| // Copyright 2013 The Flutter Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| /// A [map] function that calls the function with an enumeration as well as the |
| /// value. |
| Iterable<U> indexMap<T, U>( |
| Iterable<T> iterable, U Function(int index, T value) func) sync* { |
| int index = 0; |
| for (final T value in iterable) { |
| yield func(index, value); |
| ++index; |
| } |
| } |
| |
| /// Performs like [forEach] but invokes [func] with an enumeration. |
| void enumerate<T>(Iterable<T> iterable, void Function(int, T) func) { |
| int count = 0; |
| for (final T value in iterable) { |
| func(count, value); |
| ++count; |
| } |
| } |
| |
| /// A [map] function that takes in 2 iterables. The [Iterable]s must be of |
| /// equal length. |
| Iterable<V> map2<T, U, V>( |
| Iterable<T> ts, Iterable<U> us, V Function(T t, U u) func) sync* { |
| final Iterator<T> itt = ts.iterator; |
| final Iterator<U> itu = us.iterator; |
| while (itu.moveNext() && itt.moveNext()) { |
| yield func(itt.current, itu.current); |
| } |
| if (itu.moveNext() || itt.moveNext()) { |
| throw ArgumentError('Iterables aren\'t of equal length.'); |
| } |
| } |
| |
| /// A [map] function that takes in 3 iterables. The [Iterable]s must be of |
| /// equal length. |
| Iterable<V> map3<T, U, V, W>(Iterable<T> ts, Iterable<U> us, Iterable<W> ws, |
| V Function(T t, U u, W w) func) sync* { |
| final Iterator<T> itt = ts.iterator; |
| final Iterator<U> itu = us.iterator; |
| final Iterator<W> itw = ws.iterator; |
| while (itu.moveNext() && itt.moveNext() && itw.moveNext()) { |
| yield func(itt.current, itu.current, itw.current); |
| } |
| if (itu.moveNext() || itt.moveNext() || itw.moveNext()) { |
| throw ArgumentError('Iterables aren\'t of equal length.'); |
| } |
| } |
| |
| /// Adds [value] to the end of [ts]. |
| Iterable<T> followedByOne<T>(Iterable<T> ts, T value) sync* { |
| for (final T item in ts) { |
| yield item; |
| } |
| yield value; |
| } |
| |
| Iterable<int> _count() sync* { |
| int x = 0; |
| while (true) { |
| yield x++; |
| } |
| } |
| |
| /// All integers starting at zero. |
| final Iterable<int> wholeNumbers = _count(); |
| |
| /// Repeats an [item] [n] times. |
| Iterable<T> repeat<T>(T item, int n) sync* { |
| for (int i = 0; i < n; ++i) { |
| yield item; |
| } |
| } |