Rupert  Beatty

Rupert Beatty


Katana-swift: Swift Apps in A Swoosh!


Katana is a modern Swift framework for writing iOS applications' business logic that are testable and easy to reason about. Katana is strongly inspired by Redux.

In few words, the app state is entirely described by a single serializable data structure, and the only way to change the state is to dispatch a StateUpdater. A StateUpdater is an intent to transform the state, and contains all the information to do so. Because all the changes are centralized and are happening in a strict order, there are no subtle race conditions to watch out for.

We feel that Katana helped us a lot since we started using it in production. Our applications have been downloaded several millions of times and Katana really helped us scaling them quickly and efficiently. Bending Spoons's engineers leverage Katana capabilities to design, implement and test complex applications very quickly without any compromise to the final result.

We use a lot of open source projects ourselves and we wanted to give something back to the community, hoping you will find this useful and possibly contribute. ❤️

State of the project

We wrote several successful applications using the layer that Katana and Tempura provide. We still think that their approach is really a good one for medium-sized applications but, as our app grows, it becomes increasingly important to have a more modular architecture. For this reason, we have migrated our applications to use The Composable Architecture.


Your entire app State is defined in a single struct, all the relevant application information should be placed here.

struct CounterState: State {
  var counter: Int = 0

The app State can only be modified by a StateUpdater. A StateUpdater represents an event that leads to a change in the State of the app. You define the behaviour of the State Updater by implementing the updateState(:) method that changes the State based on the current app State and the StateUpdater itself. The updateState should be a pure function, which means that it only depends on the inputs (that is, the state and the state updater itself) and it doesn't have side effects, such as network interactions.

struct IncrementCounter: StateUpdater {
  func updateState(_ state: inout CounterState) {
    state.counter += 1

The Store contains and manages your entire app State. It is responsible of managing the dispatched items (e.g., the just mentioned State Updater).

// ignore AppDependencies for the time being, it will be explained later on
let store = Store<CounterState, AppDependencies>()

You can ask the Store to be notified about every change in the app State.

store.addListener() { oldState, newState in
  // the app state has changed

Side Effects

Updating the application's state using pure functions is nice and it has a lot of benefits. Applications have to deal with the external world though (e.g., API call, disk files management, …). For all this kind of operations, Katana provides the concept of side effects. Side effects can be used to interact with other parts of your applications and then dispatch new StateUpdaters to update your state. For more complex situations, you can also dispatch other side effects.

Side Effects are implemented on top of Hydra, and allow you to write your logic using promises. In order to leverage this functionality you have to adopt the SideEffect protocol

struct GenerateRandomNumberFromBackend: SideEffect {
  func sideEffect(_ context: SideEffectContext<CounterState, AppDependencies>) throws {
    // invokes the `getRandomNumber` method that returns a promise that is fullfilled
    // when the number is received. At that point we dispatch a State Updater
    // that updates the state
        .then { randomNumber in context.dispatch(SetCounter(newValue: randomNumber)) }

struct SetCounter: StateUpdater {
  let newValue: Int
  func updateState(_ state: inout CounterState) {
    state.counter = self.newValue

Moreover, you can leverage the Hydra.await operator to write logic that mimics the async/await pattern, which allows you to write async code in a sync manner.

struct GenerateRandomNumberFromBackend: SideEffect {
  func sideEffect(_ context: SideEffectContext<CounterState, AppDependencies>) throws {
    // invokes the `getRandomNumber` method that returns a promise that is fulfilled
    // when the number is received.
    let promise = context.dependencies.APIManager.getRandomNumber()
    // we use Hydra.await to wait for the promise to be fulfilled
    let randomNumber = try Hydra.await(promise)

    // then the state is updated using the proper state updater
    try Hydra.await(context.dispatch(SetCounter(newValue: randomNumber)))

In order to further improve the usability of side effects, there is also a version which can return a value. Note that both the state and dependencies types are erased, to allow for more freedom when using it in libraries, for example.

struct PurchaseProduct: ReturningSideEffect {
  let productID: ProductID

  func sideEffect(_ context: AnySideEffectContext) throws -> Result<PurchaseResult, PurchaseError> {

    // 0. Get the typed version of the context
    guard let context = context as? SideEffectContext<CounterState, AppDependencies> else {
      fatalError("Invalid context type")

    // 1. purchase the product via storekit
    let storekitResult = context.dependencies.monetization.purchase(self.productID)
    if case .failure(let error) = storekitResult {
      return .storekitRejected(error)

    // 2. get the receipt
    let receipt = context.dependencies.monetization.getReceipt()

    // 3. validate the receipt
    let validationResult = try Hydra.await(context.dispatch(Monetization.Validate(receipt)))

    // 4. map error
    return validationResult
      .map { .init(validation: $0) }
      .mapError { .validationRejected($0) }

Note that, if this is a prominent use case for the library/app, the step 0 can be encapsulated in a protocol like this:

protocol AppReturningSideEffect: ReturningSideEffect {
  func sideEffect(_ context: SideEffectContext<AppState, DependenciesContainer>) -> Void

extension AppReturningSideEffect {
  func sideEffect(_ context: AnySideEffectContext) throws -> Void {
    guard let context = context as? SideEffectContext<AppState, DependenciesContainer> else {
      fatalError("Invalid context type")


The side effect example leverages an APIManager method. The Side Effect can get the APIManager by using the dependencies parameter of the context. The dependencies container is the Katana way of doing dependency injection. We test our side effects, and because of this we need to get rid of singletons or other bad pratices that prevent us from writing tests. Creating a dependency container is very easy: just create a class that conforms to the SideEffectDependencyContainer protocol, make the store generic to it, and use it in the side effect.

final class AppDependencies: SideEffectDependencyContainer {
  required init(dispatch: @escaping PromisableStoreDispatch, getState: @escaping GetState) {
        // initialize your dependencies here


When defining a Store you can provide a list of interceptors that are triggered in the given order whenever an item is dispatched. An interceptor is like a catch-all system that can be used to implement functionalities such as logging or to dynamically change the behaviour of the store. An interceptor is invoked every time a dispatchable item is about to be handled.


Katana comes with a built-in DispatchableLogger interceptor that logs all the dispatchables, except the ones listed in the blacklist parameter.

let dispatchableLogger = DispatchableLogger.interceptor(blackList: [NotToLog.self])
let store = Store<CounterState>(interceptor: [dispatchableLogger])


Sometimes it is useful to listen for events that occur in the system and react to them. Katana provides the ObserverInterceptor that can be used to achieve this result.

In particular you instruct the interceptor to dispatch items when:

  • the store is initialized
  • the state changes in a particular way
  • a particular dispatchable item is managed by the store
  • a particular notification is sent to the default NotificationCenter
let observerInterceptor = ObserverInterceptor.observe([
    // list of dispatchable items dispatched when the store is initialized

let store = Store<CounterState>(interceptor: [observerInterceptor])

Note that when intercepting a side effect using an ObserverInterceptor, the return value of the dispatchable is not available to the interceptor itself.

What about the UI?

Katana is meant to give structure to the logic part of your app. When it comes to UI we propose two alternatives:

Tempura: an MVVC framework we built on top of Katana and that we happily use to develop the UI of all our apps at Bending Spoons. Tempura is a lightweight, UIKit-friendly library that allows you to keep the UI automatically in sync with the state of your app. This is our suggested choice.

Katana-UI: With this library, we aimed to port React to UIKit, it allows you to create your app using a declarative approach. The library was initially bundled together with Katana, we decided to split it as internally we don't use it anymore. In retrospect, we found that the impedance mismatch between the React-like approach and the imperative reality of UIKit was a no go for us.

Tempura Katana UI

Signpost Logger

Katana is automatically integrated with the Signpost API. This integration layer allows you to see in Instruments all the items that have been dispatched, how long they last, and useful pieces of information such as the parallelism degree. Moreover, you can analyse the cpu impact of the items you dispatch to furtherly optimise your application performances.

Bending Spoons Guidelines

In Bending Spoons, we are extensively using Katana. In these years, we've defined some best pratices that have helped us write more readable and easier to debug code. We've decided to open source them so that everyone can have a starting point when using Katana. You can find them here.

Migration from 2.x

We strongly suggest to upgrade to the new Katana. The new Katana, in fact, not only adds new very powerful capabilities to the library, but it has also been designed to be extremely compatible with the old logic. All the actions and middleware you wrote for Katana 2.x, will continue to work in the new Katana as well. The breaking changes are most of the time related to simple typing changes that are easily addressable.

If you prefer to continue with Katana 2.x, however, you can still access Katana 2.x in the dedicated branch.


In Katana, the concept of middleware has been replaced with the new concept of interceptor. You can still use your middleware by leveraging the middlewareToInterceptor method.

Swift Version

Certain versions of Katana only support certain versions of Swift. Depending on which version of Swift your project is using, you should use specific versions of Katana. Use this table in order to check which version of Katana you need.

Swift VersionKatana Version
Swift 5.0Katana >= 6.0
Swift 4.2Katana >= 2.0
Swift 4.1Katana < 2.0

Where to go from here

Give it a shot

pod try Katana


Make awesome applications using Katana together with Tempura

Check out the documentation


You can also add Katana to Dash using the proper docset.


Katana is available through CocoaPods and Swift Package Manager, you can also drop Katana.project into your Xcode project.


iOS 11.0+ / macOS 10.10+

Xcode 9.0+

Swift 5.0+

Swift Package Manager

Swift Package Manager is a tool for managing the distribution of Swift code. It’s integrated with the Swift build system to automate the process of downloading, compiling, and linking dependencies.

There are two ways to integrate Katana in your project using Swift Package Manager:

  • Adding it to your Package.swift
  • Adding it directly from Xcode under File -> Swift Packages -> Add Package dependency..

In both cases you only need to provide this URL:


CocoaPods is a dependency manager for Cocoa projects. You can install it with the following command:

$ sudo gem install cocoapods

To integrate Katana into your Xcode project using CocoaPods you need to create a Podfile.

For iOS platforms, this is the content

source ''
platform :ios, '9.0'

target 'MyApp' do
  pod 'Katana'

Now, you just need to run:

$ pod install

Get in touch

Special thanks


  • If you've found a bug, open an issue;
  • If you have a feature request, open an issue;
  • If you want to contribute, submit a pull request;
  • If you have an idea on how to improve the framework or how to spread the word, please get in touch;
  • If you want to try the framework for your project or to write a demo, please send us the link of the repo.


Katana is maintained by Bending Spoons. We create our own tech products, used and loved by millions all around the world. Interested? Check us out!

Download Details:

Author: BendingSpoons
Source Code: 
License: MIT license

#swift #redux #ios #katana 

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Carmen  Grimes

Carmen Grimes


How to start an electric scooter facility/fleet in a university campus/IT park

Are you leading an organization that has a large campus, e.g., a large university? You are probably thinking of introducing an electric scooter/bicycle fleet on the campus, and why wouldn’t you?

Introducing micro-mobility in your campus with the help of such a fleet would help the people on the campus significantly. People would save money since they don’t need to use a car for a short distance. Your campus will see a drastic reduction in congestion, moreover, its carbon footprint will reduce.

Micro-mobility is relatively new though and you would need help. You would need to select an appropriate fleet of vehicles. The people on your campus would need to find electric scooters or electric bikes for commuting, and you need to provide a solution for this.

To be more specific, you need a short-term electric bike rental app. With such an app, you will be able to easily offer micro-mobility to the people on the campus. We at Devathon have built Autorent exactly for this.

What does Autorent do and how can it help you? How does it enable you to introduce micro-mobility on your campus? We explain these in this article, however, we will touch upon a few basics first.

Micro-mobility: What it is


You are probably thinking about micro-mobility relatively recently, aren’t you? A few relevant insights about it could help you to better appreciate its importance.

Micro-mobility is a new trend in transportation, and it uses vehicles that are considerably smaller than cars. Electric scooters (e-scooters) and electric bikes (e-bikes) are the most popular forms of micro-mobility, however, there are also e-unicycles and e-skateboards.

You might have already seen e-scooters, which are kick scooters that come with a motor. Thanks to its motor, an e-scooter can achieve a speed of up to 20 km/h. On the other hand, e-bikes are popular in China and Japan, and they come with a motor, and you can reach a speed of 40 km/h.

You obviously can’t use these vehicles for very long commutes, however, what if you need to travel a short distance? Even if you have a reasonable public transport facility in the city, it might not cover the route you need to take. Take the example of a large university campus. Such a campus is often at a considerable distance from the central business district of the city where it’s located. While public transport facilities may serve the central business district, they wouldn’t serve this large campus. Currently, many people drive their cars even for short distances.

As you know, that brings its own set of challenges. Vehicular traffic adds significantly to pollution, moreover, finding a parking spot can be hard in crowded urban districts.

Well, you can reduce your carbon footprint if you use an electric car. However, electric cars are still new, and many countries are still building the necessary infrastructure for them. Your large campus might not have the necessary infrastructure for them either. Presently, electric cars don’t represent a viable option in most geographies.

As a result, you need to buy and maintain a car even if your commute is short. In addition to dealing with parking problems, you need to spend significantly on your car.

All of these factors have combined to make people sit up and think seriously about cars. Many people are now seriously considering whether a car is really the best option even if they have to commute only a short distance.

This is where micro-mobility enters the picture. When you commute a short distance regularly, e-scooters or e-bikes are viable options. You limit your carbon footprints and you cut costs!

Businesses have seen this shift in thinking, and e-scooter companies like Lime and Bird have entered this field in a big way. They let you rent e-scooters by the minute. On the other hand, start-ups like Jump and Lyft have entered the e-bike market.

Think of your campus now! The people there might need to travel short distances within the campus, and e-scooters can really help them.

How micro-mobility can benefit you


What advantages can you get from micro-mobility? Let’s take a deeper look into this question.

Micro-mobility can offer several advantages to the people on your campus, e.g.:

  • Affordability: Shared e-scooters are cheaper than other mass transportation options. Remember that the people on your campus will use them on a shared basis, and they will pay for their short commutes only. Well, depending on your operating model, you might even let them use shared e-scooters or e-bikes for free!
  • Convenience: Users don’t need to worry about finding parking spots for shared e-scooters since these are small. They can easily travel from point A to point B on your campus with the help of these e-scooters.
  • Environmentally sustainable: Shared e-scooters reduce the carbon footprint, moreover, they decongest the roads. Statistics from the pilot programs in cities like Portland and Denver showimpressive gains around this key aspect.
  • Safety: This one’s obvious, isn’t it? When people on your campus use small e-scooters or e-bikes instead of cars, the problem of overspeeding will disappear. you will see fewer accidents.

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Carmen  Grimes

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Best Electric Bikes and Scooters for Rental Business or Campus Facility

The electric scooter revolution has caught on super-fast taking many cities across the globe by storm. eScooters, a renovated version of old-school scooters now turned into electric vehicles are an environmentally friendly solution to current on-demand commute problems. They work on engines, like cars, enabling short traveling distances without hassle. The result is that these groundbreaking electric machines can now provide faster transport for less — cheaper than Uber and faster than Metro.

Since they are durable, fast, easy to operate and maintain, and are more convenient to park compared to four-wheelers, the eScooters trend has and continues to spike interest as a promising growth area. Several companies and universities are increasingly setting up shop to provide eScooter services realizing a would-be profitable business model and a ready customer base that is university students or residents in need of faster and cheap travel going about their business in school, town, and other surrounding areas.

Electric Scooters Trends and Statistics

In many countries including the U.S., Canada, Mexico, U.K., Germany, France, China, Japan, India, Brazil and Mexico and more, a growing number of eScooter users both locals and tourists can now be seen effortlessly passing lines of drivers stuck in the endless and unmoving traffic.

A recent report by McKinsey revealed that the E-Scooter industry will be worth― $200 billion to $300 billion in the United States, $100 billion to $150 billion in Europe, and $30 billion to $50 billion in China in 2030. The e-Scooter revenue model will also spike and is projected to rise by more than 20% amounting to approximately $5 billion.

And, with a necessity to move people away from high carbon prints, traffic and congestion issues brought about by car-centric transport systems in cities, more and more city planners are developing more bike/scooter lanes and adopting zero-emission plans. This is the force behind the booming electric scooter market and the numbers will only go higher and higher.

Companies that have taken advantage of the growing eScooter trend develop an appthat allows them to provide efficient eScooter services. Such an app enables them to be able to locate bike pick-up and drop points through fully integrated google maps.

List of Best Electric Bikes for Rental Business or Campus Facility 2020:

It’s clear that e scooters will increasingly become more common and the e-scooter business model will continue to grab the attention of manufacturers, investors, entrepreneurs. All this should go ahead with a quest to know what are some of the best electric bikes in the market especially for anyone who would want to get started in the electric bikes/scooters rental business.

We have done a comprehensive list of the best electric bikes! Each bike has been reviewed in depth and includes a full list of specs and a photo.

Billy eBike


To start us off is the Billy eBike, a powerful go-anywhere urban electric bike that’s specially designed to offer an exciting ride like no other whether you want to ride to the grocery store, cafe, work or school. The Billy eBike comes in 4 color options – Billy Blue, Polished aluminium, Artic white, and Stealth black.

Price: $2490

Available countries

Available in the USA, Europe, Asia, South Africa and Australia.This item ships from the USA. Buyers are therefore responsible for any taxes and/or customs duties incurred once it arrives in your country.


  • Control – Ride with confidence with our ultra-wide BMX bars and a hyper-responsive twist throttle.
  • Stealth- Ride like a ninja with our Gates carbon drive that’s as smooth as butter and maintenance-free.
  • Drive – Ride further with our high torque fat bike motor, giving a better climbing performance.
  • Accelerate – Ride quicker with our 20-inch lightweight cutout rims for improved acceleration.
  • Customize – Ride your own way with 5 levels of power control. Each level determines power and speed.
  • Flickable – Ride harder with our BMX /MotoX inspired geometry and lightweight aluminum package


  • Maximum speed: 20 mph (32 km/h)
  • Range per charge: 41 miles (66 km)
  • Maximum Power: 500W
  • Motor type: Fat Bike Motor: Bafang RM G060.500.DC
  • Load capacity: 300lbs (136kg)
  • Battery type: 13.6Ah Samsung lithium-ion,
  • Battery capacity: On/off-bike charging available
  • Weight: w/o batt. 48.5lbs (22kg), w/ batt. 54lbs (24.5kg)
  • Front Suspension: Fully adjustable air shock, preload/compression damping /lockout
  • Rear Suspension: spring, preload adjustment
  • Built-in GPS

Why Should You Buy This?

  • Riding fun and excitement
  • Better climbing ability and faster acceleration.
  • Ride with confidence
  • Billy folds for convenient storage and transportation.
  • Shorty levers connect to disc brakes ensuring you stop on a dime
  • belt drives are maintenance-free and clean (no oil or lubrication needed)

**Who Should Ride Billy? **

Both new and experienced riders

**Where to Buy? **Local distributors or ships from the USA.

Genze 200 series e-Bike


Featuring a sleek and lightweight aluminum frame design, the 200-Series ebike takes your riding experience to greater heights. Available in both black and white this ebike comes with a connected app, which allows you to plan activities, map distances and routes while also allowing connections with fellow riders.

Price: $2099.00

Available countries

The Genze 200 series e-Bike is available at GenZe retail locations across the U.S or online via website. Customers from outside the US can ship the product while incurring the relevant charges.


  • 2 Frame Options
  • 2 Sizes
  • Integrated/Removable Battery
  • Throttle and Pedal Assist Ride Modes
  • Integrated LCD Display
  • Connected App
  • 24 month warranty
  • GPS navigation
  • Bluetooth connectivity


  • Maximum speed: 20 mph with throttle
  • Range per charge: 15-18 miles w/ throttle and 30-50 miles w/ pedal assist
  • Charging time: 3.5 hours
  • Motor type: Brushless Rear Hub Motor
  • Gears: Microshift Thumb Shifter
  • Battery type: Removable Samsung 36V, 9.6AH Li-Ion battery pack
  • Battery capacity: 36V and 350 Wh
  • Weight: 46 pounds
  • Derailleur: 8-speed Shimano
  • Brakes: Dual classic
  • Wheels: 26 x 20 inches
  • Frame: 16, and 18 inches
  • Operating Mode: Analog mode 5 levels of Pedal Assist Thrott­le Mode

Norco from eBikestore


The Norco VLT S2 is a front suspension e-Bike with solid components alongside the reliable Bosch Performance Line Power systems that offer precise pedal assistance during any riding situation.

Price: $2,699.00

Available countries

This item is available via the various Norco bikes international distributors.


  • VLT aluminum frame- for stiffness and wheel security.
  • Bosch e-bike system – for their reliability and performance.
  • E-bike components – for added durability.
  • Hydraulic disc brakes – offer riders more stopping power for safety and control at higher speeds.
  • Practical design features – to add convenience and versatility.


  • Maximum speed: KMC X9 9spd
  • Motor type: Bosch Active Line
  • Gears: Shimano Altus RD-M2000, SGS, 9 Speed
  • Battery type: Power Pack 400
  • Battery capacity: 396Wh
  • Suspension: SR Suntour suspension fork
  • Frame: Norco VLT, Aluminum, 12x142mm TA Dropouts

Bodo EV


Manufactured by Bodo Vehicle Group Limited, the Bodo EV is specially designed for strong power and extraordinary long service to facilitate super amazing rides. The Bodo Vehicle Company is a striking top in electric vehicles brand field in China and across the globe. Their Bodo EV will no doubt provide your riders with high-level riding satisfaction owing to its high-quality design, strength, breaking stability and speed.

Price: $799

Available countries

This item ships from China with buyers bearing the shipping costs and other variables prior to delivery.


  • Reliable
  • Environment friendly
  • Comfortable riding
  • Fashionable
  • Economical
  • Durable – long service life
  • Braking stability
  • LED lighting technology


  • Maximum speed: 45km/h
  • Range per charge: 50km per person
  • Charging time: 8 hours
  • Maximum Power: 3000W
  • Motor type: Brushless DC Motor
  • Load capacity: 100kg
  • Battery type: Lead-acid battery
  • Battery capacity: 60V 20AH
  • Weight: w/o battery 47kg

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