Dertisch

A swifty MVP framework for Swift apps

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Preamble

Some of the following is out-of-date and is awaiting updates.

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Dertisch is a lightweight Swift framework built around dependency injection. Part MVVM and part VIPER, its hybrid nature makes it strictly neither, but instead an MVP framework specifically designed to be swifty via the protocol oriented nature of Swift. The framework's name forms a culinary analogical acronym designed to explain its own hybrid nature.

• D The Maître D
• E Entrées
• R Restaurant Staff
• T Tables
• I Ingredients
• S Sous Chefs
• C Customers
• H Head Chefs

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The Restaurant as a Design Pattern

Most design patterns are simple design patterns in that they translate their own purposes well without regard of how they relate to other patterns in a given app. When put together - a factory, some observers, and a decorator, say - it sounds like the character list from an episode of Monty Python: there is no common element tying these metaphors together. Writers describe this situation as mixed metaphors: the literary equivalent of an anti-pattern or bad code smell. Dertisch alleviates this bad smell by implementing a complex design pattern: the metaphors make sense in isolation but also collectively. And a good restaurant has a very similar structure to a good app:

• Most restaurants are variations on a salle/kitchen theme, and most app architectures are variations on a view/model theme.
• La salle of a good restaurant is visually enticing, warm and comfortable, and on brand for its particular cuisine. Good app views are likewise.
• The kitchen of a good restaurant is clean, efficient, well organized, and focused on the preparation of raw ingredients. Good app models are likewise.
• A good restaurant maintains a clear division between its salle and its kitchen, with the waiting staff connecting the two. Good apps are likewise.

A complex design pattern like this allows us to see the steps in a given procedure as if they were plot developments in a movie, which makes them: 1. easier to grasp; and 2. easier to conceptualize holistically.

To quote the team behind RxSwift:

People are creatures with huge visual cortexes. When we can visualize a concept easily, it's a lot easier to reason about.

For instance, instead of:

user interaction ->
event fired ->
data fetched ->
data parsed ->
view updates;

we have:

customer makes order ->
waiter takes order ->
ingredients sourced ->
chefs prepare food ->
table laid with dishes.

Dertisch's restaurant design pattern is compromized of multiple simple design patterns divided into three categories:

• customer patterns: customers, and restaurant tables;
• kitchen patterns: head chefs, sous chefs, and ingredients; and
• salle patterns: waiters, the maitre d, and the sommelier.

La salle is a French noun meaning "the dining room in a restaurant" in this context.

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How Dertisch is "swifty"

The swiftiness of Dertisch comes via its many hats philosophy, in which objects have different functions and properties exposed depending on the given context.

There is a chain of responsibility passing from Customer to Ingredient and back again through a series of hands that all have one specific role.

• Ingredients are data;
• Sous chefs parse data;
• Head chefs combine data;
• Waiters present data; and
• Customers consume data.

Theoretically, two overlapping objects - a Waiter and its HeadChef say - have delegate-like access to each other in that they only have access a limited subset of each other's functionality. To take an example, the responsibilities of a HeadChef are:

• to accept orders from waiters;
• to assign tasks to sous chefs;
• to prepare dishes from the prep of sous chefs; and
• to give waiters dishes for customers.

In a real restaurant a Waiter would only be able to get its HeadChef to undertake the first of these responsibilities, and conversely the HeadChef would only be able to get its Waiter to undertake the last. However, if a Waiter had actual delegate access to its HeadChef it could potentially access the other two responsibilities by casting its HeadChef as a HeadChefForSousChef. To guard against this, HeadChefs are not instances of classes which implement HeadChefForSousChef and HeadChefForWaiter protocols, but instead instances of classes that contain discrete concrete instances of classes that implement HeadChefForSousChef and HeadChefForWaiter protocols

HeadChef is a part-public, part-internal class that has its own HeadChefForWaiter and HeadChefForSousChef objects, which themselves are defined as protocols that must be implemented concretely as specific classes. These specific classes are referred to as Facets, as in facets of a personality (and also in reference to the Facade design pattern).

public protocol HeadChefFacet: class {
	init(_ headChef: HeadChef, _ key: String)
}

public protocol HeadChefForWaiter: HeadChefFacet {
	func give(_ order: CustomerOrder, _ key: String)
}

public protocol HeadChefForSousChef: HeadChefFacet {
	func give(_ prep: InternalOrder)
}

public protocol HeadChefProtocol {
	func forWaiter(_ key: String) -> HeadChefForWaiter?
	func forSousChef(_ key: String) -> HeadChefForSousChef?
	func waiter(_ key: String) -> WaiterForHeadChef?
}

internal protocol HeadChefInternalProtocol: ComplexColleagueProtocol, StaffMember {
	init(
		_ key: String,
		_ forWaiterType: HeadChefForWaiter.Type?,
		_ forSousChefType: HeadChefForSousChef.Type?,
		_ resources: [String: KitchenResource]?)
	func inject(_ waiter: WaiterForHeadChef?)
}

public class HeadChef: HeadChefInternalProtocol {
	...
}

extension HeadChef: HeadChefProtocol {
	...
}

A HeadChef's internal functionality is entirely concerned with dependency injection, whilst its public functionality is entirely concerned with granting access to its other facets. Keys are passed around internally in order to ensure that only facets of, say, a HeadChef can access both: its other facets; and also facets in its overlapping objects, in this case the WaiterForHeadChef object of a Waiter instance.

class SomeHeadChefForWaiter: HeadChefForWaiter {
	private let headChef: HeadChef
	private let key: String

	required init(_ headChef: HeadChef, _ key: String) {
		self.headChef = headChef
		self.key = key
	}

	func give(_ order: CustomerOrder, _ key: String) {
		headChef.waiter(key)?.serve(main: FulfilledOrder("dishCooked"))
	}
}

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The Roles in Dertisch

D is for The Maître D

The head waiter. The Maître D is classically a VIPER routing, which controls the addition and removal of views and manages relationships between customers, waiters, and head chefs.

E is for Entrées

The dishes customers start with. Entrées initialise viewControllers with data and are classically VIPER entities, which are simple data objects.

R is for Restaurant Staff

The waiting staff. Waiters are classically part VIPER presenters and part MVVM viewModels - ergo MVP presenters - which are given data by head chefs in order to populate and control views, whilst the Sommelier (the wine waiter) is classically a proxy which specifically provides multilingual support for text.

T is for Tables

The physical tables at which customers are seated. Restaurant Tables are classically viewControllers, the screens the user sees.

I is for Ingredients

The raw materials of any dish. Ingredients are classically services, which query APIs etc. for data.

S is for Sous Chefs

The second-in-command chefs who take the ingredients and combine them into dishes. Sous Chefs are classically proxies, which get and set data internally.

C is for Customers

The people ordering the food. Customers are classically users.

H is for Head Chefs

The people who control the kitchen staff and the dishes. Head Chefs are classically VIPER interactors, which have access to specific sous chefs in order to create particular combinations of data.

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An example interaction in Dertisch

• A customer gives an order to the waiter, who takes it to the kitchen (a user interacts with a view, sending a request to its presenter, which in turn passes the request to its interactor);
• the head chef instructs their staff as to the required dishes (the interactor queries its proxies);
• the staff cook ingredients and present the head chef with the dishes (the proxies combine data they already have with data they need, probably asynchronously, from their services);
• the head chef gives the dishes to the waiter, who approaches the customer (the interactor calls its presenter with data, which it stores before informing the view that there is new data available);
• the waiter and the sommelier serve the customer (the view populates itself via its presenter and its textProxy); and
• the table is laid with dishes (the view updates in accordance with the original interaction of the user).

Dertisch is designed to provide the functionality common to most apps, which specifically (at present) means the following.

On the Model side:

• API calls;
• management of external images;
• simplified access to Core Data;
• simple data storage for runtime properties;
• simplified integration of bundled json files; and
• the capacity to add bespoke proxies and services.

And on the View side:

• registration and presentation of Customers with related Waiters and Head Chefs; and
• multi-language text support.

Head Chefs work by implementing the HeadChef protocol; waiters by implementing the Waiter protocol; and customers by subclassing Customer.

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Using Dertisch

Dertisch allows you to create bespoke sous chefs and ingredients tailored towards your app's specific needs, and also comes with four in-built ingredients classes, and two in-built salle classes serving functionality common to all apps:

KITCHEN: INGREDIENTS

FoodDelivery
// provides access to RESTful APIs

Freezer
// provides simplified access to Core Data storage

Images
// provides capacity to load and get copies of images

Larder
// provides simplified access to json bundled with the app

SALLE

MaitreD
// manages the addition and removal of Customers and their relationships with Head Chefs and Waiters

Sommelier
// provides multi-language support for screen text

The built-in kitchen ingredients are very lightweight. For instance, FoodDelivery has a single call(_:from:method:flagged:) function that uses URLSession.shared.dataTask(with:). Should you need more from your API service, you can simply create your own, say, AlamofireIngredient and put all the bells and whistles into it that you need.

All kitchen classes in Dertisch are injected as singleton-with-a-small-s single instances. For instance, this mean that two separate Head Chefs that both have an instance of Images injected have the same instance of Images injected, so any properties set on that instance by one Head Chef will be readable by the other, and vice versa. And the same goes for all subsequent injections of Images elsewhere.

MaitreD is responsible for starting Dertisch apps; Sommelier is a mandatory requirement for all Dertisch view controllers; and Sommelier depends upon Larder, so these three are instantiated by default. The others are instantiated on a need-to-use basis.

Start your Dertisch app by calling MaitreD.greet(firstCustomer:) from AppDelegate:

class AppDelegate: UIResponder, UIApplicationDelegate {

	var window: UIWindow?

	func application(
		_ application: UIApplication,
		didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
		window = UIWindow(frame: UIScreen.main.bounds)
		MaitreD().greet(firstCustomer: "SomeCustomer", window: window!)
		return true
	}
}

MaitreD's start up routine includes a call to its own registerStaff(with key: String) function, which is where the app's required kitchen and restaurant staff must be registered. Extend MaitreD implementing MaitreDExtension to utilise this function:

extension MaitreD: MaitreDExtension {
	public func registerStaff(with key: String) {
//		register(Images.self, with: key, injecting: [FoodDelivery.self])
		register(SomeSousChef.self, with: key)
		register(SomeIngredient.self, with: key, injecting: [SomeSousChef.self])
		introduce(
			"SomeCustomer",
			as: SomeCustomer.self,
			with: key,
			waiter: SomeWaiter.self,
			chef: SomeHeadChef.self,
			kitchenStaff: [Images.self])
		introduce(
			"SomeOtherCustomer",
			 as: SomeOtherCustomer.self,
			 with: key)
	}
}

In the above example, because Images is commented out, injectable instances of this kitchen class will not be instantiated, as whatever app it is that is utilising this code presumably has no need of its functionality (it would make more sense to simply delete this line, but it is included here to demonstrate how they would be used if it was needed).

Dertisch kitchen classes can have other kitchen classes injected into them. For instance, in the code example above Images has FoodDelivery injected as it depends upon it to load external images.

In the first introduce(...) function above, SomeCustomer, SomeWaiter, and SomeHeadChef are bespoke classes written for the implementing app in question, and the registration function is which they appear creates a viewController -> presenter <- interactor relationship. kitchenStaff is an optional array in which one lists the sous chef classes that SomeHeadChef will need to do their job.

The second introduce(...) function above shows the example of a view controller that has no need of a waiter or a head chef, meaning this is a simple page with no dependence on data.

The above code example features the two model classes SomeSousChef and SomeIngredient. These are bespoke kitchen classes not included in Dertisch but written specifically for the implementing app in question. The boilerplate code for SomeSousChef looks like this:

class SomeSousChef {
	var headChef: HeadChefForKitchenMember?
	required init(_ resources: [String: KitchenResource]?) {}
}

extension SomeSousChef: KitchenResource {}

The boilerplate for SomeIngredient looks like this:

class SomeIngredient {
	required init(_ resources: [String: KitchenResource]?) {}
}

extension SomeIngredient: Ingredients {}

A boilerplate Customer looks like this:

class SomeCustomer {
	required init(maitreD: MaitreD, restaurantTable: RestaurantTable, waiter: WaiterForCustomer, sommelier: Sommelier?) {}
}

extension SomeCustomer: Customer {}

And a boilerplate Waiter looks like this:

class SomeWaiter: Waiter {
	required init(maitreD: MaitreD) {}
}

extension SomeWaiter: WaiterForMaitreD {
	func introduce(_ customer: CustomerForWaiter, and headChef: HeadChefForWaiter?) {}
}

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Indepth Documentation

There are more elements to Dertisch than those described above, including a host of optional functions that customer, waiters, sous chefs, etc can implement as and when needed. However, because nobody except myself is known to be using it presently I see no need for greater detail yet. If you would like to know more, please ask.

note to self - things to document:

• Project settings [main target] > General > Deployment Info > Main Interface [leave empty]

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Developmental Roadmap

Dertisch is still in beta and whilst no official timescale exists for development, suggestions are as follows:

• make Customer and Waiter RxSwift compatible;
• move optional KitchenMembers into their own repos to minimise the footprint of the core framework;
• warnings if instances of Waiter don't have requisite dependencies injected;
• rename Images ingredient;
• make classes, structs, and protocols that can be made internal and/or final just that;
• make utils functions native class extensions instead;
• change class etc. names into their design-pattern originals (Waiter to Presenter say) and then make restaurant-design-pattern wrappers for them (akin to RxSwift Traits);
• new MetricsSousChef for device-specific numeric constants;
• new FirebaseIngredient;
• instigate Redux-style 'reducer' process for kitchen classes so they can become structs that overwrite themselves;
• replace endShift() functions with weak vars etc?;
• force Freezer to take dataModelName at start up;
• reintroduce timeout stopwatch to FoodDelivery;
• complete list of MIME types in FoodDelivery;
• create example boilerplate app;
• remove fatal errors.

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On the names "Dertisch" and "JosephBeuysMum"

In 1984 the German painter Martin Kippenberger painted a portrait entitled "The Mother of Joseph Beuys". Beuys was also a German artist, working principally in sculpture and conceptual pieces, and was a contemporary of Kippenberger. The portrait does not capture the likeness of Beuys' mother, Frau Johanna Beuys. It does not even capture the likeness of a woman. It is said to be a self-portrait, but does not capture the likeness of Kippenberger especially well either. However, it does capture the likeness of someone called "Richard Willis" surprisingly well. Richard is the author of Dertisch, and was born the same year that the real Frau Johanna Beuys died. He is the person behind the various manifestations of the "JosephBeuysMum" username online, and the avatar he uses on these accounts is a cropped thumbnail of Kippenberger's painting.

"Dertisch" means "the table" in Deutsche, and is the name of an artwork by Joseph Beuys. Given that the framework is built around the metaphorical notion of serving dishes to restaurant customers, from all of Beuys' works Dertisch fits excellently as a name.

It also sounds a bit like "Dirtish", which is fun.