RuneIterator final

final class RuneIterator implements Iterator<int>

Iterator for reading runes (integer Unicode code points) of a Dart string.

Implemented types

• Iterator<E>

Constructors

RuneIterator()

RuneIterator(String string)

Create an iterator positioned at the beginning of the string.

Implementation

RuneIterator(String string)
  : this.string = string,
    _position = 0,
    _nextPosition = 0;

RuneIterator.at()

RuneIterator.at(String string, int index)

Create an iterator positioned before the indexth code unit of the string.

When created, there is no current value. A moveNext will use the rune starting at index the current value, and a movePrevious will use the rune ending just before index as the current value.

The index position must not be in the middle of a surrogate pair.

Implementation

RuneIterator.at(String string, int index)
  : string = string,
    _position = index,
    _nextPosition = index {
  RangeError.checkValueInInterval(index, 0, string.length);
  _checkSplitSurrogate(index);
}

Properties

current no setter override

int get current

The rune (integer Unicode code point) starting at the current position in the string.

The value is -1 if there is no current code point.

Implementation

int get current => _currentCodePoint;

currentAsString no setter

String get currentAsString

A string containing the current rune.

For runes outside the basic multilingual plane, this will be a String of length 2, containing two code units.

Returns an empty string if there is no current value.

Implementation

String get currentAsString {
  if (_position == _nextPosition) return "";
  if (_position + 1 == _nextPosition) return string[_position];
  return string.substring(_position, _nextPosition);
}

currentSize no setter

int get currentSize

The number of code units comprising the current rune.

Returns zero if there is no current rune (current is -1).

Implementation

int get currentSize => _nextPosition - _position;

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;

rawIndex read / write

int get rawIndex

getter:

The starting position of the current rune in the string.

Returns -1 if there is no current rune (current is -1).

setter:

Resets the iterator to the rune at the specified index of the string.

Setting a negative rawIndex, or one greater than or equal to string.length, is an error. So is setting it in the middle of a surrogate pair.

Setting the position to the end of the string means that there is no current rune.

Implementation

int get rawIndex => (_position != _nextPosition) ? _position : -1;

void set rawIndex(int rawIndex) {
  IndexError.check(
    rawIndex,
    string.length,
    indexable: string,
    name: "rawIndex",
  );
  reset(rawIndex);
  moveNext();
}

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

string final

final String string

String being iterated.

Implementation

final String string;

Methods

moveNext() override

bool moveNext()

Move to the next code point.

Returns true and updates current if there is a next code point. Returns false otherwise, and then there is no current code point.

Implementation

bool moveNext() {
  _position = _nextPosition;
  if (_position == string.length) {
    _currentCodePoint = -1;
    return false;
  }
  int codeUnit = string.codeUnitAt(_position);
  int nextPosition = _position + 1;
  if (_isLeadSurrogate(codeUnit) && nextPosition < string.length) {
    int nextCodeUnit = string.codeUnitAt(nextPosition);
    if (_isTrailSurrogate(nextCodeUnit)) {
      _nextPosition = nextPosition + 1;
      _currentCodePoint = _combineSurrogatePair(codeUnit, nextCodeUnit);
      return true;
    }
  }
  _nextPosition = nextPosition;
  _currentCodePoint = codeUnit;
  return true;
}

movePrevious()

bool movePrevious()

Move back to the previous code point.

Returns true and updates current if there is a previous code point. Returns false otherwise, and then there is no current code point.

Implementation

bool movePrevious() {
  _nextPosition = _position;
  if (_position == 0) {
    _currentCodePoint = -1;
    return false;
  }
  int position = _position - 1;
  int codeUnit = string.codeUnitAt(position);
  if (_isTrailSurrogate(codeUnit) && position > 0) {
    int prevCodeUnit = string.codeUnitAt(position - 1);
    if (_isLeadSurrogate(prevCodeUnit)) {
      _position = position - 1;
      _currentCodePoint = _combineSurrogatePair(prevCodeUnit, codeUnit);
      return true;
    }
  }
  _position = position;
  _currentCodePoint = codeUnit;
  return true;
}

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);

reset()

void reset([int rawIndex = 0])

Resets the iterator to the given index into the string.

After this the current value is unset. You must call moveNext make the rune at the position current, or movePrevious for the last rune before the position.

The rawIndex must be non-negative and no greater than string.length. It must also not be the index of the trailing surrogate of a surrogate pair.

Implementation

void reset([int rawIndex = 0]) {
  RangeError.checkValueInInterval(rawIndex, 0, string.length, "rawIndex");
  _checkSplitSurrogate(rawIndex);
  _position = _nextPosition = rawIndex;
  _currentCodePoint = -1;
}

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);