Dart | 语法

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yaotao 9月 15, 2021

【Dart语法】

一、Hello, World!

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

二、函数的使用

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// A function declaration.
int timesTwo(int x) {
  return x * 2;
}

// Arrow syntax is shorthand for `{ return expr; }`.
int timesFour(int x) => timesTwo(timesTwo(x));

// Functions are objects.
int runTwice(int x, int Function(int) f) {
  for (var i = 0; i < 2; i++) {
    x = f(x);
  }
  return x;
}

void main() {
  print('4 times two is ${timesTwo(4)}');
  print('4 times four is ${timesFour(4)}');
  print('2 x 2 x 2 is ${runTwice(2, timesTwo)}');
}

三、List使用、函数控制

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bool isEven(int x) {
  // An if-else statement.
  if (x % 2 == 0) {
    return true;
  } else {
    return false;
  }
}

List<int> getEvenNumbers(Iterable<int> numbers) {
  var evenNumbers = <int>[];

  // A for-in loop.
  for (var i in numbers) {
    // A single line if statement.
    if (isEven(i)) {
      evenNumbers.add(i);
    }
  }

  return evenNumbers;
}

void main() {
  var numbers = List.generate(10, (i) => i);
  print(getEvenNumbers(numbers));
}

四、库的导入 、 Strings

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import 'dart:math' as math;

void main() {
  print('a single quoted string');
  print("a double quoted string");

  // Strings can be combined by placing them adjacent to each other.
  print('cat' 'dog');

  // Triple quotes define a multi-line string.
  print('''triple quoted strings
are for multiple lines''');

  // Dart supports string interpolation.
  final pi = math.pi;
  print('pi is $pi');
  print('tau is ${2 * pi}');
}

五、数组、枚举、结构体

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// A list literal.
const lostNumbers = [4, 8, 15, 16, 23, 42];

// A map literal.
const nobleGases = {
  'He': 'Helium',
  'Ne': 'Neon',
  'Ar': 'Argon',
};

// A set literal.
const frogs = {
  'Tree',
  'Poison dart',
  'Glass',
};

void main() {
  print(lostNumbers.last);
  print(nobleGases['Ne']);
  print(frogs.difference({'Poison dart'}));
}

六、Class

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// Abstract classes can't be instantiated.
abstract class Item {
  void use();
}

// Classes can implement other classes.
class Chest<T> implements Item {
  final List<T> contents;

  // Constructors can assign arguments to instance variables using `this`.
  Chest(this.contents);

  @override
  void use() => print('$this has ${contents.length} items.');
}

class Sword implements Item {
  int get damage => 5;

  @override
  void use() => print('$this dealt $damage damage.');
}

// Classes can extend other classes.
class DiamondSword extends Sword {
  @override
  final int damage = 50;
}

void main() {
  // The 'new' keyword is optional.
  var chest = Chest<Item>([
    DiamondSword(),
    Sword(),
  ]);

  chest.use();

  for (final item in chest.contents) {
    item.use();
  }
}