Flywheel

A simple and predictable state management library inspired by Flux + Elm + Redux. Flywheel is built on top of Corotuines using the concepts of structured concurrency. At the core, lies the State Machine which is based on actor model.

Why Flywheel?

The goal was to make the state management concept of Redux simple, understandable & easy to use in Kotlin based projects. To achieve that, we adapted only the core concepts from Redux and slightly modified them. We excluded Android, Apple or any platform-specific dependencies. It is just pure Kotlin. By doing so, you are free to choose your architecture that best suits your codebase, no need to make any big refactor to fit in Flywheel. Don't be fooled by its simplicity, Flywheel got you covered for all practical use-cases. Even if we missed anything, it can be easily extended to support your use cases.

Getting started

In Kotlin Multiplatfrom project:

kotlin {
  sourceSets {
      val commonMain by getting {
          dependencies {
              implementation("com.msabhi:flywheel:1.3.0")
          }
      }
  }
}

In Android / Gradle project:

dependencies {

    implementation("com.msabhi:flywheel-android:1.3.0")
}

In Apple platforms (Swift Package Manager)

In Xcode, go to File → Add Package Dependencies and enter the repository URL:

https://github.com/abhimuktheeswarar/Flywheel.git

Or add it to your Package.swift:

// swift-tools-version:5.9
import PackageDescription

let package = Package(
    name: "YOUR_PROJECT_NAME",
    dependencies: [
        .package(url: "https://github.com/abhimuktheeswarar/Flywheel.git", from: "1.3.0"),
    ]
)

Each GitHub release includes a Flywheel.xcframework.zip artifact with a matching Package.swift manifest containing the URL and checksum.

Building the XCFramework locally

The XCFramework is not checked into the repository. To build it from source:

# Build and copy into flywheel/xcframework/ for local SPM use
./gradlew :flywheel:copyXCFrameworkToRepo

# Build, zip and generate a release-ready Package.swift with checksum
./gradlew :flywheel:generatePackageSwift

# Full release prep: build XCFramework, generate Package.swift, copy to repo root
./gradlew prepareSpmRelease

Usage

This is how a simple counter example looks like.

1. Define a state.

   data class CounterState(val counter: Int = 0) : State

2. Define actions that can change the state.

   sealed interface CounterAction : Action {
   
       object IncrementAction : CounterAction
   
       object DecrementAction : CounterAction
   }

3. Define a reducer that updates the state based on the action & current state.

   val reduce = reducerForAction<CounterAction, CounterState> { action, state ->
       with(state) {
           when (action) {
               is CounterAction.IncrementAction -> copy(counter = counter + 1)
               is CounterAction.DecrementAction -> copy(counter = counter - 1)
           }
       }
   }

4. Create a StateReserve.

   val stateReserve = StateReserve(
       config = getDefaultStateReserveConfig(),
       initialState = InitialState.set(CounterState()),
       reduce = reduce,
       middlewares = null)

5. Listen for state changes

   stateReserve.states.collect { state -> println(state.counter) }

6. Send actions to StateReserve to update the state.

   stateReserve.dispatch(IncrementAction)

7. To update the state based on its current value (e.g. from concurrent SideEffects), dispatch a ReduceAction — an action that carries a delta and its own merge. Its reduce is applied atomically against the current state on the state machine, so concurrent updates compose instead of overwriting each other. Do the heavy computation first, then dispatch only the precomputed delta.

   data class AddToCountAction(val amount: Int) : ReduceAction<CounterState> {
       override fun reduce(state: CounterState) = state.copy(counter = state.counter + amount)
   }
   
   stateReserve.dispatch(AddToCountAction(5))

To learn more about Flywheel, head on over to our wiki.

License

Copyright (C) 2021 Abhi Muktheeswarar

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.