Dart is a true object-oriented language,so even functions are objects and have a type,Function. This means that functions can be assigned to variables or passed as arguments to other functions. You can also call an instance of a Dart class as if it were a function.

Dart的function可以声明返回值在函数声明的时候也可以也不要. bool isNoble(atomicNumber) { return _nobleGases[atomicNumber] != null; }

isNoble(atomicNumber) {return _nobleGases[atomicNumber] != null;
}

For functions that contain just one expression, you can use a shorthand syntax: => The => expr syntax is a shorthand for { return expr; }.

bool isNoble(int atomicNumber) => _nobleGases[atomicNumber] != null;

A function can have two types of parameters: required and optional. The required parameters are listed first,followed by any optional parameters. Named optional parameters can also be marked as @required.

enableFlags(bold:true,hidden:false);

Optional positional parameters Wrapping a set of function parameters in [] marks them as optional positional parameters:

String say(String from, String msg, [String device]) {var result = '$from says $msg';if (device != null) {result = '$result with a $device';}return result;
}

Default parameter values Your function can use = to define default values for both named and positional parameters. The default values must be compile-time constants. If no default value is provided, the default value is null. 可以给函数参数指定默认值,通过=指定.

void enableFlags({bool bold = false, bool hidden = false}) {...}

甚至可以给函数参数传递默认的list或者map.

void doStuff
(
{List<int> list = const [1, 2, 3],
Map<String, String> gifts = const {'first': 'paper','second': 'cotton','third': 'leather'
}})
{print('list:  $list');print('gifts: $gifts');
}

The .. syntax in the preceding code is called a cascade. With cascades, you can perform multiple operations on the members of a single object. 这个有点像kotlin的apply函数.