Iterable<E> class

A collection of values, or "elements", that can be accessed sequentially.

A collection of values, or "elements", that can be accessed sequentially.

The elements of the iterable are accessed by getting an Iterator using the iterator getter, and using it to step through the values. Stepping with the iterator is done by calling Iterator.moveNext, and if the call returns true, the iterator has now moved to the next element, which is then available as Iterator.current. If the call returns false, there are no more elements, and iterator.currrent returns null.

You can create more than one iterator from the same Iterable. Each time iterator is read, it returns a new iterator, and different iterators can be stepped through independently, each giving access to all the elements of the iterable. The iterators of the same iterable should provide the same values in the same order (unless the underlying collection is modified between the iterations, which some collections allow).

You can also iterate over the elements of an Iterable using the for-in loop construct, which uses the iterator getter behind the scenes. For example, you can iterate over all of the keys of a Map, because Map keys are iterable.

Map kidsBooks = {'Matilda': 'Roald Dahl',
                 'Green Eggs and Ham': 'Dr Seuss',
                 'Where the Wild Things Are': 'Maurice Sendak'};
for (var book in kidsBooks.keys) {
  print('$book was written by ${kidsBooks[book]}');
}

The List and Set classes are both Iterable, as are most classes in the dart:collection library.

Some Iterable collections can be modified. Adding an element to a List or Set will change which elements it contains, and adding a new key to a Map changes the elements of Map.keys. Iterators created after the change will provide the new elements, and may or may not preserve the order of existing elements (for example, a HashSet may completely change its order when a single element is added).

Changing a collection while it is being iterated is generally not allowed. Doing so will break the iteration, which is typically signalled by throwing a ConcurrentModificationError the next time Iterator.moveNext is called. The current value of Iterator.current getter should not be affected by the change in the collection, the current value was set by the previous call to Iterator.moveNext.

Some iterables compute their elements dynamically every time they are iterated, like the one returned by Iterable.generate or the iterable returned by a sync* generator function. If the computation doesn't depend on other objects that may change, then the generated sequence should be the same one every time it's iterated.

The members of Iterable, other than iterator itself, work by looking at the elements of the iterable. This can be implemented by running through the iterator, but some classes may have more efficient ways of finding the result (like last or length on a List, or contains on a Set).

The methods that return another Iterable (like map and where) are all lazy - they will iterate the original (as necessary) every time the returned iterable is iterated, and not before.

Since an iterable may be iterated more than once, it's not recommended to have detectable side-effects in the iterator. For methods like map and while, the returned iterable will execute the argument function on every iteration, so those functions should also not have side effects.

Implementors

Constructors

Iterable ( )
const
Iterable.generate ( int count, [E generator(int index)] )
Creates an Iterable that generates its elements dynamically.
Iterable.empty ( )
const
Creates an empty iterable.

Instance Properties

iterator Iterator<E>
read-only
length int
read-only
isEmpty bool
read-only
isNotEmpty bool
read-only
first E
read-only
last E
read-only
single E
read-only

Instance Methods

map ( dynamic f(E element) ) → Iterable
Returns a new lazy Iterable with elements that are created by calling f on each element of this Iterable in iteration order.
where ( bool f(E element) ) → Iterable<E>
Returns a new lazy Iterable with all elements that satisfy the predicate test.
expand ( Iterable f(E element) ) → Iterable
Expands each element of this Iterableinto zero or more elements.
contains ( Object element ) → bool
Returns true if the collection contains an element equal to element.
forEach ( void f(E element) ) → void
Applies the function f to each element of this collection in iteration order.
reduce ( E combine(E value, E element) ) → E
Reduces a collection to a single value by iteratively combining elements of the collection using the provided function.
fold ( initialValue, dynamic combine(previousValue, E element) ) → dynamic
Reduces a collection to a single value by iteratively combining each element of the collection with an existing value
every ( bool f(E element) ) → bool
Checks whether every element of this iterable satisfies test.
join ( [String separator = ""] ) → String
Converts each element to a String and concatenates the strings.
any ( bool f(E element) ) → bool
Checks whether any element of this iterable satisfies test.
toList ( {bool growable: true} ) → List<E>
Creates a List containing the elements of this Iterable.
toSet ( ) → Set<E>
Creates a Set containing the same elements as this iterable.
take ( int n ) → Iterable<E>
Returns a lazy iterable of the count first elements of this iterable.
takeWhile ( bool test(E value) ) → Iterable<E>
Returns a lazy iterable of the leading elements satisfying test.
skip ( int n ) → Iterable<E>
Returns an Iterable that provides all but the first count elements.
skipWhile ( bool test(E value) ) → Iterable<E>
Returns an Iterable that skips leading elements while test is satisfied.
firstWhere ( bool test(E element), {E orElse()} ) → E
Returns the first element that satisfies the given predicate test.
lastWhere ( bool test(E element), {E orElse()} ) → E
Returns the last element that satisfies the given predicate test.
singleWhere ( bool test(E element) ) → E
Returns the single element that satisfies test.
elementAt ( int index ) → E
Returns the indexth element.
toString ( ) → String
Returns a string representation of (some of) the elements of this.