dart:core

The dart:core library provides built-in types, collections, and other core functionality that forms the foundation of every Dart program. This library is automatically imported into every Dart file.

Overview

The dart:core library includes:

Built-in types (numbers, strings, booleans)
Collections (List, Set, Map, Iterable)
Date and time support
URI handling
Error and exception types
Core annotations and utilities

Numbers and Booleans

Integer and Double Types

int

class

Integer values with platform-dependent range. On native platforms, values can be from -2^63 to 2^63 - 1. On the web, integers are represented as JavaScript numbers.

double

class

Double-precision floating-point numbers as specified by the IEEE 754 standard.

num

abstract class

The base class for int and double. Provides common numeric operations.

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

// Numeric operations
int sum = 10 + 5;              // 15
double quotient = 10 / 3;      // 3.333...
int intDivision = 10 ~/ 3;     // 3
int remainder = 10 % 3;        // 1

Boolean Type

bool

class

The boolean type with two values: true and false.

Strings

String Class

String

class

An immutable sequence of UTF-16 code units. Strings are a core part of Dart and support both single and double quotes.

String shakespeareQuote = "All the world's a stage";
String multiLine = '''
  This is a
  multi-line
  string
''';

// String interpolation
var name = 'Dart';
var greeting = 'Hello, $name!';              // Hello, Dart!
var calculation = '1 + 1 = ${1 + 1}';        // 1 + 1 = 2

// String operations
var text = 'Hello World';
print(text.toLowerCase());                    // hello world
print(text.toUpperCase());                    // HELLO WORLD
print(text.contains('World'));                // true
print(text.split(' '));                       // ['Hello', 'World']
print(text.substring(0, 5));                  // Hello

StringBuffer

class

Efficiently builds strings incrementally. Use when concatenating many strings to avoid creating intermediate string objects.

var buffer = StringBuffer();
buffer.write('Hello');
buffer.write(' ');
buffer.write('World');
print(buffer.toString());  // Hello World

RegExp

class

Regular expressions for pattern matching in strings. Uses the same syntax as JavaScript regular expressions.

var numbers = RegExp(r'\d+');
var text = 'I have 2 cats and 3 dogs';
print(numbers.allMatches(text).map((m) => m.group(0)));  // (2, 3)

// Check if string matches pattern
var email = RegExp(r'^[\w-\.]+@[\w-]+\.[a-z]{2,}$');
print(email.hasMatch('[email protected]'));  // true

Collections

List

List<E>

abstract class

An ordered collection of objects with a length. Lists use zero-based indexing.

List API Details

// Creating lists
var superheroes = ['Batman', 'Superman', 'Wonder Woman'];
var numbers = <int>[1, 2, 3, 4, 5];
var fixedList = List<int>.filled(5, 0);       // [0, 0, 0, 0, 0]
var growableList = List<String>.empty(growable: true);

// Accessing elements
print(superheroes[0]);                         // Batman
print(superheroes.first);                      // Batman
print(superheroes.last);                       // Wonder Woman
print(superheroes.length);                     // 3

// Modifying lists
superheroes.add('Flash');
superheroes.addAll(['Aquaman', 'Cyborg']);
superheroes.remove('Batman');
superheroes.removeAt(0);
superheroes.insert(0, 'Green Lantern');

// List operations
var doubled = numbers.map((n) => n * 2).toList();
var evens = numbers.where((n) => n.isEven).toList();
var sum = numbers.reduce((a, b) => a + b);

Key methods:

add(E value) - Adds value to end
addAll(Iterable<E>) - Adds all values
insert(int index, E value) - Inserts at position
remove(Object value) - Removes first occurrence
removeAt(int index) - Removes at index
clear() - Removes all elements
sort([int compare(E a, E b)]) - Sorts in place

Set

Set<E>

abstract class

An unordered collection of unique objects. Sets automatically prevent duplicates.

Set API Details

// Creating sets
var villains = {'Joker', 'Lex Luthor'};
var emptySet = <String>{};
var fromList = Set<int>.from([1, 2, 2, 3, 3]);  // {1, 2, 3}

// Adding elements
villains.add('Joker');          // No effect, already exists
villains.add('Riddler');        // Added
print(villains.length);         // 3

// Set operations
var set1 = {1, 2, 3};
var set2 = {3, 4, 5};

print(set1.union(set2));         // {1, 2, 3, 4, 5}
print(set1.intersection(set2));  // {3}
print(set1.difference(set2));    // {1, 2}
print(set1.contains(2));         // true

Map

Map<K, V>

abstract class

An unordered collection of key-value pairs. Each key can occur only once.

Map API Details

// Creating maps
var sidekicks = {
  'Batman': 'Robin',
  'Superman': 'Lois Lane',
  'Spider-Man': 'Mary Jane'
};

var emptyMap = <String, int>{};
var scores = Map<String, int>();

// Accessing values
print(sidekicks['Batman']);              // Robin
print(sidekicks['Unknown']);             // null
print(sidekicks.containsKey('Batman'));  // true

// Modifying maps
sidekicks['Wonder Woman'] = 'Steve Trevor';
sidekicks.remove('Superman');
sidekicks.clear();

// Iterating
var capitals = {'USA': 'Washington', 'France': 'Paris'};
capitals.forEach((country, city) {
  print('Capital of $country is $city');
});

// Map operations
var keys = capitals.keys;        // ('USA', 'France')
var values = capitals.values;    // ('Washington', 'Paris')
var entries = capitals.entries;  // (MapEntry('USA', 'Washington'), ...)

Key methods:

operator [](K key) - Gets value for key
operator []=(K key, V value) - Sets value for key
putIfAbsent(K key, V ifAbsent()) - Adds if key absent
remove(K key) - Removes entry
containsKey(K key) - Checks for key
containsValue(V value) - Checks for value

Iterable

Iterable<E>

abstract class

A collection of values that can be accessed sequentially. Base interface for List and Set.

var numbers = [1, 2, 3, 4, 5];

// Transform operations
var doubled = numbers.map((n) => n * 2);           // (2, 4, 6, 8, 10)
var evens = numbers.where((n) => n.isEven);        // (2, 4)
var expanded = numbers.expand((n) => [n, n]);      // (1, 1, 2, 2, 3, 3, ...)

// Reduction operations
var sum = numbers.reduce((a, b) => a + b);         // 15
var product = numbers.fold(1, (a, b) => a * b);    // 120

// Testing
var hasEven = numbers.any((n) => n.isEven);        // true
var allPositive = numbers.every((n) => n > 0);     // true

// Element access
var first = numbers.first;                          // 1
var last = numbers.last;                            // 5
var firstEven = numbers.firstWhere((n) => n.isEven); // 2

Date and Time

DateTime

class

Represents an instant in time. Can work with both UTC and local time zones.

// Current time
var now = DateTime.now();
var utcNow = DateTime.now().toUtc();

// Creating specific dates
var birthday = DateTime(1995, 5, 15);
var meeting = DateTime(2024, 3, 1, 14, 30);  // 2:30 PM

// Parsing dates
var parsed = DateTime.parse('2024-03-01 14:30:00');

// Date arithmetic
var tomorrow = now.add(Duration(days: 1));
var lastWeek = now.subtract(Duration(days: 7));
var difference = tomorrow.difference(now);  // Duration

// Comparisons
if (birthday.isBefore(now)) {
  print('Birthday has passed');
}

Duration

class

Represents a span of time, such as 3 days or 2 hours.

var duration = Duration(
  days: 1,
  hours: 12,
  minutes: 30,
  seconds: 45,
);

print(duration.inDays);      // 1
print(duration.inHours);     // 36
print(duration.inMinutes);   // 2190

// Duration arithmetic
var longer = duration + Duration(hours: 6);
var shorter = duration - Duration(minutes: 30);
var doubled = duration * 2;

URI

Uri

class

Represents a Uniform Resource Identifier. Used for URLs and URIs.

// Parsing URIs
var uri = Uri.parse('https://example.com/path?query=value#fragment');

print(uri.scheme);      // https
print(uri.host);        // example.com
print(uri.path);        // /path
print(uri.query);       // query=value
print(uri.fragment);    // fragment

// Building URIs
var built = Uri(
  scheme: 'https',
  host: 'api.example.com',
  path: '/users',
  queryParameters: {'page': '1', 'limit': '10'},
);
print(built);  // https://api.example.com/users?page=1&limit=10

// Encoding/decoding
var encoded = Uri.encodeComponent('hello world');  // hello%20world
var decoded = Uri.decodeComponent('hello%20world'); // hello world

Errors and Exceptions

Exception Types

Common Exception Types

Exception

abstract class

Base class for application-level errors that are intended to be caught.

Error

class

Base class for programming errors that should typically not be caught.

Common exceptions:

FormatException - Invalid string format
RangeError - Value out of valid range
ArgumentError - Invalid argument to function
StateError - Invalid object state
UnsupportedError - Unsupported operation

// Throwing exceptions
throw FormatException('Invalid email format');
throw ArgumentError.value(value, 'age', 'Must be positive');

// Custom exceptions
class NetworkException implements Exception {
  final String message;
  NetworkException(this.message);
  
  @override
  String toString() => 'NetworkException: $message';
}

Symbols and Annotations

Common Annotations

@deprecated

annotation

Marks a declaration as deprecated. Causes warnings when used.

@override

annotation

Indicates that a member overrides a superclass member.

class Example {
  @deprecated
  void oldMethod() {
    // This method is deprecated
  }
  
  @override
  String toString() => 'Example instance';
}

Platform Detection

Check platform at compile time:

import 'dart:io' show Platform;

void checkPlatform() {
  if (Platform.isLinux) {
    print('Running on Linux');
  } else if (Platform.isMacOS) {
    print('Running on macOS');
  } else if (Platform.isWindows) {
    print('Running on Windows');
  }
}

Best Practices

Use const constructors when creating compile-time constants
Prefer final for variables that won’t change
Use type annotations for public APIs
Leverage collection literals ([], {}, <>[]) over constructors

The dart:core library is optimized and fundamental to Dart. Understanding these core types and collections is essential for writing idiomatic Dart code.

dart:collection - Additional collection types
dart:convert - JSON and other encoders/decoders
dart:math - Mathematical functions and constants

Getting Started

Building the SDK

Core Concepts

Compilers

Core Libraries

Runtime & VM

Tools & CLI

Development

Overview

Numbers and Booleans

Integer and Double Types

Boolean Type

Strings

String Class

StringBuffer

RegExp

Collections

List

Set

Map

Iterable

Date and Time

DateTime

Duration

URI

Errors and Exceptions

Exception Types

Symbols and Annotations

Common Annotations

Platform Detection

Best Practices

Build docs developers (and LLMs) love

Getting Started

Building the SDK

Core Concepts

Compilers

Core Libraries

Runtime & VM

Tools & CLI

Development

​Overview

​Numbers and Booleans

​Integer and Double Types

​Boolean Type

​Strings

​String Class

​StringBuffer

​RegExp

​Collections

​List

​Set

​Map

​Iterable

​Date and Time

​DateTime

​Duration

​URI

​Errors and Exceptions

​Exception Types

​Symbols and Annotations

​Common Annotations

​Platform Detection

​Best Practices

​Related Libraries

Build docs developers (and LLMs) love

Overview

Numbers and Booleans

Integer and Double Types

Boolean Type

Strings

String Class

StringBuffer

RegExp

Collections

List

Set

Map

Iterable

Date and Time

DateTime

Duration

URI

Errors and Exceptions

Exception Types

Symbols and Annotations

Common Annotations

Platform Detection

Best Practices

Related Libraries