.DART File Format

Introduction

A .dart file holds source code in Dart, the language Google announced in 2011. It compiles to native machine code and to JavaScript and WebAssembly, and is best known as the language of the Flutter interface toolkit.

A project is described by a pubspec.yaml file, which names its packages from the pub.dev repository. Application code usually sits under lib/.

Structure

A Dart file is UTF-8 text. Each file is normally a library of its own, and a file that starts with part of belongs to another. import lines come first, with URIs such as dart:io for the core libraries and package:path/path.dart for packages. After them come classes, functions and variables, all allowed at the top level. A program starts at main().

Names beginning with an underscore are private to their library. Statements end with semicolons. Comments are //, /* */ and /// for documentation. A type can hold null only if it is marked with ?, as in String?.

import 'dart:math';

class Point {
  final double x, y;
  const Point(this.x, this.y);

  double get distance => sqrt(x * x + y * y);
}

void main() {
  final p = Point(3, 4);
  print('Distance: ${p.distance}');
}

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