StreamIterator<T> abstract interface

abstract interface class StreamIterator<T>

An Iterator-like interface for the values of a Stream.

This wraps a Stream and a subscription on the stream. It listens on the stream, and completes the future returned by moveNext when the next value becomes available.

The stream may be paused between calls to moveNext.

The current value must only be used after a future returned by moveNext has completed with true, and only until moveNext is called again.

Constructors

StreamIterator() factory

factory StreamIterator(Stream<T> stream)

Create a StreamIterator on stream.

Implementation

factory StreamIterator(Stream<T> stream) =>
    &#47;&#47; TODO(lrn): use redirecting factory constructor when type
    &#47;&#47; arguments are supported.
    _StreamIterator<T>(stream);

Properties

current no setter

T get current

The current value of the stream.

When a moveNext call completes with true, the current field holds the most recent event of the stream, and it stays like that until the next call to moveNext. This value must only be read after a call to moveNext has completed with true, and only until the moveNext is called again.

If the StreamIterator has not yet been moved to the first element (moveNext has not been called and completed yet), or if the StreamIterator has been moved past the last element (moveNext has returned false), then current is unspecified. A StreamIterator may either throw or return an iterator-specific default value in that case.

Implementation

T get current;

hashCode no setter inherited

int get hashCode

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.

Implementation

external int get hashCode;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

cancel()

Future<dynamic> cancel()

Cancels the stream iterator (and the underlying stream subscription) early.

The stream iterator is automatically canceled if the moveNext future completes with either false or an error.

If you need to stop listening for values before the stream iterator is automatically closed, you must call cancel to ensure that the stream is properly closed.

If moveNext has been called when the iterator is canceled, its returned future will complete with false as value, as will all further calls to moveNext.

Returns a future which completes when the cancellation is complete. This can be an already completed future if the cancellation happens synchronously.

Implementation

Future cancel();

moveNext()

Future<bool> moveNext()

Wait for the next stream value to be available.

Returns a future which will complete with either true or false. Completing with true means that another event has been received and can be read as current. Completing with false means that the stream iteration is done and no further events will ever be available. The future may complete with an error, if the stream produces an error, which also ends iteration.

The function must not be called again until the future returned by a previous call is completed.

Implementation

Future<bool> moveNext();

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

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.

Implementation

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

toString() inherited

String toString()

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.

Implementation

external String toString();

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

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

Inherited from Object.

Implementation

external bool operator ==(Object other);