dart:core library Null safety

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.

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

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

String philosophy = 'Live on ';
String get palindrome => philosophy + philosophy.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 string of one or more digits:

var numbers = new 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.

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

A Set is an unordered collection of unique objects. You cannot get an item by index (position). Adding a duplicate item has no effect.

Set villains = new Set();
villains.add('Joker');
villains.addAll( ['Lex Luther', 'Voldemort'] );

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

Map 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 length.

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.

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

Create a Duration object specifying the individual time units.

Duration timeRemaining = new 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 on the web.

Uri 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.