在 Dart 中混合初始化器和构造器主体

Question

I know that you can initialize final variables in a class with something like:

class A {
  final num x;
  final num y;
  final num d;

  A(this.x, this.y): 
    d = sqrt(pow(x, 2) + pow(y, 2));
}

And you can create regular variables inside a constructor like this:

class A {
  String z;

  A(){
    z = 'hello';
  }
}

But how do you mix both? Is it possible? What is the syntax?

Answer 1

Simply continue with the constructor right after the initializer, but, since you're going to use curly brackets ( {} ), you shouldn't use the semi-colon ( ; ):

class A {
  final num x;
  final num y;
  final num d;
  String z;

  A(this.x, this.y) 
    : d = sqrt(pow(x, 2) + pow(y, 2))
  {
    z = 'hello';
  }
}