 0, length);
- }
- return _list[end - index - 1];
- }
-
- List<E> skip(int count) {
- if (count is! int || count < 0) {
- throw new ArgumentError(count);
- }
- if (_end == null) {
- return _createReversedListView(_start, -count);
- }
- int newEnd = _end - count;
- if (_end >= 0 && newEnd < 0) {
- return new EmptyList<E>();
- }
- return _createReversedListView(_start, newEnd);
- }
-
- List<E> take(int count) {
- if (count is! int || count < 0) {
- throw new ArgumentError(count);
- }
- int newStart;
- if (_end == null) {
- newStart = -count;
- } else {
- newStart = _end - count;
- if (_end >= 0 && newStart < 0) {
- return new EmptyList<E>();
- }
- }
- return _createReversedListView(newStart, _end);
- }
+class ReversedListIterable<E> extends ListIterable<E> {
+ Iterable<E> _source;
+ ReversedListIterable(this._source);
- Iterator<E> get iterator => new ReverseListIterator<E>(
- _list, _absoluteIndex(_start), _absoluteIndex(_end));
-
- List<E> get reversed {
- return new ListView(_list, _start, _end);
- }
-}
-
-/**
- * An [Iterator] over a slice of a list that access elements in reverse order.
- */
-class ReverseListIterator<E> implements Iterator<E> {
- final List<E> _list;
- final int _start;
- final int _originalLength;
- int _index;
- E _current;
-
- ReverseListIterator(List<E> list, int start, int end)
- : _list = list,
- _start = start,
- _index = end,
- _originalLength = list.length;
-
- bool moveNext() {
- if (_list.length != _originalLength) {
- throw new ConcurrentModificationError(_list);
- }
- if (_index <= _start) return false;
- _index -= 1;
- _current = _list[_index];
- return true;
- }
+ int get length => _source.length;
- E get current => _current;
+ E elementAt(int index) => _source.elementAt(_source.length - 1 - index);
}
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