[번역/요약] Dart Language samples

1. Hello World

void main(){
    print('Hello, World!');
}

2. 변수 / Variables

var name = 'Voyager I';
var year = 1977;
var antennaDiameter = 3.7;
var flybyObjects = ['Jupiter', 'Saturn', 'Uranus', 'Neptune'];
var image = {
    'tags':['saturn'],
    'url':'//path/to/saturn.jpg'
};

3. 흐름 제어문 / Control flow statements

if(year >= 2001){
    print('21st century');
}
else if(year >= 1901){
    print('20th century');
}

for(var object in flyByObjects){
    print(object);
}

for(int month = 1; month <= 12; month++){
    print(month);
}

while(year < 2016){
    year += 1;
}

4. 함수 / Functions

int fibonacci(int n)
{
    if(n == 0 || n == 1) return n;
    return fibonacci(n - 1) + finbonacci(n - 2);

}

var result = fibonacci(20);

flyByObjects.where((name) => name.contains('turn')).forEach(print);

5. 주석 / Comments

// This is a normal, one-line comment.

/// This is a documentation comment, used to document libraries,
/// classes, and their members. Tools like IDEs and dartdoc treat
/// doc comments specially.

/* Comments like these are also supported. */

6. Imports

// Importing core libraries
import 'dart:math';

// Importing libraries from external packages
import 'package:test/test.dart';

// Importing files
import 'path/to/my_other_file.dart';

7. 클래스 / Classes

class Spacecraft {
  String name;
  DateTime launchDate;

  // 생성자입니다. 멤버에 값을 할당하는 약간의 syntactic sugar를 사용합니다.
  Spacecraft(this.name, this.launchDate) {
    // 초기화 코드는 여기에 옵니다.
  }

  // 이름 있는 생성자는 기본 생성자에 추가적인 기능을 더합니다.
  Spacecraft.unlaunched(String name) : this(name, null);

  int get launchYear =>
      launchDate?.year; // final이 아닌 읽기 전용 속성

  // 메소드.
  void describe() {
    print('Spacecraft: $name');
    if (launchDate != null) {
      int years =
          DateTime.now().difference(launchDate).inDays ~/
              365;
      print('Launched: $launchYear ($years years ago)');
    } else {
      print('Unlaunched');
    }
  }
}

// 클래스 사용 예
var voyager = Spacecraft('Voyager I', DateTime(1977, 9, 5));
voyager.describe();

var voyager3 = Spacecraft.unlaunched('Voyager III');
voyager3.describe();

8. 상속 / Inheritance

class Orbiter extends Spacecraft {
  num altitude;
  Orbiter(String name, DateTime launchDate, this.altitude)
      : super(name, launchDate);
}

9. 믹스인 / Mixins

class Piloted {
  int astronauts = 1;
  void describeCrew() {
    print('Number of astronauts: $astronauts');
  }
}

class PilotedCraft extends Spacecraft with Piloted {
  // ···
}

10. 인터페이스와 추상 클래스 / interfaces and abstract classes

class MockSpaceship implements Spacecraft {
  // ···
}

abstract class Describable {
  void describe();

  void describeWithEmphasis() {
    print('=========');
    describe();
    print('=========');
  }
}

11. Async

const oneSecond = Duration(seconds: 1);
// ···
Future<void> printWithDelay(String message) async {
  await Future.delayed(oneSecond);
  print(message);
}

Future<void> printWithDelay(String message) {
  return Future.delayed(oneSecond).then((_) {
    print(message);
  });
}

Future<void> createDescriptions(Iterable<String> objects) async {
  for (var object in objects) {
    try {
      var file = File('$object.txt');
      if (await file.exists()) {
        var modified = await file.lastModified();
        print(
            'File for $object already exists. It was modified on $modified.');
        continue;
      }
      await file.create();
      await file.writeAsString('Start describing $object in this file.');
    } on IOException catch (e) {
      print('Cannot create description for $object: $e');
    }
  }
}

Stream<String> report(Spacecraft craft, Iterable<String> objects) async* {
  for (var object in objects) {
    await Future.delayed(oneSecond);
    yield '${craft.name} flies by $object';
  }
}

12. 예외 / Exceptions

if(astronauts == 0){
    throw StateError('No astronauts.');
}

try
{
    for(var object in flyByObjects){
        var description = await File('$object.txt').readAsString();
        print(description);
    }
} on IOException catch (e){
    print('Could not describe object: $e');
} finally{
    flyByObjects.clear();
}