Generates actions and a reducer from a set of pure functions.

Install

To use built_reducer, you will need your typical build_runner/code-generator setup.
First, install build_runner and built_reducer by adding them to your pubspec.yaml file:

# pubspec.yaml
dependencies:
  reducer:

dev_dependencies:
  build_runner:
  built_reducer:

This install three packages:

• build_runner, the tool to run code-generators
• built_reducer, the code generator
• reducer, a package containing base types for built_reducer.

Usage

import 'package:meta/meta.dart';
import 'package:reducer/reducer.dart';

part 'counter.g.dart';

@immutable
class CounterState {
  final int count;
  const CounterState(this.count);
}

class CounterReducer extends Reducer<CounterState, CounterAction>
    with _CounterReducer {
  const CounterReducer();

  CounterState add(CounterState previousState, {@required int value}) {
    return CounterState(previousState.count + value);
  }

  CounterState reset(CounterState previousState) {
    return CounterState(0);
  }
}

From there, to generate the missing <Name>Action, _<Name>Reducer and the action classes, you have two possibilities:

• flutter pub run build_runner build, if your package depends on Flutter
• pub run build_runner build otherwise

Then use the reducer from the actions :

var state = CounterState(0);
const reducer = CounterReducer();
state = reducer(state, const CounterAddAction(value: 5));
state = reducer(state, const CounterResetAction());

Resulting file

You have a result in the example folder.

Why using a reducer instead of methods directly.

Since each call is represented with an instance, you have more possibilities :

• Reproducing a sequence of calls.
• Adding middlewares
• Serializing calls
• Redux