在 Dart 中，有哪些循环操作？

• while
• do-while
• for
• for-in
• for-each
• map

while

int i = 1;
while (i <= 5) {
  print(i);
  i++;
}
// 1
// 2
// 3
// 4
// 5

do-while

int i = 1;
do {
  print(i);
  i++;
} while (i <= 5);
// 1
// 2
// 3
// 4
// 5

C 语言风格的 for 循环

const numbers = [1, 2, 3, 4, 5];
for (var i = 0; i < numbers.length; i++) {
  print(numbers[i]);
}
// 1
// 2
// 3
// 4
// 5

for-in 循环

const numbers = [1, 2, 3, 4, 5];
for (final number in numbers) {
  print(number);
}
// 1
// 2
// 3
// 4
// 5

for-each 循环

const numbers = [1, 2, 3, 4, 5];
numbers.forEach((number) => print(number));
// 1
// 2
// 3
// 4
// 5

for-each 底层实现也是使用了 for-in：

abstract class Iterable<E> {
  /// Invokes [action] on each element of this iterable in iteration order.
  void forEach(void action(E element)) {
    for (E element in this) action(element);
  }
}

map 循环

const numbers = [1, 2, 3, 4, 5];
final newNumbers = numbers.map((number) => number * number);
print(newNumbers);
// (1, 4, 9, 16, 25)