Dart: lazily initialized class variable

readme.md

The example illustrates the following statement from The Dart Programming Language book (http://amzn.com/0321927702):

Class variables are initialized lazily; the initializer of a class variable is executed the first time its getter is invoked — that is, the first time one attempts to read the variable

When foo is printed the first time, its value is 0. Then we access the A.bar field and its initializer updates the foo's value. The second time we print foo its value is already 1.

Find the runnable version at DartPad.

main.dart

var foo = 0;

class A {
  static var bar = (foo = 1);
}

void main() {
  print(foo); // 0 since A.bar hasn't been ever accessed yet
  A.bar; // A.bar's initialization expression is lazily evaluated
  print(foo); // 1 since A.bar has been accessed already
}