description

# List<E> class abstract interface

An indexable collection of objects with a length.

Subclasses of this class implement different kinds of lists. The most common kinds of lists are:

- Fixed-length list

  An error occurs when attempting to use operations that can change the length of the list.

- Growable list

  Full implementation of the API defined in this class.

The default growable list, as created by `[]`, keeps an internal buffer, and grows that buffer when necessary. This guarantees that a sequence of add operations will each execute in amortized constant time. Setting the length directly may take time proportional to the new length, and may change the internal capacity so that a following add operation will need to immediately increase the buffer capacity. Other list implementations may have different performance behavior.

Example of fixed-length list:

    final fixedLengthList = List<int>.filled(5, 0); // Creates fixed-length list.
    print(fixedLengthList); // [0, 0, 0, 0, 0]
    fixedLengthList[0] = 87;
    fixedLengthList.setAll(1, [1, 2, 3]);
    print(fixedLengthList); // [87, 1, 2, 3, 0]
    // Fixed length list length can't be changed or increased
    fixedLengthList.length = 0;  // Throws
    fixedLengthList.add(499);    // Throws

Example of growable list:

    final growableList = <String>['A', 'B']; // Creates growable list.

To add data to the growable list, use operator[]=, add or addAll.

    growableList[0] = 'G';
    print(growableList); // [G, B]
    growableList.add('X');
    growableList.addAll({'C', 'B'});
    print(growableList); // [G, B, X, C, B]

To check whether, and where, the element is in the list, use indexOf or lastIndexOf.

    final indexA = growableList.indexOf('A'); // -1 (not in the list)
    final firstIndexB = growableList.indexOf('B'); // 1
    final lastIndexB = growableList.lastIndexOf('B'); // 4

To remove an element from the growable list, use remove, removeAt, removeLast, removeRange or removeWhere.

    growableList.remove('C');
    growableList.removeLast();
    print(growableList); // [G, B, X]

To insert an element at position in the list, use insert or insertAll.

    growableList.insert(1, 'New');
    print(growableList); // [G, New, B, X]

To replace a range of elements in the list, use fillRange, replaceRange or setRange.

    growableList.replaceRange(0, 2, ['AB', 'A']);
    print(growableList); // [AB, A, B, X]
    growableList.fillRange(2, 4, 'F');
    print(growableList); // [AB, A, F, F]

To sort the elements of the list, use sort.

    growableList.sort((a, b) => a.compareTo(b));
    print(growableList); // [A, AB, F, F]

To shuffle the elements of this list randomly, use shuffle.

    growableList.shuffle();
    print(growableList); // e.g. [AB, F, A, F]

To find the first element satisfying some predicate, or give a default value if none do, use firstWhere.

    bool isVowel(String char) => char.length == 1 && "AEIOU".contains(char);
    final firstVowel = growableList.firstWhere(isVowel, orElse: () => ''); // ''

There are similar lastWhere and singleWhere methods.

A list is an Iterable and supports all its methods, including where, map, whereType and toList.

Lists are Iterable. Iteration occurs over values in index order. Changing the values does not affect iteration, but changing the valid indices—that is, changing the list's length—between iteration steps causes a ConcurrentModificationError. This means that only growable lists can throw ConcurrentModificationError. If the length changes temporarily and is restored before continuing the iteration, the iterator might not detect it.

It is generally not allowed to modify the list's length (adding or removing elements) while an operation on the list is being performed, for example during a call to forEach or sort. Changing the list's length while it is being iterated, either by iterating it directly or through iterating an Iterable that is backed by the list, will break the iteration.

Implemented types
  - Iterable<E>
Implementers
  - DomRectList
  - DomStringList
  - FileList
  - HtmlCollection
  - ImmutableListMixin
  - LengthList
  - ListBase
  - MimeTypeArray
  - NodeList
  - NumberList
  - PluginArray
  - SourceBufferList
  - SpeechGrammarList
  - StringList
  - TextTrackCueList
  - TextTrackList
  - TouchList
  - TransformList
  - TypedDataList
  - UnmodifiableListView
Available extensions
  - EnumByName
  - FutureIterable
  - IterableExtensions
  - IterableToJSIterable
  - ListToJSArray
  - NullableIterableExtensions

## Constructors

List.empty({bool growable = false})
  Creates a new empty list.
  factory
List.filled(int length, E fill, {bool growable = false})
  Creates a list of the given length with `fill` at each position.
  factory
List.from(Iterable elements, {bool growable = true})
  Creates a list containing all `elements`.
  factory
List.generate(int length, E generator(int index), {bool growable = true})
  Generates a list of values.
  factory
List.of(Iterable<E> elements, {bool growable = true})
  Creates a list from `elements`.
  factory
List.unmodifiable(Iterable elements)
  Creates an unmodifiable list containing all `elements`.
  factory

## Properties

first ↔ E
  The first element.
  getter/setter pairinherited-getter
firstOrNull → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The first element of this iterator, or `null` if the iterable is empty.
  no setter
hashCode → int
  The hash code for this object.
  no setterinherited
indexed → Iterable<(int, T)>

  Available on Iterable<T>, provided by the IterableExtensions extension

  Pairs of elements of the indices and elements of this iterable.
  no setter
isEmpty → bool
  Whether this collection has no elements.
  no setterinherited
isNotEmpty → bool
  Whether this collection has at least one element.
  no setterinherited
iterator → Iterator<E>
  A new `Iterator` that allows iterating the elements of this `Iterable`.
  no setterinherited
last ↔ E
  The last element.
  getter/setter pairinherited-getter
lastOrNull → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The last element of this iterable, or `null` if the iterable is empty.
  no setter
length ↔ int
  The number of objects in this list.
  getter/setter pairoverride-getter
nonNulls → Iterable<T>

  Available on Iterable<T?>, provided by the NullableIterableExtensions extension

  The non-`null` elements of this iterable.
  no setter
reversed → Iterable<E>
  An Iterable of the objects in this list in reverse order.
  no setter
runtimeType → Type
  A representation of the runtime type of the object.
  no setterinherited
single → E
  Checks that this iterable has only one element, and returns that element.
  no setterinherited
singleOrNull → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The single element of this iterator, or `null`.
  no setter
toJS → JSArray<T>

  Available on List<T>, provided by the ListToJSArray extension

  Converts this List to a JSArray by either casting, unwrapping, or cloning the List.
  no setter
toJSIterable → JSIterable<T>

  Available on Iterable<T>, provided by the IterableToJSIterable extension

  A JSIterable wrapper that proxies to the Dart iterable API.
  no setter
toJSProxyOrRef → JSArray<T>

  Available on List<T>, provided by the ListToJSArray extension

  Converts this List to a JSArray by either casting, unwrapping, or proxying the List.
  no setter
wait → Future<List<T>>

  Available on Iterable<Future<T>>, provided by the FutureIterable extension

  Waits for futures in parallel.
  no setter

## Methods

add(E value) → void
  Adds `value` to the end of this list, extending the length by one.
addAll(Iterable<E> iterable) → void
  Appends all objects of `iterable` to the end of this list.
any(bool test(E element)) → bool
  Checks whether any element of this iterable satisfies `test`.
  inherited
asMap() → Map<int, E>
  An unmodifiable Map view of this list.
asNameMap() → Map<String, T>

  Available on Iterable<T>, provided by the EnumByName extension

  Creates a map from the names of enum values to the values.
byName(String name) → T

  Available on Iterable<T>, provided by the EnumByName extension

  Finds the enum value in this list with name `name`.
cast<R>() → List<R>
  Returns a view of this list as a list of `R` instances.
  override
clear() → void
  Removes all objects from this list; the length of the list becomes zero.
contains(Object? element) → bool
  Whether the collection contains an element equal to `element`.
  inherited
elementAt(int index) → E
  Returns the `index`th element.
  inherited
elementAtOrNull(int index) → T?

  Available on Iterable<T>, provided by the IterableExtensions extension

  The element at position `index` of this iterable, or `null`.
every(bool test(E element)) → bool
  Checks whether every element of this iterable satisfies `test`.
  inherited
expand<T>(Iterable<T> toElements(E element)) → Iterable<T>
  Expands each element of this Iterable into zero or more elements.
  inherited
fillRange(int start, int end, [E? fillValue]) → void
  Overwrites a range of elements with `fillValue`.
firstWhere(bool test(E element), {E orElse()?}) → E
  The first element that satisfies the given predicate `test`.
  inherited
fold<T>(T initialValue, T combine(T previousValue, E element)) → T
  Reduces a collection to a single value by iteratively combining each element of the collection with an existing value
  inherited
followedBy(Iterable<E> other) → Iterable<E>
  Creates the lazy concatenation of this iterable and `other`.
  inherited
forEach(void action(E value)) → void
  Invokes `action` on each element of this iterable in iteration order.
  inherited
getRange(int start, int end) → Iterable<E>
  Creates an Iterable that iterates over a range of elements.
indexOf(E element, [int start = 0]) → int
  The first index of `element` in this list.
indexWhere(bool test(E element), [int start = 0]) → int
  The first index in the list that satisfies the provided `test`.
insert(int index, E element) → void
  Inserts `element` at position `index` in this list.
insertAll(int index, Iterable<E> iterable) → void
  Inserts all objects of `iterable` at position `index` in this list.
join([String separator = ""]) → String
  Converts each element to a String and concatenates the strings.
  inherited
lastIndexOf(E element, [int? start]) → int
  The last index of `element` in this list.
lastIndexWhere(bool test(E element), [int? start]) → int
  The last index in the list that satisfies the provided `test`.
lastWhere(bool test(E element), {E orElse()?}) → E
  The last element that satisfies the given predicate `test`.
  inherited
map<T>(T toElement(E e)) → Iterable<T>
  The current elements of this iterable modified by `toElement`.
  inherited
noSuchMethod(Invocation invocation) → dynamic
  Invoked when a nonexistent method or property is accessed.
  inherited
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.
  inherited
remove(Object? value) → bool
  Removes the first occurrence of `value` from this list.
removeAt(int index) → E
  Removes the object at position `index` from this list.
removeLast() → E
  Removes and returns the last object in this list.
removeRange(int start, int end) → void
  Removes a range of elements from the list.
removeWhere(bool test(E element)) → void
  Removes all objects from this list that satisfy `test`.
replaceRange(int start, int end, Iterable<E> replacements) → void
  Replaces a range of elements with the elements of `replacements`.
retainWhere(bool test(E element)) → void
  Removes all objects from this list that fail to satisfy `test`.
setAll(int index, Iterable<E> iterable) → void
  Overwrites elements with the objects of `iterable`.
setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]) → void
  Writes some elements of `iterable` into a range of this list.
shuffle([Random? random]) → void
  Shuffles the elements of this list randomly.
singleWhere(bool test(E element), {E orElse()?}) → E
  The single element that satisfies `test`.
  inherited
skip(int count) → Iterable<E>
  Creates an Iterable that provides all but the first `count` elements.
  inherited
skipWhile(bool test(E element)) → Iterable<E>
  Creates an `Iterable` that skips leading elements while `test` is satisfied.
  inherited
sort([int compare(E a, E b)?]) → void
  Sorts this list according to the order specified by the `compare` function.
sublist(int start, [int? end]) → List<E>
  Returns a new list containing the elements between `start` and `end`.
take(int count) → Iterable<E>
  Creates a lazy iterable of the `count` first elements of this iterable.
  inherited
takeWhile(bool test(E element)) → Iterable<E>
  Creates a lazy iterable of the leading elements satisfying `test`.
  inherited
toList({bool growable = true}) → List<E>
  Creates a List containing the elements of this Iterable.
  inherited
toSet() → Set<E>
  Creates a Set containing the same elements as this iterable.
  inherited
toString() → String
  A string representation of this object.
  inherited
where(bool test(E element)) → Iterable<E>
  Creates a new lazy Iterable with all elements that satisfy the predicate `test`.
  inherited
whereType<T>() → Iterable<T>
  Creates a new lazy Iterable with all elements that have type `T`.
  inherited

## Operators

operator +(List<E> other) → List<E>
  Returns the concatenation of this list and `other`.
operator ==(Object other) → bool
  Whether this list is equal to `other`.
  override
operator [](int index) → E
  The object at the given `index` in the list.
operator []=(int index, E value) → void
  Sets the value at the given `index` in the list to `value`.

## Static Methods

castFrom<S, T>(List<S> source) → List<T>
  Adapts `source` to be a `List<T>`.
  override
copyRange<T>(List<T> target, int at, List<T> source, [int? start, int? end]) → void
  Copy a range of one list into another list.
writeIterable<T>(List<T> target, int at, Iterable<T> source) → void
  Write the elements of an iterable into a list.