List<E> 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.

Constructors#

List.empty() factory#

Creates a new empty list.

If growable is false, which is the default, the list is a fixed-length list of length zero. If growable is true, the list is growable and equivalent to <E>[].

final growableList = List.empty(growable: true); // []
growableList.add(1); // [1]

final fixedLengthList = List.empty(growable: false);
fixedLengthList.add(1); // error

external factory List.empty({bool growable = false});

List.filled() factory#

Creates a list of the given length with fill at each position.

The length must be a non-negative integer.

Example:

final zeroList = List<int>.filled(3, 0, growable: true); // [0, 0, 0]

The created list is fixed-length if growable is false (the default) and growable if growable is true. If the list is growable, increasing its length will not initialize new entries with fill. After being created and filled, the list is no different from any other growable or fixed-length list created using [] or other List constructors.

All elements of the created list share the same fill value.

final shared = List.filled(3, []);
shared[0].add(499);
print(shared);  // [[499], [499], [499]]

You can use List.generate to create a list with a fixed length and a new object at each position.

final unique = List.generate(3, (_) => []);
unique[0].add(499);
print(unique); // [[499], [], []]

external factory List.filled(int length, E fill, {bool growable = false});

List.from() factory#

Creates a list containing all elements.

The Iterator of elements provides the order of the elements.

All the elements should be instances of E.

Example:

final numbers = <num>[1, 2, 3];
final listFrom = List<int>.from(numbers);
print(listFrom); // [1, 2, 3]

The elements iterable itself may have any element type, so this constructor can be used to down-cast a List, for example as:

const jsonArray = '''
  [{"text": "foo", "value": 1, "status": true},
   {"text": "bar", "value": 2, "status": false}]
''';
final List<dynamic> dynamicList = jsonDecode(jsonArray);
final List<Map<String, dynamic>> fooData =
    List.from(dynamicList.where((x) => x is Map && x['text'] == 'foo'));
print(fooData); // [{text: foo, value: 1, status: true}]

This constructor creates a growable list when growable is true; otherwise, it returns a fixed-length list.

external factory List.from(Iterable elements, {bool growable = true});

List.generate() factory#

Generates a list of values.

Creates a list with length positions and fills it with values created by calling generator for each index in the range 0 .. length - 1 in increasing order.

final growableList =
    List<int>.generate(3, (int index) => index * index, growable: true);
print(growableList); // [0, 1, 4]

final fixedLengthList =
    List<int>.generate(3, (int index) => index * index, growable: false);
print(fixedLengthList); // [0, 1, 4]

The created list is fixed-length if growable is set to false.

The length must be non-negative.

external factory List.generate(
  int length,
  E generator(int index), {
  bool growable = true,
});

List.of() factory#

Creates a list from elements.

The Iterator of elements provides the order of the elements.

This constructor creates a growable list when growable is true; otherwise, it returns a fixed-length list.

final numbers = <int>[1, 2, 3];
final listOf = List<num>.of(numbers);
print(listOf); // [1, 2, 3]

external factory List.of(Iterable<E> elements, {bool growable = true});

List.unmodifiable() factory#

Creates an unmodifiable list containing all elements.

The Iterator of elements provides the order of the elements.

An unmodifiable list cannot have its length or elements changed. If the elements are themselves immutable, then the resulting list is also immutable.

final numbers = <int>[1, 2, 3];
final unmodifiableList = List.unmodifiable(numbers); // [1, 2, 3]
unmodifiableList[1] = 87; // Throws.

external factory List.unmodifiable(Iterable elements);

Properties#

first read / write inherited-getter#

getter:

The first element.

Throws a StateError if this is empty. Otherwise returns the first element in the iteration order, equivalent to this.elementAt(0).

setter:

The first element of the list.

The list must be non-empty when accessing its first element.

The first element of a list can be modified, unlike an Iterable. A list.first is equivalent to list[0], both for getting and setting the value.

final numbers = <int>[1, 2, 3];
print(numbers.first); // 1
numbers.first = 10;
print(numbers.first); // 10
numbers.clear();
numbers.first; // Throws.

E get first {
  Iterator<E> it = iterator;
  if (!it.moveNext()) {
    throw IterableElementError.noElement();
  }
  return it.current;
}

void set first(E value);

firstOrNull extension no setter#

The first element of this iterator, or null if the iterable is empty.

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

T? get firstOrNull {
  var iterator = this.iterator;
  if (iterator.moveNext()) return iterator.current;
  return null;
}

hashCode no setter inherited#

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

external int get hashCode;

indexed extension no setter#

Pairs of elements of the indices and elements of this iterable.

The elements are (0, this.first) through (this.length - 1, this.last), in index/iteration order.

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

@pragma('vm:prefer-inline')
Iterable<(int, T)> get indexed => IndexedIterable<T>(this, 0);

isEmpty no setter inherited#

Whether this collection has no elements.

May be computed by checking if iterator.moveNext() returns false.

Example:

final emptyList = <int>[];
print(emptyList.isEmpty); // true;
print(emptyList.iterator.moveNext()); // false

Inherited from Iterable.

bool get isEmpty => !iterator.moveNext();

isNotEmpty no setter inherited#

Whether this collection has at least one element.

May be computed by checking if iterator.moveNext() returns true.

Example:

final numbers = <int>{1, 2, 3};
print(numbers.isNotEmpty); // true;
print(numbers.iterator.moveNext()); // true

Inherited from Iterable.

bool get isNotEmpty => !isEmpty;

iterator no setter inherited#

A new Iterator that allows iterating the elements of this Iterable.

Iterable classes may specify the iteration order of their elements (for example List always iterate in index order), or they may leave it unspecified (for example a hash-based Set may iterate in any order).

Each time iterator is read, it returns a new iterator, which can be used to iterate through all the elements again. The iterators of the same iterable can be stepped through independently, but should return the same elements in the same order, as long as the underlying collection isn't changed.

Modifying the collection may cause new iterators to produce different elements, and may change the order of existing elements. A List specifies its iteration order precisely, so modifying the list changes the iteration order predictably. A hash-based Set may change its iteration order completely when adding a new element to the set.

Modifying the underlying collection after creating the new iterator may cause an error the next time Iterator.moveNext is called on that iterator. Any modifiable iterable class should specify which operations will break iteration.

Inherited from Iterable.

Iterator<E> get iterator;

last read / write inherited-getter#

getter:

The last element.

Throws a StateError if this is empty. Otherwise may iterate through the elements and returns the last one seen. Some iterables may have more efficient ways to find the last element (for example a list can directly access the last element, without iterating through the previous ones).

setter:

The last element of the list.

The list must be non-empty when accessing its last element.

The last element of a list can be modified, unlike an Iterable. A list.last is equivalent to theList[theList.length - 1], both for getting and setting the value.

final numbers = <int>[1, 2, 3];
print(numbers.last); // 3
numbers.last = 10;
print(numbers.last); // 10
numbers.clear();
numbers.last; // Throws.

E get last {
  Iterator<E> it = iterator;
  if (!it.moveNext()) {
    throw IterableElementError.noElement();
  }
  E result;
  do {
    result = it.current;
  } while (it.moveNext());
  return result;
}

void set last(E value);

lastOrNull extension no setter#

The last element of this iterable, or null if the iterable is empty.

This computation may not be efficient. The last value is potentially found by iterating the entire iterable and temporarily storing every value. The process only iterates the iterable once. If iterating more than once is not a problem, it may be more efficient for some iterables to do:

var lastOrNull = iterable.isEmpty ? null : iterable.last;

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

T? get lastOrNull {
  if (this is EfficientLengthIterable) {
    if (isEmpty) return null;
    return last;
  }
  var iterator = this.iterator;
  if (!iterator.moveNext()) return null;
  T result;
  do {
    result = iterator.current;
  } while (iterator.moveNext());
  return result;
}

length read / write override-getter#

getter:

The number of objects in this list.

The valid indices for a list are 0 through length - 1.

final numbers = <int>[1, 2, 3];
print(numbers.length); // 3

setter:

Setting the length changes the number of elements in the list.

The list must be growable. If newLength is greater than current length, new entries are initialized to null, so newLength must not be greater than the current length if the element type E is non-nullable.

final maybeNumbers = <int?>[1, null, 3];
maybeNumbers.length = 5;
print(maybeNumbers); // [1, null, 3, null, null]
maybeNumbers.length = 2;
print(maybeNumbers); // [1, null]

final numbers = <int>[1, 2, 3];
numbers.length = 1;
print(numbers); // [1]
numbers.length = 5; // Throws, cannot add `null`s.

int get length;

set length(int newLength);

nonNulls extension no setter#

The non-null elements of this iterable.

The same elements as this iterable, except that null values are omitted.

Available on Iterable<E>, provided by the NullableIterableExtensions<T extends Object> extension

Iterable<T> get nonNulls => NonNullsIterable<T>(this);

reversed no setter#

An Iterable of the objects in this list in reverse order.

final numbers = <String>['two', 'three', 'four'];
final reverseOrder = numbers.reversed;
print(reverseOrder.toList()); // [four, three, two]

Iterable<E> get reversed;

runtimeType no setter inherited#

A representation of the runtime type of the object.

Inherited from Object.

external Type get runtimeType;

single no setter inherited#

Checks that this iterable has only one element, and returns that element.

Throws a StateError if this is empty or has more than one element. This operation will not iterate past the second element.

Inherited from Iterable.

E get single {
  Iterator<E> it = iterator;
  if (!it.moveNext()) throw IterableElementError.noElement();
  E result = it.current;
  if (it.moveNext()) throw IterableElementError.tooMany();
  return result;
}

singleOrNull extension no setter#

The single element of this iterator, or null.

If the iterator has precisely one element, this is that element. Otherwise, if the iterator has zero elements, or it has two or more, the value is null.

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

T? get singleOrNull {
  var iterator = this.iterator;
  if (iterator.moveNext()) {
    var result = iterator.current;
    if (!iterator.moveNext()) return result;
  }
  return null;
}

toJS extension no setter#

Converts this List to a JSArray by either casting, unwrapping, or cloning the List.

When compiling to JavaScript, the core List is a JavaScript Array, and therefore this getter simply casts. If the List is not a core List e.g. a user-defined list, this getter throws with a cast error.

When compiling to Wasm, this List is a wrapper around an Array if it was converted via JSArrayToList.toDart. If it's a wrapper, this getter unwraps it and returns the Array. If it's instantiated in Dart, this getter clones this List's values into a new JSArray.

Avoid assuming that modifications to this List will affect the returned JSArray and vice versa in all compilers unless it was first converted via JSArrayToList.toDart.

Available on List<E>, provided by the ListToJSArray<T extends JSAny?> extension

external JSArray<T> get toJS;

toJSProxyOrRef extension no setter#

Converts this List to a JSArray by either casting, unwrapping, or proxying the List.

When compiling to JavaScript, the core List is a JavaScript Array, and therefore this getter simply casts. If the List is not a core List e.g. a user-defined list, this getter throws with a cast error.

When compiling to Wasm, this List is a wrapper around an Array if it was converted via JSArrayToList.toDart. If it's a wrapper, this getter unwraps it and returns the Array. If it's instantiated in Dart, this getter proxies the List using a heavyweight Array wrapper. Access to the original List's elements may be very unperformant.

Modifications to this List will affect the returned JSArray and vice versa.

Available on List<E>, provided by the ListToJSArray<T extends JSAny?> extension

external JSArray<T> get toJSProxyOrRef;

wait extension no setter#

Waits for futures in parallel.

Waits for all the futures in this iterable. Returns a list of the resulting values, in the same order as the futures which created them, if all futures are successful.

Similar to Future.wait, but reports errors using a ParallelWaitError, which allows the caller to handle errors and dispose successful results if necessary.

The returned future is completed when all the futures have completed. If any of the futures do not complete, nor does the returned future.

If any future completes with an error, the returned future completes with a ParallelWaitError. The ParallelWaitError.values is a list of the values for successful futures and null for futures with errors. The ParallelWaitError.errors is a list of the same length, with null values for the successful futures and an AsyncError with the error for futures which completed with an error.

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

Future<List<T>> get wait {
  var results = [for (var f in this) _FutureResult<T>(f)];
  if (results.isEmpty) return Future<List<T>>.value(<T>[]);

  @pragma('vm:awaiter-link')
  final c = Completer<List<T>>.sync();

  _FutureResult._waitAll(results, (errors) {
    if (errors == 0) {
      c.complete([for (var r in results) r.value]);
    } else {
      var errorList = [for (var r in results) r.errorOrNull];
      c.completeError(
        ParallelWaitError<List<T?>, List<AsyncError?>>(
          [for (var r in results) r.valueOrNull],
          errorList,
          errorCount: errors,
          defaultError: errorList.firstWhere(_notNull),
        ),
      );
    }
  });
  return c.future;
}

Methods#

add()#

Adds value to the end of this list, extending the length by one.

The list must be growable.

final numbers = <int>[1, 2, 3];
numbers.add(4);
print(numbers); // [1, 2, 3, 4]

void add(E value);

addAll()#

Appends all objects of iterable to the end of this list.

Extends the length of the list by the number of objects in iterable. The list must be growable.

final numbers = <int>[1, 2, 3];
numbers.addAll([4, 5, 6]);
print(numbers); // [1, 2, 3, 4, 5, 6]

void addAll(Iterable<E> iterable);

any() inherited#

Checks whether any element of this iterable satisfies test.

Checks every element in iteration order, and returns true if any of them make test return true, otherwise returns false. Returns false if the iterable is empty.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
var result = numbers.any((element) => element >= 5); // true;
result = numbers.any((element) => element >= 10); // false;

Inherited from Iterable.

bool any(bool test(E element)) {
  for (E element in this) {
    if (test(element)) return true;
  }
  return false;
}

asMap()#

An unmodifiable Map view of this list.

The map uses the indices of this list as keys and the corresponding objects as values. The Map.keys Iterable iterates the indices of this list in numerical order.

var words = <String>['fee', 'fi', 'fo', 'fum'];
var map = words.asMap();  // {0: fee, 1: fi, 2: fo, 3: fum}
map.keys.toList(); // [0, 1, 2, 3]

Map<int, E> asMap();

asNameMap() extension#

Creates a map from the names of enum values to the values.

The collection that this method is called on is expected to have enums with distinct names, like the values list of an enum class. Only one value for each name can occur in the created map, so if two or more enum values have the same name (either being the same value, or being values of different enum type), at most one of them will be represented in the returned map.

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

Map<String, T> asNameMap() => <String, T>{
  for (var value in this) value._name: value,
};

byName() extension#

Finds the enum value in this list with name name.

Goes through this collection looking for an enum with name name, as reported by EnumName.name. Returns the first value with the given name. Such a value must be found.

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

T byName(String name) {
  for (var value in this) {
    if (value._name == name) return value;
  }
  throw ArgumentError.value(name, "name", "No enum value with that name");
}

cast() override#

Returns a view of this list as a list of R instances.

If this list contains only instances of R, all read operations will work correctly. If any operation tries to read an element that is not an instance of R, the access will throw instead.

Elements added to the list (e.g., by using add or addAll) must be instances of R to be valid arguments to the adding function, and they must also be instances of E to be accepted by this list as well.

Methods which accept Object? as argument, like contains and remove, will pass the argument directly to the this list's method without any checks. That means that you can do listOfStrings.cast<int>().remove("a") successfully, even if it looks like it shouldn't have any effect.

Typically implemented as List.castFrom<E, R>(this).

List<R> cast<R>();

clear()#

Removes all objects from this list; the length of the list becomes zero.

The list must be growable.

final numbers = <int>[1, 2, 3];
numbers.clear();
print(numbers.length); // 0
print(numbers); // []

void clear();

contains() inherited#

Whether the collection contains an element equal to element.

This operation will check each element in order for being equal to element, unless it has a more efficient way to find an element equal to element. Stops iterating on the first equal element.

The equality used to determine whether element is equal to an element of the iterable defaults to the Object.== of the element.

Some types of iterable may have a different equality used for its elements. For example, a Set may have a custom equality (see Set.identity) that its contains uses. Likewise the Iterable returned by a Map.keys call should use the same equality that the Map uses for keys.

Example:

final gasPlanets = <int, String>{1: 'Jupiter', 2: 'Saturn'};
final containsOne = gasPlanets.keys.contains(1); // true
final containsFive = gasPlanets.keys.contains(5); // false
final containsJupiter = gasPlanets.values.contains('Jupiter'); // true
final containsMercury = gasPlanets.values.contains('Mercury'); // false

Inherited from Iterable.

bool contains(Object? element) {
  for (E e in this) {
    if (e == element) return true;
  }
  return false;
}

elementAt() inherited#

Returns the indexth element.

The index must be non-negative and less than length. Index zero represents the first element (so iterable.elementAt(0) is equivalent to iterable.first).

May iterate through the elements in iteration order, ignoring the first index elements and then returning the next. Some iterables may have a more efficient way to find the element.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
final elementAt = numbers.elementAt(4); // 6

Inherited from Iterable.

E elementAt(int index) {
  RangeError.checkNotNegative(index, "index");
  var iterator = this.iterator;
  var skipCount = index;
  while (iterator.moveNext()) {
    if (skipCount == 0) return iterator.current;
    skipCount--;
  }
  throw IndexError.withLength(
    index,
    index - skipCount,
    indexable: this,
    name: "index",
  );
}

elementAtOrNull() extension#

The element at position index of this iterable, or null.

The index is zero based, and must be non-negative.

Returns the result of elementAt(index) if the iterable has at least index + 1 elements, and null otherwise.

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

T? elementAtOrNull(int index) {
  RangeError.checkNotNegative(index, "index");
  if (this is EfficientLengthIterable) {
    if (index >= length) return null;
    return elementAt(index);
  }
  var iterator = this.iterator;
  do {
    if (!iterator.moveNext()) return null;
  } while (--index >= 0);
  return iterator.current;
}

every() inherited#

Checks whether every element of this iterable satisfies test.

Checks every element in iteration order, and returns false if any of them make test return false, otherwise returns true. Returns true if the iterable is empty.

Example:

final planetsByMass = <double, String>{0.06: 'Mercury', 0.81: 'Venus',
  0.11: 'Mars'};
// Checks whether all keys are smaller than 1.
final every = planetsByMass.keys.every((key) => key < 1.0); // true

Inherited from Iterable.

bool every(bool test(E element)) {
  for (E element in this) {
    if (!test(element)) return false;
  }
  return true;
}

expand() inherited#

Expands each element of this Iterable into zero or more elements.

The resulting Iterable runs through the elements returned by toElements for each element of this, in iteration order.

The returned Iterable is lazy, and calls toElements for each element of this iterable every time the returned iterable is iterated.

Example:

Iterable<int> count(int n) sync* {
  for (var i = 1; i <= n; i++) {
    yield i;
   }
 }

var numbers = [1, 3, 0, 2];
print(numbers.expand(count)); // (1, 1, 2, 3, 1, 2)

Equivalent to:

Iterable<T> expand<T>(Iterable<T> toElements(E e)) sync* {
  for (var value in this) {
    yield* toElements(value);
  }
}

Inherited from Iterable.

Iterable<T> expand<T>(Iterable<T> toElements(E element)) =>
    ExpandIterable<E, T>(this, toElements);

fillRange()#

Overwrites a range of elements with fillValue.

Sets the positions greater than or equal to start and less than end, to fillValue.

The provided range, given by start and end, must be valid. A range from start to end is valid if 0 ≤ start ≤ end ≤ length. An empty range (with end == start) is valid.

If the element type is not nullable, the fillValue must be provided and must be non-null.

Example:

final words = List.filled(5, 'old');
print(words); // [old, old, old, old, old]
words.fillRange(1, 3, 'new');
print(words); // [old, new, new, old, old]

void fillRange(int start, int end, [E? fillValue]);

firstWhere() inherited#

The first element that satisfies the given predicate test.

Iterates through elements and returns the first to satisfy test.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
var result = numbers.firstWhere((element) => element < 5); // 1
result = numbers.firstWhere((element) => element > 5); // 6
result =
    numbers.firstWhere((element) => element > 10, orElse: () => -1); // -1

If no element satisfies test, the result of invoking the orElse function is returned. If orElse is omitted, it defaults to throwing a StateError. Stops iterating on the first matching element.

Inherited from Iterable.

E firstWhere(bool test(E element), {E orElse()?}) {
  for (E element in this) {
    if (test(element)) return element;
  }
  if (orElse != null) return orElse();
  throw IterableElementError.noElement();
}

fold() inherited#

Reduces a collection to a single value by iteratively combining each element of the collection with an existing value

Uses initialValue as the initial value, then iterates through the elements and updates the value with each element using the combine function, as if by:

var value = initialValue;
for (E element in this) {
  value = combine(value, element);
}
return value;

Example of calculating the sum of an iterable:

final numbers = <double>[10, 2, 5, 0.5];
const initialValue = 100.0;
final result = numbers.fold<double>(
    initialValue, (previousValue, element) => previousValue + element);
print(result); // 117.5

Inherited from Iterable.

T fold<T>(T initialValue, T combine(T previousValue, E element)) {
  var value = initialValue;
  for (E element in this) value = combine(value, element);
  return value;
}

followedBy() inherited#

Creates the lazy concatenation of this iterable and other.

The returned iterable will provide the same elements as this iterable, and, after that, the elements of other, in the same order as in the original iterables.

Example:

var planets = <String>['Earth', 'Jupiter'];
var updated = planets.followedBy(['Mars', 'Venus']);
print(updated); // (Earth, Jupiter, Mars, Venus)

Inherited from Iterable.

Iterable<E> followedBy(Iterable<E> other) {
  var self = this; &#47;&#47; TODO(lrn): Remove when we can promote `this`.
  if (self is EfficientLengthIterable<E>) {
    return FollowedByIterable<E>.firstEfficient(self, other);
  }
  return FollowedByIterable<E>(this, other);
}

forEach() inherited#

Invokes action on each element of this iterable in iteration order.

Example:

final numbers = <int>[1, 2, 6, 7];
numbers.forEach(print);
// 1
// 2
// 6
// 7

Inherited from Iterable.

void forEach(void action(E element)) {
  for (E element in this) action(element);
}

getRange()#

Creates an Iterable that iterates over a range of elements.

The returned iterable iterates over the elements of this list with positions greater than or equal to start and less than end.

The provided range, start and end, must be valid at the time of the call. A range from start to end is valid if 0 ≤ start ≤ end ≤ length. An empty range (with end == start) is valid.

The returned Iterable behaves like skip(start).take(end - start). That is, it does not break if this list changes size, it just ends early if it reaches the end of the list early (if end, or even start, becomes greater than length).

final colors = <String>['red', 'green', 'blue', 'orange', 'pink'];
final firstRange = colors.getRange(0, 3);
print(firstRange.join(', ')); // red, green, blue

final secondRange = colors.getRange(2, 5);
print(secondRange.join(', ')); // blue, orange, pink

Iterable<E> getRange(int start, int end);

indexOf()#

The first index of element in this list.

Searches the list from index start to the end of the list. The first time an object o is encountered so that o == element, the index of o is returned.

final notes = <String>['do', 're', 'mi', 're'];
print(notes.indexOf('re')); // 1

final indexWithStart = notes.indexOf('re', 2); // 3

Returns -1 if element is not found.

final notes = <String>['do', 're', 'mi', 're'];
final index = notes.indexOf('fa'); // -1

int indexOf(E element, [int start = 0]);

indexWhere()#

The first index in the list that satisfies the provided test.

Searches the list from index start to the end of the list. The first time an object o is encountered so that test(o) is true, the index of o is returned.

final notes = <String>['do', 're', 'mi', 're'];
final first = notes.indexWhere((note) => note.startsWith('r')); // 1
final second = notes.indexWhere((note) => note.startsWith('r'), 2); // 3

Returns -1 if element is not found.

final notes = <String>['do', 're', 'mi', 're'];
final index = notes.indexWhere((note) => note.startsWith('k')); // -1

int indexWhere(bool test(E element), [int start = 0]);

insert()#

Inserts element at position index in this list.

This increases the length of the list by one and shifts all objects at or after the index towards the end of the list.

The list must be growable. The index value must be non-negative and no greater than length.

final numbers = <int>[1, 2, 3, 4];
const index = 2;
numbers.insert(index, 10);
print(numbers); // [1, 2, 10, 3, 4]

void insert(int index, E element);

insertAll()#

Inserts all objects of iterable at position index in this list.

This increases the length of the list by the length of iterable and shifts all later objects towards the end of the list.

The list must be growable. The index value must be non-negative and no greater than length.

final numbers = <int>[1, 2, 3, 4];
final insertItems = [10, 11];
numbers.insertAll(2, insertItems);
print(numbers); // [1, 2, 10, 11, 3, 4]

void insertAll(int index, Iterable<E> iterable);

join() inherited#

Converts each element to a String and concatenates the strings.

Iterates through elements of this iterable, converts each one to a String by calling Object.toString, and then concatenates the strings, with the separator string interleaved between the elements.

Example:

final planetsByMass = <double, String>{0.06: 'Mercury', 0.81: 'Venus',
  0.11: 'Mars'};
final joinedNames = planetsByMass.values.join('-'); // Mercury-Venus-Mars

Inherited from Iterable.

String join([String separator = ""]) {
  Iterator<E> iterator = this.iterator;
  if (!iterator.moveNext()) return "";
  var first = iterator.current.toString();
  if (!iterator.moveNext()) return first;
  var buffer = StringBuffer(first);
  &#47;&#47; TODO(51681): Drop null check when de-supporting pre-2.12 code.
  if (separator == null || separator.isEmpty) {
    do {
      buffer.write(iterator.current.toString());
    } while (iterator.moveNext());
  } else {
    do {
      buffer
        ..write(separator)
        ..write(iterator.current.toString());
    } while (iterator.moveNext());
  }
  return buffer.toString();
}

lastIndexOf()#

The last index of element in this list.

Searches the list backwards from index start to 0.

The first time an object o is encountered so that o == element, the index of o is returned.

final notes = <String>['do', 're', 'mi', 're'];
const startIndex = 2;
final index = notes.lastIndexOf('re', startIndex); // 1

If start is not provided, this method searches from the end of the list.

final notes = <String>['do', 're', 'mi', 're'];
final index = notes.lastIndexOf('re'); // 3

Returns -1 if element is not found.

final notes = <String>['do', 're', 'mi', 're'];
final index = notes.lastIndexOf('fa'); // -1

int lastIndexOf(E element, [int? start]);

lastIndexWhere()#

The last index in the list that satisfies the provided test.

Searches the list from index start to 0. The first time an object o is encountered so that test(o) is true, the index of o is returned. If start is omitted, it defaults to the length of the list.

final notes = <String>['do', 're', 'mi', 're'];
final first = notes.lastIndexWhere((note) => note.startsWith('r')); // 3
final second = notes.lastIndexWhere((note) => note.startsWith('r'),
    2); // 1

Returns -1 if element is not found.

final notes = <String>['do', 're', 'mi', 're'];
final index = notes.lastIndexWhere((note) => note.startsWith('k'));
print(index); // -1

int lastIndexWhere(bool test(E element), [int? start]);

lastWhere() inherited#

The last element that satisfies the given predicate test.

An iterable that can access its elements directly may check its elements in any order (for example a list starts by checking the last element and then moves towards the start of the list). The default implementation iterates elements in iteration order, checks test(element) for each, and finally returns that last one that matched.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
var result = numbers.lastWhere((element) => element < 5); // 3
result = numbers.lastWhere((element) => element > 5); // 7
result = numbers.lastWhere((element) => element > 10,
    orElse: () => -1); // -1

If no element satisfies test, the result of invoking the orElse function is returned. If orElse is omitted, it defaults to throwing a StateError.

Inherited from Iterable.

E lastWhere(bool test(E element), {E orElse()?}) {
  var iterator = this.iterator;
  // Potential result during first loop.
  E result;
  do {
    if (!iterator.moveNext()) {
      if (orElse != null) return orElse();
      throw IterableElementError.noElement();
    }
    result = iterator.current;
  } while (!test(result));
  // Now `result` is actual result, unless a later one is found.
  while (iterator.moveNext()) {
    var current = iterator.current;
    if (test(current)) result = current;
  }
  return result;
}

map() inherited#

The current elements of this iterable modified by toElement.

Returns a new lazy Iterable with elements that are created by calling toElement on each element of this Iterable in iteration order.

The returned iterable is lazy, so it won't iterate the elements of this iterable until it is itself iterated, and then it will apply toElement to create one element at a time. The converted elements are not cached. Iterating multiple times over the returned Iterable will invoke the supplied toElement function once per element for on each iteration.

Methods on the returned iterable are allowed to omit calling toElement on any element where the result isn't needed. For example, elementAt may call toElement only once.

Equivalent to:

Iterable<T> map<T>(T toElement(E e)) sync* {
  for (var value in this) {
    yield toElement(value);
  }
}

Example:

var products = jsonDecode('''
[
  {"name": "Screwdriver", "price": 42.00},
  {"name": "Wingnut", "price": 0.50}
]
''');
var values = products.map((product) => product['price'] as double);
var totalPrice = values.fold(0.0, (a, b) => a + b); // 42.5.

Inherited from Iterable.

Iterable<T> map<T>(T toElement(E e)) => MappedIterable<E, T>(this, toElement);

noSuchMethod() inherited#

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

reduce() inherited#

Reduces a collection to a single value by iteratively combining elements of the collection using the provided function.

The iterable must have at least one element. If it has only one element, that element is returned.

Otherwise this method starts with the first element from the iterator, and then combines it with the remaining elements in iteration order, as if by:

E value = iterable.first;
iterable.skip(1).forEach((element) {
  value = combine(value, element);
});
return value;

Example of calculating the sum of an iterable:

final numbers = <double>[10, 2, 5, 0.5];
final result = numbers.reduce((value, element) => value + element);
print(result); // 17.5

Consider using fold if the iterable can be empty.

Inherited from Iterable.

E reduce(E combine(E value, E element)) {
  Iterator<E> iterator = this.iterator;
  if (!iterator.moveNext()) {
    throw IterableElementError.noElement();
  }
  E value = iterator.current;
  while (iterator.moveNext()) {
    value = combine(value, iterator.current);
  }
  return value;
}

remove()#

Removes the first occurrence of value from this list.

Returns true if value was in the list, false otherwise. The list must be growable.

final parts = <String>['head', 'shoulders', 'knees', 'toes'];
final retVal = parts.remove('head'); // true
print(parts); // [shoulders, knees, toes]

The method has no effect if value was not in the list.

final parts = <String>['shoulders', 'knees', 'toes'];
// Note: 'head' has already been removed.
final retVal = parts.remove('head'); // false
print(parts); // [shoulders, knees, toes]

bool remove(Object? value);

removeAt()#

Removes the object at position index from this list.

This method reduces the length of this by one and moves all later objects down by one position.

Returns the removed value.

The index must be in the range 0 ≤ index < length. The list must be growable.

final parts = <String>['head', 'shoulder', 'knees', 'toes'];
final retVal = parts.removeAt(2); // knees
print(parts); // [head, shoulder, toes]

E removeAt(int index);

removeLast()#

Removes and returns the last object in this list.

The list must be growable and non-empty.

final parts = <String>['head', 'shoulder', 'knees', 'toes'];
final retVal = parts.removeLast(); // toes
print(parts); // [head, shoulder, knees]

E removeLast();

removeRange()#

Removes a range of elements from the list.

Removes the elements with positions greater than or equal to start and less than end, from the list. This reduces the list's length by end - start.

The provided range, given by start and end, must be valid. A range from start to end is valid if 0 ≤ start ≤ end ≤ length. An empty range (with end == start) is valid.

The list must be growable.

final numbers = <int>[1, 2, 3, 4, 5];
numbers.removeRange(1, 4);
print(numbers); // [1, 5]

void removeRange(int start, int end);

removeWhere()#

Removes all objects from this list that satisfy test.

An object o satisfies test if test(o) is true.

final numbers = <String>['one', 'two', 'three', 'four'];
numbers.removeWhere((item) => item.length == 3);
print(numbers); // [three, four]

The list must be growable.

void removeWhere(bool test(E element));

replaceRange()#

Replaces a range of elements with the elements of replacements.

Removes the objects in the range from start to end, then inserts the elements of replacements at start.

final numbers = <int>[1, 2, 3, 4, 5];
final replacements = [6, 7];
numbers.replaceRange(1, 4, replacements);
print(numbers); // [1, 6, 7, 5]

The provided range, given by start and end, must be valid. A range from start to end is valid if 0 ≤ start ≤ end ≤ length. An empty range (with end == start) is valid.

The operation list.replaceRange(start, end, replacements) is roughly equivalent to:

final numbers = <int>[1, 2, 3, 4, 5];
numbers.removeRange(1, 4);
final replacements = [6, 7];
numbers.insertAll(1, replacements);
print(numbers); // [1, 6, 7, 5]

but may be more efficient.

The list must be growable. This method does not work on fixed-length lists, even when replacements has the same number of elements as the replaced range. In that case use setRange instead.

void replaceRange(int start, int end, Iterable<E> replacements);

retainWhere()#

Removes all objects from this list that fail to satisfy test.

An object o satisfies test if test(o) is true.

final numbers = <String>['one', 'two', 'three', 'four'];
numbers.retainWhere((item) => item.length == 3);
print(numbers); // [one, two]

The list must be growable.

void retainWhere(bool test(E element));

setAll()#

Overwrites elements with the objects of iterable.

The elements of iterable are written into this list, starting at position index. This operation does not increase the length of the list.

The index must be non-negative and no greater than length.

The iterable must not have more elements than what can fit from index to length.

If iterable is based on this list, its values may change during the setAll operation.

final list = <String>['a', 'b', 'c', 'd'];
list.setAll(1, ['bee', 'sea']);
print(list); // [a, bee, sea, d]

void setAll(int index, Iterable<E> iterable);

setRange()#

Writes some elements of iterable into a range of this list.

Copies the objects of iterable, skipping skipCount objects first, into the range from start, inclusive, to end, exclusive, of this list.

final list1 = <int>[1, 2, 3, 4];
final list2 = <int>[5, 6, 7, 8, 9];
// Copies the 4th and 5th items in list2 as the 2nd and 3rd items
// of list1.
const skipCount = 3;
list1.setRange(1, 3, list2, skipCount);
print(list1); // [1, 8, 9, 4]

The provided range, given by start and end, must be valid. A range from start to end is valid if 0 ≤ start ≤ end ≤ length. An empty range (with end == start) is valid.

The iterable must have enough objects to fill the range from start to end after skipping skipCount objects.

If iterable is this list, the operation correctly copies the elements originally in the range from skipCount to skipCount + (end - start) to the range start to end, even if the two ranges overlap.

If iterable depends on this list in some other way, no guarantees are made.

void setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]);

shuffle()#

Shuffles the elements of this list randomly.

final numbers = <int>[1, 2, 3, 4, 5];
numbers.shuffle();
print(numbers); // [1, 3, 4, 5, 2] OR some other random result.

void shuffle([Random? random]);

singleWhere() inherited#

The single element that satisfies test.

Checks elements to see if test(element) returns true. If exactly one element satisfies test, that element is returned. If more than one matching element is found, throws StateError. If no matching element is found, returns the result of orElse. If orElse is omitted, it defaults to throwing a StateError.

Example:

final numbers = <int>[2, 2, 10];
var result = numbers.singleWhere((element) => element > 5); // 10

When no matching element is found, the result of calling orElse is returned instead.

result = numbers.singleWhere((element) => element == 1,
    orElse: () => -1); // -1

There must not be more than one matching element.

result = numbers.singleWhere((element) => element == 2); // Throws Error.

Inherited from Iterable.

E singleWhere(bool test(E element), {E orElse()?}) {
  var iterator = this.iterator;
  E result;
  do {
    if (!iterator.moveNext()) {
      if (orElse != null) return orElse();
      throw IterableElementError.noElement();
    }
    result = iterator.current;
  } while (!test(result));
  while (iterator.moveNext()) {
    if (test(iterator.current)) throw IterableElementError.tooMany();
  }
  return result;
}

skip() inherited#

Creates an Iterable that provides all but the first count elements.

When the returned iterable is iterated, it starts iterating over this, first skipping past the initial count elements. If this has fewer than count elements, then the resulting Iterable is empty. After that, the remaining elements are iterated in the same order as in this iterable.

Some iterables may be able to find later elements without first iterating through earlier elements, for example when iterating a List. Such iterables are allowed to ignore the initial skipped elements.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
final result = numbers.skip(4); // (6, 7)
final skipAll = numbers.skip(100); // () - no elements.

The count must not be negative.

Inherited from Iterable.

Iterable<E> skip(int count) => SkipIterable<E>(this, count);

skipWhile() inherited#

Creates an Iterable that skips leading elements while test is satisfied.

The filtering happens lazily. Every new Iterator of the returned iterable iterates over all elements of this.

The returned iterable provides elements by iterating this iterable, but skipping over all initial elements where test(element) returns true. If all elements satisfy test the resulting iterable is empty, otherwise it iterates the remaining elements in their original order, starting with the first element for which test(element) returns false.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
var result = numbers.skipWhile((x) => x < 5); // (5, 6, 7)
result = numbers.skipWhile((x) => x != 3); // (3, 5, 6, 7)
result = numbers.skipWhile((x) => x != 4); // ()
result = numbers.skipWhile((x) => x.isOdd); // (2, 3, 5, 6, 7)

Inherited from Iterable.

Iterable<E> skipWhile(bool test(E value)) => SkipWhileIterable<E>(this, test);

sort()#

Sorts this list according to the order specified by the compare function.

The compare function must act as a Comparator.

final numbers = <String>['two', 'three', 'four'];
// Sort from shortest to longest.
numbers.sort((a, b) => a.length.compareTo(b.length));
print(numbers); // [two, four, three]

The default List implementations use Comparable.compare if compare is omitted.

final numbers = <int>[13, 2, -11, 0];
numbers.sort();
print(numbers); // [-11, 0, 2, 13]

In that case, the elements of the list must be Comparable to each other.

A Comparator may compare objects as equal (return zero), even if they are distinct objects. The sort function is not guaranteed to be stable, so distinct objects that compare as equal may occur in any order in the result:

final numbers = <String>['one', 'two', 'three', 'four'];
numbers.sort((a, b) => a.length.compareTo(b.length));
print(numbers); // [one, two, four, three] OR [two, one, four, three]

void sort([int compare(E a, E b)?]);

sublist()#

Returns a new list containing the elements between start and end.

The new list is a List<E> containing the elements of this list at positions greater than or equal to start and less than end in the same order as they occur in this list.

final colors = <String>['red', 'green', 'blue', 'orange', 'pink'];
print(colors.sublist(1, 3)); // [green, blue]

If end is omitted, it defaults to the length of this list.

final colors = <String>['red', 'green', 'blue', 'orange', 'pink'];
print(colors.sublist(3)); // [orange, pink]

The start and end positions must satisfy the relations 0 ≤ start ≤ end ≤ length. If end is equal to start, then the returned list is empty.

List<E> sublist(int start, [int? end]);

take() inherited#

Creates a lazy iterable of the count first elements of this iterable.

The returned Iterable may contain fewer than count elements, if this contains fewer than count elements.

The elements can be computed by stepping through iterator until count elements have been seen.

The count must not be negative.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
final result = numbers.take(4); // (1, 2, 3, 5)
final takeAll = numbers.take(100); // (1, 2, 3, 5, 6, 7)

Inherited from Iterable.

Iterable<E> take(int count) => TakeIterable<E>(this, count);

takeWhile() inherited#

Creates a lazy iterable of the leading elements satisfying test.

The filtering happens lazily. Every new iterator of the returned iterable starts iterating over the elements of this.

The elements can be computed by stepping through iterator until an element is found where test(element) is false. At that point, the returned iterable stops (its moveNext() returns false).

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
var result = numbers.takeWhile((x) => x < 5); // (1, 2, 3)
result = numbers.takeWhile((x) => x != 3); // (1, 2)
result = numbers.takeWhile((x) => x != 4); // (1, 2, 3, 5, 6, 7)
result = numbers.takeWhile((x) => x.isOdd); // (1)

Inherited from Iterable.

Iterable<E> takeWhile(bool test(E value)) => TakeWhileIterable<E>(this, test);

toList() inherited#

Creates a List containing the elements of this Iterable.

The elements are in iteration order. The list is fixed-length if growable is false.

Example:

final planets = <int, String>{1: 'Mercury', 2: 'Venus', 3: 'Mars'};
final keysList = planets.keys.toList(growable: false); // [1, 2, 3]
final valuesList =
    planets.values.toList(growable: false); // [Mercury, Venus, Mars]

Inherited from Iterable.

List<E> toList({bool growable = true}) =>
    List<E>.of(this, growable: growable);

toSet() inherited#

Creates a Set containing the same elements as this iterable.

The set may contain fewer elements than the iterable, if the iterable contains an element more than once, or it contains one or more elements that are equal. The order of the elements in the set is not guaranteed to be the same as for the iterable.

Example:

final planets = <int, String>{1: 'Mercury', 2: 'Venus', 3: 'Mars'};
final valueSet = planets.values.toSet(); // {Mercury, Venus, Mars}

Inherited from Iterable.

Set<E> toSet() => Set<E>.of(this);

toString() inherited#

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

external String toString();

where() inherited#

Creates a new lazy Iterable with all elements that satisfy the predicate test.

The matching elements have the same order in the returned iterable as they have in iterator.

This method returns a view of the mapped elements. As long as the returned Iterable is not iterated over, the supplied function test will not be invoked. Iterating will not cache results, and thus iterating multiple times over the returned Iterable may invoke the supplied function test multiple times on the same element.

Example:

final numbers = <int>[1, 2, 3, 5, 6, 7];
var result = numbers.where((x) => x < 5); // (1, 2, 3)
result = numbers.where((x) => x > 5); // (6, 7)
result = numbers.where((x) => x.isEven); // (2, 6)

Inherited from Iterable.

Iterable<E> where(bool test(E element)) => WhereIterable<E>(this, test);

whereType() inherited#

Creates a new lazy Iterable with all elements that have type T.

The matching elements have the same order in the returned iterable as they have in iterator.

This method returns a view of the mapped elements. Iterating will not cache results, and thus iterating multiple times over the returned Iterable may yield different results, if the underlying elements change between iterations.

Inherited from Iterable.

Iterable<T> whereType<T>() => WhereTypeIterable<T>(this);

Operators#

operator +()#

Returns the concatenation of this list and other.

Returns a new list containing the elements of this list followed by the elements of other.

The default behavior is to return a normal growable list. Some list types may choose to return a list of the same type as themselves (see Uint8List.+);

List<E> operator +(List<E> other);

operator ==() override#

Whether this list is equal to other.

Lists are, by default, only equal to themselves. Even if other is also a list, the equality comparison does not compare the elements of the two lists.

bool operator ==(Object other);

operator []()#

The object at the given index in the list.

The index must be a valid index of this list, which means that index must be non-negative and less than length.

E operator [](int index);

operator []=()#

Sets the value at the given index in the list to value.

The index must be a valid index of this list, which means that index must be non-negative and less than length.

void operator []=(int index, E value);

Static Methods#

castFrom() override#

Adapts source to be a List<T>.

Any time the list would produce an element that is not a T, the element access will throw.

Any time a T value is attempted stored into the adapted list, the store will throw unless the value is also an instance of S.

If all accessed elements of source are actually instances of T, and if all elements stored into the returned list are actually instance of S, then the returned list can be used as a List<T>.

Methods which accept Object? as argument, like contains and remove, will pass the argument directly to the this list's method without any checks.

static List<T> castFrom<S, T>(List<S> source) => CastList<S, T>(source);

copyRange()#

Copy a range of one list into another list.

This is a utility function that can be used to implement methods like setRange.

The range from start to end must be a valid range of source, and there must be room for end - start elements from position at. If start is omitted, it defaults to zero. If end is omitted, it defaults to source.length.

If source and target are the same list, overlapping source and target ranges are respected so that the target range ends up containing the initial content of the source range. Otherwise the order of element copying is not guaranteed.

static void copyRange<T>(
  List<T> target,
  int at,
  List<T> source, [
  int? start,
  int? end,
]) {
  start ??= 0;
  end = RangeError.checkValidRange(start, end, source.length);

  int length = end - start;
  if (target.length < at + length) {
    throw ArgumentError.value(
      target,
      "target",
      "Not big enough to hold $length elements at position $at",
    );
  }
  if (!identical(source, target) || start >= at) {
    for (int i = 0; i < length; i++) {
      target[at + i] = source[start + i];
    }
  } else {
    for (int i = length; --i >= 0;) {
      target[at + i] = source[start + i];
    }
  }
}

writeIterable()#

Write the elements of an iterable into a list.

This is a utility function that can be used to implement methods like setAll.

The elements of source are written into target from position at. The source must not contain more elements after writing the last position of target.

If the source is a list, the copyRange function is likely to be more efficient.

static void writeIterable<T>(List<T> target, int at, Iterable<T> source) {
  RangeError.checkValueInInterval(at, 0, target.length, "at");
  int index = at;
  int targetLength = target.length;
  for (var element in source) {
    if (index == targetLength) {
      throw IndexError.withLength(index, targetLength, indexable: target);
    }
    target[index] = element;
    index++;
  }
}