基本类型

1、将字符串转换为数字或将数字转换为字符串的方法：

// String -> int
var one = int.parse('1');
assert(one == 1);

// String -> double
var onePointOne = double.parse('1.1');
assert(onePointOne == 1.1);

// int -> String
String oneAsString = 1.toString();
assert(oneAsString == '1');

// double -> String
String piAsString = 3.14159.toStringAsFixed(2);
assert(piAsString == '3.14');

2、文字数字是编译时常量。许多算术表达式也是编译时常量，只要它们的操作数是计算结果为数字的编译时常量。

const msPerSecond = 1000;
const secondsUntilRetry = 5;
const msUntilRetry = secondsUntilRetry * msPerSecond;

3、创建多行字符串，请使用带有单引号或双引号的三重引号：

var s1 = '''
You can create
multi-line strings like this one.
''';

var s2 = """This is also a
multi-line string.""";