dart:core library

Built-in types, collections, and other core functionality for every Dart program.

This library is automatically imported.

Some classes in this library, such as String and num, support Dart's built-in data types. Other classes, such as List and Map, provide data structures for managing collections of objects. And still other classes represent commonly used types of data such as URIs, dates and times, and errors.

Numbers and booleans

int and double provide support for Dart's built-in numerical data types: integers and double-precision floating point numbers, respectively. An object of type bool is either true or false. Variables of these types can be constructed from literals:

int meaningOfLife = 42;
double valueOfPi  = 3.141592;
bool visible      = true;

Strings and regular expressions

A String is immutable and represents a sequence of characters.

String shakespeareQuote = "All the world's a stage, ...";

StringBuffer provides a way to construct strings efficiently.

var moreShakespeare = StringBuffer();
moreShakespeare.write('And all the men and women ');
moreShakespeare.write('merely players; ...');

The String and StringBuffer classes implement string splitting, concatenation, and other string manipulation features.

bool isPalindrome(String text) => text == text.split('').reversed.join();

RegExp implements Dart regular expressions, which provide a grammar for matching patterns within text. For example, here's a regular expression that matches a substring containing one or more digits:

var numbers = RegExp(r'\d+');

Dart regular expressions have the same syntax and semantics as JavaScript regular expressions. See ecma-international.org/ecma-262/5.1/#sec-15.10 for the specification of JavaScript regular expressions.

Collections

The dart:core library provides basic collections, such as List, Map, and Set.

A List is an ordered collection of objects, with a length. Lists are sometimes called arrays. Use a List when you need to access objects by index.

var superheroes = ['Batman', 'Superman', 'Harry Potter'];

A Set is an unordered collection of unique objects. You cannot get an item efficiently by index (position). Adding an element which is already in the set, has no effect.

var villains = {'Joker'};
print(villains.length); // 1
villains.addAll(['Joker', 'Lex Luthor', 'Voldemort']);
print(villains.length); // 3

A Map is an unordered collection of key-value pairs, where each key can only occur once. Maps are sometimes called associative arrays because maps associate a key to some value for easy retrieval. Use a Map when you need to access objects by a unique identifier.

var sidekicks = {'Batman': 'Robin',
                 'Superman': 'Lois Lane',
                 'Harry Potter': 'Ron and Hermione'};

In addition to these classes, dart:core contains Iterable, an interface that defines functionality common in collections of objects. Examples include the ability to run a function on each element in the collection, to apply a test to each element, to retrieve an object, and to determine the number of elements.

Iterable is implemented by List and Set, and used by Map for its keys and values.

For other kinds of collections, check out the dart:collection library.

Date and time

Use DateTime to represent a point in time and Duration to represent a span of time.

You can create DateTime objects with constructors or by parsing a correctly formatted string.

var now = DateTime.now();
var berlinWallFell = DateTime(1989, 11, 9);
var moonLanding = DateTime.parse("1969-07-20");

Create a Duration object by specifying the individual time units.

var timeRemaining = const Duration(hours: 56, minutes: 14);

In addition to DateTime and Duration, dart:core contains the Stopwatch class for measuring elapsed time.

Uri

A Uri object represents a uniform resource identifier, which identifies a resource, for example on the web.

var dartlang = Uri.parse('http://dartlang.org/');

Errors

The Error class represents the occurrence of an error during runtime. Subclasses of this class represent specific kinds of errors.

Other documentation

For more information about how to use the built-in types, refer to Built-in Types in A tour of the Dart language.

Also, see dart:core - numbers, collections, strings, and more for more coverage of types in this library.

The Dart Language Specification provides technical details.

Classes

BidirectionalIterator<E>

An Iterator that allows moving backwards as well as forwards.

BigInt

An arbitrarily large integer.

bool

The reserved words true and false denote objects that are the only two instances of this class. [...]

Comparable<T>

Interface used by types that have an intrinsic ordering. [...]

DateTime

An instant in time, such as July 20, 1969, 8:18pm GMT. [...]

Deprecated

The annotation @Deprecated('migration') marks a feature as deprecated. [...]

double

A double-precision floating point number. [...]

Duration

A span of time, such as 27 days, 4 hours, 12 minutes, and 3 seconds. [...]

Expando<T extends Object>

An Expando allows adding new properties to objects. [...]

Function

The base class for all function types. [...]

Future<T>

An object representing a delayed computation. [...]

int

An integer number. [...]

Invocation

Representation of the invocation of a member on an object. [...]

Iterable<E>

A collection of values, or "elements", that can be accessed sequentially. [...]

Iterator<E>

An interface for getting items, one at a time, from an object. [...]

List<E>

An indexable collection of objects with a length. [...]

Map<K, V>

A collection of key/value pairs, from which you retrieve a value using its associated key. [...]

MapEntry<K, V>

A key/value pair representing an entry in a Map.

Match

A result from searching within a string. [...]

Null

The reserved word null denotes an object that is the sole instance of this class. [...]

num

An integer or floating-point number. [...]

Object

The base class for all Dart objects exception null. [...]

Pattern

An interface for basic searches within strings.

pragma

A hint to tools. [...]

Provisional

An annotation class that was used during development of Dart 2. [...]

RegExp

A regular expression pattern. [...]

RegExpMatch

A regular expression match. [...]

RuneIterator

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

Runes

The runes (integer Unicode code points) of a String.

Set<E>

A collection of objects in which each object can occur only once. [...]

Sink<T>

A generic destination for data. [...]

StackTrace

An interface implemented by all stack trace objects. [...]

Stopwatch

A simple stopwatch interface to measure elapsed time.

Stream<T>

A source of asynchronous data events. [...]

String

A sequence of UTF-16 code units. [...]

StringBuffer

A class for concatenating strings efficiently. [...]

StringSink

Symbol

Opaque name used by mirrors, invocations and Function.apply.

Type

Runtime representation of a type. [...]

Uri

A parsed URI, such as a URL. [...]

UriData

A way to access the structure of a data: URI. [...]

Extensions

FutureExtensions

Convenience methods on futures. [...]

Constants

deprecated → const Deprecated

Marks a feature as Deprecated until the next release.

const Deprecated("next release")

override → const Object

Annotation on an instance members which override an interface member. [...]

const _Override()

provisional → const Null

An annotation that was used during development of Dart 2. [...]

null

proxy → const Null

This annotation was used in Dart prior to version 2. [...]

null

Functions

identical(Object? a, Object? b) → bool

Check whether two references are to the same object.

identityHashCode(Object? object) → int

The identity hash code of object. [...]

print(Object? object) → void

Prints a string representation of the object to the console.

Typedefs

Comparator<T>(T a, T b) → int

The signature of a generic comparison function. [...]

Exceptions / Errors

AbstractClassInstantiationError

Error thrown when trying to instantiate an abstract class. [...]

ArgumentError

Error thrown when a function is passed an unacceptable argument.

AssertionError

Error thrown by the runtime system when an assert statement fails.

CastError

Error thrown by the runtime system when a cast operation fails.

ConcurrentModificationError

Error occurring when a collection is modified during iteration. [...]

CyclicInitializationError

Error thrown when a lazily initialized variable cannot be initialized. [...]

Error

Error objects thrown in the case of a program failure. [...]

Exception

A marker interface implemented by all core library exceptions. [...]

FallThroughError

Error thrown when control reaches the end of a switch case. [...]

FormatException

Exception thrown when a string or some other data does not have an expected format and cannot be parsed or processed.

IndexError

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

IntegerDivisionByZeroException

NoSuchMethodError

Error thrown by the default implementation of noSuchMethod on Object.

NullThrownError

Error thrown when attempting to throw null. [...]

OutOfMemoryError

Error that the platform can use in case of memory shortage.

RangeError

Error thrown due to a value being outside a valid range.

StackOverflowError

Error that the platform can use in case of stack overflow.

StateError

The operation was not allowed by the current state of the object. [...]

TypeError

Error thrown by the runtime system when a dynamic type error happens.

UnimplementedError

Thrown by operations that have not been implemented yet. [...]

UnsupportedError

The operation was not allowed by the object. [...]