IndexError

class IndexError extends ArgumentError implements RangeError

A specialized RangeError used when an index is not in the range 0..indexable.length-1.

Also contains the indexable object, its length at the time of the error, and the invalid index itself.

Inheritance

Object → Error → ArgumentError → IndexError

Implemented types

• RangeError

Constructors

deprecated IndexError()

IndexError(
  int invalidValue,
  dynamic indexable, [
  String? name,
  String? message,
  int? length,
])

DEPRECATED

Use IndexError.withLength instead.

Creates a new IndexError stating that invalidValue is not a valid index into indexable.

The length is the length of indexable at the time of the error. If length is omitted, it defaults to indexable.length.

The message is used as part of the string representation of the error.

Implementation

@Deprecated("Use IndexError.withLength instead.")
IndexError(
  int invalidValue,
  dynamic indexable, [
  String? name,
  String? message,
  int? length,
]) : this.indexable = indexable,
     // ignore: avoid_dynamic_calls
     this.length = length ?? indexable.length,
     super.value(invalidValue, name, message ?? "Index out of range");

IndexError.withLength()

IndexError.withLength(
  int invalidValue,
  int length, {
  Object? indexable,
  String? name,
  String? message,
})

Creates a new IndexError stating that invalidValue is not a valid index into indexable.

The length is the length of indexable at the time of the error.

The message is used as part of the string representation of the error.

Implementation

@Since("2.19")
IndexError.withLength(
  int invalidValue,
  this.length, {
  this.indexable,
  String? name,
  String? message,
}) : super.value(invalidValue, name, message ?? "Index out of range");

Properties

end no setter override

int get end

The maximum value that value is allowed to assume.

Implementation

int get end => length - 1;

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;

indexable final

final Object? indexable

The indexable object that invalidValue was not a valid index into.

Can be, for example, a List or String, which both have index based operations.

Implementation

final Object? indexable;

invalidValue no setter override

int get invalidValue

The invalid value.

Implementation

int get invalidValue => super.invalidValue;

length final

final int length

The length of indexable at the time of the error.

Implementation

final int length;

message final inherited

final dynamic message

Message describing the problem.

Inherited from ArgumentError.

Implementation

final dynamic message;

name final inherited

final String? name

Name of the invalid argument, if available.

Inherited from ArgumentError.

Implementation

final String? name;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

stackTrace no setter inherited

StackTrace? get stackTrace

The stack trace at the point where this error was first thrown.

Classes which extend Error will automatically have a stack trace filled in the first time they are thrown by a throw expression.

Inherited from Error.

Implementation

external StackTrace? get stackTrace;

start no setter override

int get start

The minimum value that value is allowed to assume.

Implementation

int get start => 0;

Methods

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 ArgumentError.

Implementation

String toString() {
  String? name = this.name;
  String nameString = (name == null) ? "" : " ($name)";
  Object? message = this.message;
  var messageString = (message == null) ? "" : ": ${message}";
  String prefix = "$_errorName$nameString$messageString";
  if (!_hasValue) return prefix;
  // If we know the invalid value, we can try to describe the problem.
  String explanation = _errorExplanation;
  String errorValue = Error.safeToString(invalidValue);
  return "$prefix$explanation: $errorValue";
}

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);

Static Methods

check()

int check(
  int index,
  int length, {
  Object? indexable,
  String? name,
  String? message,
})

Check that index is a valid index into an indexable object.

Throws if index is not a valid index.

An indexable object is one that has a length and an index-operator [] that accepts an index if 0 <= index < length.

The length is the length of the indexable object.

The indexable, if provided, is the indexable object.

The name is the parameter name of the index value. Defaults to "index", and can be set to null to omit a name from the error string, if the invalid index was not a parameter.

The message, if provided, is included in the error string.

Returns index if it is a valid index.

Implementation

@Since("2.19")
static int check(
  int index,
  int length, {
  Object? indexable,
  String? name,
  String? message,
}) {
  // Comparing with `0` as receiver produces better dart2js type inference.
  if (0 > index || index >= length) {
    name ??= "index";
    throw IndexError.withLength(
      index,
      length,
      indexable: indexable,
      name: name,
      message: message,
    );
  }
  return index;
}