What does .. means in dart language?-CodePudding

What does .. mean in dart language in flutter projects?

consider following examples:

@override
void initState() {
  super.initState();
  _controller = AnimationController(
    duration: const Duration(milliseconds: 1000),
    vsync: this
  )..repeat();
// ^^ here

CodePudding user response：

It is called cascade operator, which can be read about in official doc

In simple form, it says that invoke that method, but instead of returning the return value of method return the reference for the object (class), it is invoked on.

Here although repeat is going to run on AnimationController it will return the AnimationController reference to be stored in _controller. It allows to access and invoke another method of AnimationController in other parts that got access to _controller

CodePudding user response：

Its called cascade operator

You can set properties like this

For Example, You can use cascade operator like this, It improves readability

class User {
  
  double? id;
  
  String? name;
  
}

  User user = User();
  user.id = 5;
  user.name = 'Maverick';
  
  User user2 = User();
  user2
    ..id = 6
    ..name = 'Kenny';
  
  User user3 = User()..id = 7
                     ..name = 'Roger';
  
  print(user3.name); // prints Roger