log method

System<State, Event> log({
  1. String? label,
  2. void print(
    1. String message
    )?,
})

Add log effect to the system.

After apply this operator, system will print message when:

  • system run
  • system update state
  • system dispose

For example:

System<int, CounterEvent> createCounterSystem() { ... }

void main() async {

  final counterSystem = createCounterSystem();

  final disposer = counterSystem
    .log()  // --> add log effect
    .run();
  
  await Future<void>.delayed(const Duration(seconds: 6));

  disposer();

}

will log something like this:

System<int, CounterEvent> Run
System<int, CounterEvent> Update {
  event: null
  oldState: null
  state: 0
}
System<int, CounterEvent> Update {
  event: Instance of 'Increment'
  oldState: 0
  state: 1
}
System<int, CounterEvent> Dispose

If we want to replace the runtimeType System<int, CounterEvent> text with some meaningful label, we can use label parameter:

  counterSystem
    .log(label: 'CounterSystem')
    .run();

the output will become:

CounterSystem Run
CounterSystem Update {
  event: null
  oldState: null
  state: 0
}
CounterSystem Update {
  event: Instance of 'Increment'
  oldState: 0
  state: 1
}
CounterSystem Dispose

By default log operator use built in print function (from ''dart:core'') to print message, but we can provide custom print function (eg, debugPrint, logger.log) to replace it:

  counterSystem
    .log(print: (message) => debugPrint(message))
    .run();

The message will be print with debugPrint in the above example.

Implementation

/// ```
/// CounterSystem Run
/// CounterSystem Update {
///   event: null
///   oldState: null
///   state: 0
/// }
/// CounterSystem Update {
///   event: Instance of 'Increment'
///   oldState: 0
///   state: 1
/// }
/// CounterSystem Dispose
/// ```
///
/// By default `log` operator use built in `print` function (from ''dart:core'') to print message,
/// but we can provide custom [print] function (eg, `debugPrint`, `logger.log`) to replace it:
///
/// ```dart
///   counterSystem
///     .log(print: (message) => debugPrint(message))
///     .run();
/// ```
///
/// The message will be print with `debugPrint` in the above example.
///
System<State, Event> log({
  core.String? label,
  void Function(core.String message)? print,
}) {
  final localLabel = label ?? '$runtimeType';
  final localPrint = print ?? (core.String message) => core.print(message);
  // ignore: unnecessary_this
  return this
    .add(effect: (state, oldState, event, _) {
      if (event == null) localPrint('$localLabel Run');
      localPrint('$localLabel Update {\n  event: $event\n  oldState: $oldState\n  state: $state\n}');
     })
    .onDispose(run: () {
      localPrint('$localLabel Dispose');
    });
}