Runner constructor

Create a Runner instance with an empty cache.

The optional wrapRunStep parameters allows specification of a function that will wrap the runStep methods provided in the Step definitons. This can be used to catch exceptions, run steps in a zone, measure execution time of a step (excluding dependencies), or simply log step execution as illustrated in the example below.

/// Define a step that return 'Hello World!'
final helloWorldStep = Step.define('hello-world').build(() => 'Hello World!');

/// Define a step that depends on helloWorldStep and prints its return
/// value.
final Step<void> printStep = Step.define('print-msg')
    // Declare dependency on helloWorldStep
    .dep(helloWorldStep)
    // Build step, result from helloWorldStep will be passed in as `msg`
    .build((msg) {
  print(msg);
});

/// Implementation of [RunStepWrapper] that logs start and finish for
/// each step.
Future<T> wrapStepWithLogging<T>(
  Step<T> step,
  Future<T> Function() runStep,
) async {
  print('Starting to run ${step.name}');
  try {
    return await runStep();
  } finally {
    print('Finishing running ${step.name}');
  }
}

Future<void> main() async {
  // This creates a Runner that will wrap calls to runStep with
  // wrapStepWithLogging, hence, printing log entries for step execution.
  final r = Runner(wrapRunStep: wrapStepWithLogging);
  await r.run(printStep);
}

Implementation

Runner class