Dart's lazy initialization in action.

lazy.dart

var potatoSack = [];
var potato = buildPotato();

String buildPotato() {
  var tater = 'a delicious potato';
  potatoSack.add(tater);
  return tater;
} 

void main() {
  print(potatoSack); //output is [] (empty array)
  print(potato); // now calls buildPotato();
  print(potatoSack); // output is ['a delicious potato']
}