Dart Lesson 6 of 102 2 min read

Data Types in Dart: A Complete Overview

A tour of Dart's built-in data types: int, double, String, bool, List, Set, Map, Record, Null, Object and dynamic, with examples.

Every value in Dart has a type, and the type decides what you can do with the value. You can add two numbers, but you cannot add a number to a true.

The built-in types #

Seeing the types in action #

void main() {
  int apples = 12;
  double price = 4.5;
  String fruit = 'apple';
  bool inStock = true;
  List<String> colours = ['red', 'green'];
  Set<int> sizes = {1, 2, 3};
  Map<String, double> prices = {'apple': 4.5, 'pear': 6.0};
  (String, int) pair = ('apple', 12);

  print(apples.runtimeType);
  print(price.runtimeType);
  print(fruit.runtimeType);
  print(inStock.runtimeType);
  print(colours.runtimeType);
  print(pair.runtimeType);
  print('$sizes $prices');
}

int
double
String
bool
List<String>
(String, int)
{1, 2, 3} {apple: 4.5, pear: 6.0}

runtimeType tells you the type of a value while the program runs. It is handy for learning and debugging.

Everything is an object #

In Dart, numbers, strings, booleans and even functions are objects. That is why you can call methods directly on a value.

void main() {
  print(7.isEven);
  print(3.7.round());
  print('dart'.toUpperCase());
}

false
4
DART

Object and dynamic #

Object is the parent of every non-null type. A variable typed Object can hold any value, but Dart only lets you use what all objects share until you check the real type.

void main() {
  Object thing = 'a string';

  if (thing is String) {
    // Inside this block Dart knows it is a String.
    print(thing.length);
  }
}

8

dynamic also accepts anything, but turns checking off. Prefer Object when you truly need “any value”.

Checking a type with is #

void main() {
  var value = 3.5;
  print(value is double);
  print(value is num);
  print(value is! String);
}

true
true
true

Statically typed, with inference #

Dart checks types before running. If you write int x = 'hello'; the program will not start. You get this safety without typing much, because var infers the type for you.

Try it yourself #

Create one variable of each type in the table and print its runtimeType. What does print((1 + 2.0).runtimeType); show, and why?