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Published 9 months ago • verified publishernosy.dev• Latest: 1.0.0
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A reactive primitive and simple state managerment solution for dart.

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Overview #

A Beacon is a reactive primitive(signal) and simple state management solution for Dart and Flutter.

Note

This is the pure dart package. For the flutter package, see state_beacon

Installation #

dart pub add state_beacon

Usage #

void main() {
  final name = Beacon.writable("Bob");
  final age = Beacon.writable(20);
  final college = Beacon.writable("MIT");

  Beacon.effect(() {
    var msg = '${name.value} is ${age.value} years old';

    if (age.value > 21) {
      msg += ' and can go to ${college.value}';
    }
    print(msg);
  });

  // prints "Alice is 20 years old"
  name.value = "Alice";

  // prints "Alice is 21 years old"
  age.value = 21;

  // prints "Alice is 21 years old"
  college.value = "Stanford";

  // prints "Alice is 22 years old and can go to Stanford"
  age.value = 22;

  // prints "Alice is 22 years old and can go to Harvard"
  college.value = "Harvard";
}

Linting (optional) #

It is recommended to use state_beacon_lint for package specific rules.

dart pub add custom_lint state_beacon_lint --dev

Enable the custom_lint plugin in your analysis_options.yaml file by adding the following.

analyzer:
    plugins:
        - custom_lint

NB: Create the file if it doesn't exist.

Features #

Pitfalls

Beacon.writable: #

Creates a WritableBeacon from a value that can be read and written to.

final counter = Beacon.writable(0);
counter.value = 10;
print(counter.value); // 10

Beacon.lazyWritable: #

Like Beacon.writable but behaves like a late variable. It must be set before it's read.

NB: All writable beacons have a lazy counterpart.

final counter = Beacon.lazyWritable();

print(counter.value); // throws UninitializeLazyReadException()

counter.value = 10;
print(counter.value); // 10

Beacon.scopedWritable: #

Returns a ReadableBeacon and a function for setting its value. This is useful for creating a beacon that's readable by the public, but writable only by the owner.

var (count,setCount) = Beacon.scopedWritable(15);

Beacon.readable: #

Creates an immutable ReadableBeacon from a value. This is useful for exposing a beacon's value to consumers without allowing them to modify it.

final counter = Beacon.readable(10);
counter.value = 10; // Compilation error


final _internalCounter = Beacon.writable(10);

// Expose the beacon's value without allowing it to be modified
ReadableBeacon<int> get counter => _internalCounter;

Beacon.effect: #

An effect is just a function that will re-run whenever one of its dependencies change. An effect runs immediately after creation.

final age = Beacon.writable(15);

Beacon.effect(() {
    if (age.value >= 18) {
      print("You can vote!");
    } else {
       print("You can't vote yet");
    }
 });

// Outputs: "You can't vote yet"

age.value = 20; // Outputs: "You can vote!"

Beacon.batch: #

This allows multiple updates to be batched into a single update. This can be used to optimize performance by reducing the number of update notifications.

final age = Beacon.writable<int>(10);

var callCount = 0;

age.subscribe((_) => callCount++);

Beacon.batch(() {
  age.value = 15;
  age.value = 16;
  age.value = 20;
  age.value = 23;
});

expect(callCount, equals(1)); // There were 4 updates, but only 1 notification

Beacon.derived: #

Creates a DerivedBeacon whose value is derived from a computation function. This beacon will recompute its value every time one of it's dependencies change.

Example:

final age = Beacon.writable<int>(18);
final canDrink = Beacon.derived(() => age.value >= 21);

print(canDrink.value); // Outputs: false

age.value = 22;

print(canDrink.value); // Outputs: true

Beacon.derivedFuture: #

Creates a DerivedBeacon whose value is derived from an asynchronous computation. This beacon will recompute its value every time one of its dependencies change. The result is wrapped in an AsyncValue, which can be in one of four states: idle, loading, data, or error.

If manualStart is true (default: false), the beacon will be in the idle state and the future will not execute until [start()] is called.

If cancelRunning is true (default: true), the results of a current execution will be discarded if another execution is triggered before the current one finishes.

Example:

final counter = Beacon.writable(0);

// The future will be recomputed whenever the counter changes
final derivedFutureCounter = Beacon.derivedFuture(() async {
  final count = counter.value;
  await Future.delayed(Duration(seconds: count));
  return '$count second has passed.';
});

class FutureCounter extends StatelessWidget {
const FutureCounter({super.key});

@override
Widget build(BuildContext context) {
  return switch (derivedFutureCounter.watch(context)) {
    AsyncData<String>(value: final v) => Text(v),
    AsyncError(error: final e) => Text('$e'),
    AsyncLoading() || AsyncIdle() => const CircularProgressIndicator(),
  };
}
}

Can be transformed into a future with myFutureBeacon.toFuture() This can useful when a DerivedFutureBeacon depends on another DerivedFutureBeacon. This functionality is also available to regular FutureBeacons and StreamBeacons.

var count = Beacon.writable(0);

var firstName = Beacon.derivedFuture(() async {
  final val = count.value;
  await Future.delayed(k10ms);
  return 'Sally $val';
});

var lastName = Beacon.derivedFuture(() async {
  final val = count.value + 1;
  await Future.delayed(k10ms);
  return 'Smith $val';
});

var fullName = Beacon.derivedFuture(() async {
  // wait for the future to complete
  // we don't have to manually handle all the states
  final [fname, lname] = await Future.wait(
    [
      firstName.toFuture(),
      lastName.toFuture(),
    ],
  );

  return '$fname $lname';
});

Beacon.debounced: #

Creates a DebouncedBeacon that will delay updates to its value based on the duration. This is useful when you want to wait until a user has stopped typing before performing an action.

var query = Beacon.debounced('', duration: Duration(seconds: 1));

query.subscribe((value) {
  print(value); // Outputs: 'apple' after 1 second
});

// simulate user typing
query.value = 'a';
query.value = 'ap';
query.value = 'app';
query.value = 'appl';
query.value = 'apple';

// after 1 second, the value will be updated to 'apple'

Beacon.throttled: #

Creates a ThrottledBeacon that will limit the rate of updates to its value based on the duration.

If dropBlocked is true(default), values will be dropped while the beacon is blocked, otherwise, values will be buffered and emitted one by one when the beacon is unblocked.

const k10ms = Duration(milliseconds: 10);
var beacon = Beacon.throttled(10, duration: k10ms);

beacon.set(20);
expect(beacon.value, equals(20)); // first update allowed

beacon.set(30);
expect(beacon.value, equals(20)); // too fast, update ignored

await Future.delayed(k10ms * 1.1);

beacon.set(30);
expect(beacon.value, equals(30)); // throttle time passed, update allowed

Beacon.filtered: #

Creates a FilteredBeacon that will only updates its value if it passes the filter criteria. The filter function receives the previous and new values as arguments. The filter function can also be changed using the setFilter method.

Simple Example:

// only positive values are allowed
var pageNum = Beacon.filtered(10, filter: (prev, next) => next > 0);
pageNum.value = 20; // update is allowed
pageNum.value = -5; // update is ignored

Example when filter function depends on another beacon:

In this example, posts is a derived future beacon that will fetch the posts whenever pageNum changes. We want to prevent the user from changing pageNum while posts is loading.

var pageNum = Beacon.filtered(1); // we will set the filter function later

final posts = Beacon.derivedFuture(() => Repository.getPosts(pageNum.value));

// can't change pageNum while loading
pageNum.setFilter((prev, next) => !posts.isLoading);

Extracted from the infinite list example

Beacon.timestamped: #

Creates a TimestampBeacon that attaches a timestamp to each value update.

var myBeacon = Beacon.timestamped(10);
print(myBeacon.value); // Outputs: (value: 10, timestamp: __CURRENT_TIME__)

Beacon.undoRedo: #

Creates an UndoRedoBeacon that allows undoing and redoing changes to its value.

var age = Beacon.undoRedo(0, historyLimit: 10);

age.value = 10;
age.value = 20;

age.undo(); // Reverts to 10
age.redo(); // Goes back to 20

Beacon.bufferedCount: #

Creates a BufferedCountBeacon that collects and buffers a specified number of values. Once the count threshold is reached, the beacon's value is updated with the list of collected values and the buffer is reset.

This beacon is useful in scenarios where you need to aggregate a certain number of values before processing them together.

var countBeacon = Beacon.bufferedCount<int>(3);

countBeacon.subscribe((values) {
  print(values);
});

countBeacon.add(1);
countBeacon.add(2);
countBeacon.add(3); // Triggers update and prints [1, 2, 3]

You may also access the currentBuffer as a readable beacon. See it in use in the konami example;

Beacon.bufferedTime: #

Creates a BufferedTimeBeacon that collects values over a specified time duration. Once the time duration elapses, the beacon's value is updated with the list of collected values and the buffer is reset.

var timeBeacon = Beacon.bufferedTime<int>(duration: Duration(seconds: 5));

timeBeacon.subscribe((values) {
  print(values);
});

timeBeacon.add(1);
timeBeacon.add(2);
// After 5 seconds, it will output [1, 2]

Beacon.stream: #

Creates a StreamBeacon from a given stream. This beacon updates its value based on the stream's emitted values. The emitted values are wrapped in an AsyncValue, which can be in one of three states: loading, data, or error. This can we wrapped in a Throttled or Filtered beacon to control the rate of updates. Can be transformed into a future with mystreamBeacon.toFuture():

var myStream = Stream.periodic(Duration(seconds: 1), (i) => i);

var myBeacon = Beacon.stream(myStream);

myBeacon.subscribe((value) {
  print(value); // Outputs AsyncLoading(),AsyncData(0),AsyncData(1),AsyncData(2),...
});

Beacon.streamRaw: #

Like Beacon.stream, but it doesn't wrap the value in an AsyncValue. If you don't supply an initial value, the type has to be nullable.

var myStream = Stream.periodic(Duration(seconds: 1), (i) => i);

var myBeacon = Beacon.streamRaw(myStream,initialValue: 0);

myBeacon.subscribe((value) {
  print(value); // Outputs 0,1,2,3,...
});

Beacon.future: #

Creates a FutureBeacon that initializes its value based on a future. This can be refreshed by calling the reset method.

If manualStart is true, the future will not execute until [start()] is called.

var myBeacon = Beacon.future(() async {
  return await Future.delayed(Duration(seconds: 1), () => 'Hello');
});

myBeacon.subscribe((value) {
  print(value); // Outputs AsyncLoading immediately then AsyncData('Hello') after 1 second
});

FutureBeacon.overrideWith:

Replaces the current callback and resets the beacon by running the new callback. This can also be done with DerivedFutureBeacons.

var futureBeacon = Beacon.future(() async => 1);

await Future.delayed(k1ms);

expect(futureBeacon.value.unwrap(), 1);

futureBeacon.overrideWith(() async => throw Exception('error'));

await Future.delayed(k1ms);

expect(futureBeacon.value, isA<AsyncError>());

Beacon.list: #

The ListBeacon provides methods to add, remove, and update items in the list and notifies listeners without having to make a copy.

NB: The previousValue and current value will always be the same because the same list is being mutated. If you need access to the previousValue, use Beacon.writable

Beacon.hashSet:

Similar to Beacon.list(), but for Sets.

Beacon.hashMap:

Similar to Beacon.list(), but for Maps.

var nums = Beacon.list<int>([1, 2, 3]);

Beacon.effect(() {
 print(nums.value); // Outputs: [1, 2, 3]
});

nums.add(4); // Outputs: [1, 2, 3, 4]

nums.remove(2); // Outputs: [1, 3, 4]

AsyncValue: #

An AsyncValue is a wrapper around a value that can be in one of four states:idle, loading, data, or error. This is the value type of FutureBeacons,DerivedFutureBeacons and StreamBeacons.

var myBeacon = Beacon.future(() async {
  return await Future.delayed(Duration(seconds: 1), () => 'Hello');
});

print(myBeacon.value); // Outputs AsyncLoading immediately

await Future.delayed(Duration(seconds: 1));

print(myBeacon.value); // Outputs AsyncData('Hello')

AsyncValue.unwrap():

Casts this [AsyncValue] to [AsyncData] and return it's value. This will throw an error if the value is not an [AsyncData].

var name = AsyncData('Bob');
print(name.unwrap()); // Outputs: Bob

name = AsyncLoading();
print(name.unwrap()); // Throws error

AsyncValue.lastData:

Returns the latest valid data value or null. This is useful when you want to display the last valid value while loading new data.

var myBeacon = Beacon.future(() async {
  return await Future.delayed(Duration(seconds: 1), () => 'Hello');
});

print(myBeacon.value); // Outputs AsyncLoading immediately

print(myBeacon.value.lastData); // Outputs null as there is no valid data yet

await Future.delayed(Duration(seconds: 1));

print(myBeacon.value.lastData); // Outputs 'Hello'

myBeacon.reset();

print(myBeacon.value); // Outputs AsyncLoading

print(myBeacon.value.lastData); // Outputs 'Hello' as the last valid data when in loading state

Beacon.family: #

Creates and manages a family of related Beacons based on a single creation function.

This class provides a convenient way to handle related beacons that share the same creation logic but have different arguments.

Type Parameters: #

  • T: The type of the value emitted by the beacons in the family.
  • Arg: The type of the argument used to identify individual beacons within the family.
  • BeaconType: The type of the beacon in the family.

If cache is true, created beacons are cached. Default is false.

Example:

final apiClientFamily = Beacon.family(
 (String baseUrl) {
   return Beacon.readable(ApiClient(baseUrl));
 },
);

final githubApiClient = apiClientFamily('https://api.github.com');
final twitterApiClient = apiClientFamily('https://api.twitter.com');

Extensions: #

myWritable.wrap(anyBeacon): #

Wraps an existing beacon and consumes its values

Supply a (then) function to customize how the emitted values are processed.

var bufferBeacon = Beacon.bufferedCount<String>(10);
var count = Beacon.writable(5);

// Wrap the bufferBeacon with the readableBeacon and provide a custom transformation.
bufferBeacon.wrap(count, then: (value) {
  // Custom transformation: Convert the value to a string and add it to the buffer.
  bufferBeacon.add(value.toString());
});

print(bufferBeacon.buffer); // Outputs: ['5']
count.value = 10;
print(bufferBeacon.buffer); // Outputs: ['5', '10']

This method is available on all writable beacons, including BufferedBeacons; and can wrap any beacon since all beacons are readable.

mybeacon.next(): #

Listens for the next value emitted by this Beacon and returns it as a Future.

This method subscribes to this Beacon and waits for the next value that matches the optional [filter] function. If [filter] is provided and returns false for a emitted value, the method continues waiting for the next value that matches the filter. If no [filter] is provided, the method completes with the first value received.

If a value is not emitted within the specified [timeout] duration (default is 10 seconds), the method times out and returns the current value of the beacon.

final age = Beacon.writable(20);

Timer(Duration(seconds: 1), () => age.value = 21;);

final nextAge = await age.next(); // returns 21 after 1 second

mybeacon.buffer(): #

Returns a Beacon.bufferedCount that wraps this beacon.

NB: The returned beacon will be disposed when the wrapped beacon is disposed.

final age = Beacon.writable(20);

final bufferedAge = age.buffer(10);

bufferedAge.subscribe((value) {
  print(value); // Outputs: [20, 21, 22, 23, 24, 25, 26, 27, 28, 29]
});

for (var i = 0; i < 10; i++) {
  age.value++;
}

mybeacon.bufferTime(): #

Returns a Beacon.bufferedTime that wraps this beacon.

mybeacon.throttle(): #

Returns a Beacon.throttled that wraps this beacon.

mybeacon.filter(): #

Returns a Beacon.filtered that wraps this beacon.

mybeacon.debounce(): #

Returns a Beacon.debounced that wraps this beacon.

final query = Beacon.writable('');

const k500ms = Duration(milliseconds: 500);

final debouncedQuery = age
                      .filter((prev,next) => next.length > 3);
                      .debounce(duration: k500ms)

Pitfalls #

When using Beacon.derivedFuture, only beacons accessed before the async gap(await) will be tracked as dependencies.

final counter = Beacon.writable(0);
final doubledCounter = Beacon.derived(() => counter.value * 2);

final derivedFutureCounter = Beacon.derivedFuture(() async {
  // This will be tracked as a dependency because it's accessed before the async gap
  final count = counter.value;

  await Future.delayed(Duration(seconds: count));

  // This will NOT be tracked as a dependency because it's accessed after `await`
  final doubled = doubledCounter.value;

  return '$count x 2 =  $doubled';
});

When a derivedFuture depends on multiple future/stream beacons

  • DON'T:
final derivedFutureCounter = Beacon.derivedFuture(() async {
  // in this instance lastNameStreamBeacon will not be tracked as a dependency
  // because it's accessed after the async gap
  final firstName = await firstNameFutureBeacon.toFuture();
  final lastName = await lastNameStreamBeacon.toFuture();

  return 'Fullname is $firstName $lastName';
});
  • DO:
final derivedFutureCounter = Beacon.derivedFuture(() async {
  // acquire the futures before the async gap ie: don't use await
  final firstNameFuture = firstNameFutureBeacon.toFuture();
  final lastNameFuture = lastNameStreamBeacon.toFuture();

  // wait for the futures to complete
  final (String firstName, String lastName) = await (firstNameFuture, lastNameFuture).wait;

  return 'Fullname is $firstName $lastName';
});

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Metadata

A reactive primitive and simple state managerment solution for dart.

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Topics

#state #signal #reactive #beacon

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