[WIP] Port of redux-saga to Dart

日本語

Redux-saga for dart.

This library supports invocation and collaboration of isolates based on channel of action.

Integrated with dart-redux are planned.

dart-saga (and redux-saga) is a library that aims to make application side effects (i.e. asynchronous things like data fetching and impure things like accessing the browser cache) easier to manage, more efficient to execute, simple to test, and better at handling failures.

redux-saga uses co-routine with generator function as a concurrency basis but this library uses isolates insteads and streams. so implementation is very simple and suit with Dart way.

Dart-saga can be regarded as a library that abstracts and hides low-level dart isolates and streaming operations.

Note: This package is still under development, and many of functionality might not be available yet. Feedback and Pull Requests are most welcome!

Sample code

import "dart:async";
import 'package:dart_saga/dart_saga.dart';

rootSaga([msg, greeting]) async* {
  print("rootSaga(${msg}) started greeting: ${greeting}");
  Completer<int> saga2handle = new Completer();
  yield fork(saga2, ["start saga2"], saga2handle);

  for (int i = 0; i < 10; i++) {
    yield delay(1000);
    if (i == 5) {
      yield cancel(await saga2handle.future);
    }
  }
}

saga2([msg]) async* {
  print("           saga2(${msg}) started");
  Completer<int> saga3handle;
  yield fork(saga3, ["start saga3"], saga3handle);

  for (int i = 0; true; i++) {
    print("           saga2");
    yield delay(1000);
    yield put(Action("HOGE", "From saga2"));
    if (i == 3) {
      yield cancel(await saga3handle.future);
    }
  }
}

saga3([msg]) async* {
  print("                      saga3(${msg}) started");
  while (true) {
    print("                      saga3");
    Completer takenAction = new Completer();
    yield take("HOGE", takenAction);
    print("                      taken ${await takenAction.future}");
  }
}

main() {
  var effectManager = new EffectManager();
  effectManager.run(rootSaga, ["start rootSaga", "hello"]);
}

Demo

% pub run example/simple_demo.dart
start _isolate context
Task.start 0
rootSaga(start rootSaga) started greeting: hello
Task.start 1
           saga2(start saga2) started
           saga2
Task.start 2
                      saga3(start saga3) started
                      saga3
           saga2
                      taken Action(HOGE, From saga2)
                      saga3
           saga2
                      taken Action(HOGE, From saga2)
                      saga3
           saga2
                      taken Action(HOGE, From saga2)
                      saga3
Task(taskId=2) terminated: null.
Task(taskId=1) terminated: null.
Task(taskId=0) terminated: null.

Implemented Redux-Saga's Effects

• take
• takeMaybe
• put
• putResolve
• all
• race
• call
• apply
• cps
• fork
• spawn
• join
• cancel
• select
• actionChannel
• cancelled
• flush
• getContext
• setContext,
• retry
• takeEvery
• takeLatest
• takeLeading
• throttle
• delay

Restrictions

Yield is statement, not expression

Dart's generator/async generator lacks ability to return value from yield constructs. In both of ES2015 and Python, yield is an expression, but in Dart, it's statement, so we cannot get any value from effect directly.

In this library, instead, you have to use completer.

e.g.

In the case you want to write:

  int sagaHandle = yield fork(saga2, []);

You have to write:

  Completer<int> sagaHandle = new Completer();
  yield fork(saga2, [], sagaHandle);

Protection between Isolates

It is not possible to cross Isolates, share a Completer and fire a Future.