Can you explain what the 'lazy' keyword means in Dart language?

In Dart, the keyword lazy is used for lazy initialization of variables, meaning the variable's value is computed only upon the first access to it, not at the time of declaration.

This is useful when the computation of the value is resource-intensive or not always required, allowing for optimization of performance and memory usage.

An example using late and lazy (in Dart 3, the keyword late was introduced with lazy initialization):

late final String data = fetchData(); // fetchData() will be called upon the first access to data

String fetchData() {
  print('Calculating data');
  return 'Result';
}

void main() {
  print('Program started');
  print(data); // fetchData() is called here
  print(data); // The value is already computed, no second call occurs
}

Thus, lazy allows deferring computation until the moment it is actually needed.