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Developing modular apps on
iOS
NSPresenter Madrid - February 28th
@pepibumur
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About me
— Production Engineer at
Shopify.
— Building tools for mobile
developers.
— Born and raised in the
❤
Murcia.
— Suffering the
☔
in Berlin.
—
#
ppinera.es
—
$
@pepibumur
—
%
[email protected]
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What/why/how
should I modularize my app?
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What
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"Modularizing an app consists on
organising your app code and
resources in multiple modules"
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A module can be
— A library: If it doesn't have resources.
— A framework: If it has them.
— Static: If it's linked at compile time.
— Dynamic: If it's linked at startup time.
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Static linking - Compilation time
Dynamic linking - Startup time
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Dynamic modules need to be
copied into the product for
dylib to link them
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Static modules not properly
linked might lead to duplicated
symbols
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Carthage & CocoaPods are two
examples of tools that
modularise your dependencies
Carthage: Dynamic linking
CocoaPods: Static & dynamic linking
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Most of apps are usually built
and grown as monoliths
1 target with the app source
1 target with the tests
(And maybe some extensions)
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Why
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If you are a freelancer
You might want to reuse code
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If you have multiple products
!⌚#
You might want to reuse code
(e.g. Shopify has 5 iOS apps)
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If you want to write weakly
coupled components
You can leverage modules interfaces
(internal by default in Swift)
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If you want to speed up your
workflow
⏰
And spend less time waiting for the compiler
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The compile time is
proportional to the size of the
codebase
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But...
Apple is improving the Swi! compiler
The compiler builds incrementally (only clean builds
should take more time)
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— ⌘ + B (10 minutes)
— Change code + (⌘ + B) (4 Seconds)
— Change something + (⌘ + B) - (Error)
— ⌘ + K (I'm sure this helps)
— ⌘ + B (10 minutes)
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— 30 developers.
— 10 clean builds per day.
— 10 minutes per clean build.
1000 hours spent per month
6.25 engineers
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!
Fortunately, there's
something you can do to avoid
this
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How
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This is just one approach
That works in my experience
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Layers
Project
Downsides
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Before anyone asks...
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Yes, to avoid the hassle of
dealing with versioning or git
submodules, all the modules in
the same repository
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Microfeatures
github.com/pepibumur/microfeatures-guidelines
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App module
Navigation
App lifecycle events
Dependency injector
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// App
import Core
class Registry {
static let client = Client(url: "https://shopify.com")
static let analytics = Tracker(providers: [.firebase])
static let logger = Logger()
}
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import Product
import Home
// Module: App
class HomeCoordinator: HomeDelegate {
let navigationController: UINavigationController!
// HomeDelegate
func didSelectProduct(id: String) {
let vc = ProductFeature(id: id, client: Registry.client, analytics: Registry.analytics)
.viewController
navigationController.pushViewController(productViewController)
}
}
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Features modules
Can be product or service features
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import Core
// Module: Product
public class ProductFeature {
public init(id: String, client: Client, analytics: Analytics) {
// Initialization
}
// !! We just expose UIKit classes
public var viewController: UIViewController {
// Initialization & dependency injection
}
}
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import Core
// Module: BackgroundSync
public class BackgroundSyncer {
public init(client: Client, store: Store) { /* Init */ }
public func sync(completion: @escaping (Error?) -> Void)
}
// Module: App
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
func application(_ application: UIApplication,
performFetchWithCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
Registry.backgroundSyncer.sync { error in
// Notify completionHandler
}
}
}
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Shared components are
extracted into foundation
modules
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// Module: Core
public class Client: Clienting {}
public class Logger: Logging {}
public class Store: Storing {}
public class SecureStore: SecureStoring {}
// Module: CoreTesting
public class MockClient: Clienting {
public var executeCount: UInt!
public var executeRequest: URLRequest!
public var executeStub: (Any?, Error?)!
}
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import XCTest
import Core
import CoreTesting //
!
@testable import BackgroundSync
final class BackgroundSyncerTests: XCTestCase {
var client: MockClient!
Var store: MockStore!
var subject: BackgroundSyncer!
override func setUp() {
super.setUp()
client = MockClient()
store = MockStore()
subject = BackgroundSyncer(client: client, store: store)
}
}
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// Module: Testing
import XCTest
public extension XCTestCase {
public func XCTAssertTapa(_ tapa: Tapa,
identifier: String? = nil,
tolerance: CGFloat = 0,
file: StaticString = #file,
line: UInt = #line) {
// Asserts the quality of the tapa
}
}
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// Module: UI
public class Color {}
public class Font {}
public class CustomView {}
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Examples app
Allow developers to try out the features that they build
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1 Workspace
Multiple projects
(fewer git conflicts per project)
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There are not so cool features
that I didn't mention
(until now)
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From the monolith to modules
!
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1. Extract build se!ings into config files.
2. Extract foundation components/extensions.
3. Build new features in modules.
4. Gradually extract the existing features.
⚠
Extracting is not easy
⚠
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Maintaining more than one
Xcode project
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Tips to ease maintenance
1. Extract settings into .xcconfig files (a reusable single
source of truth).
2. Automate the generation of Xcode projects (e.g. using
XcodeGen).
3. Just Debug and Release configurations.
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Continuous integration
(Usually clean builds)
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Tips to speed up CI builds
1. Enable parallelize builds on your schemes.
2. Selective builds on CI.
Modules:
- name: Search
path: Search/Sources/**
build: xcodebuild -workspace Search.xcworkspace -scheme Search
dependencies:
- Core
- name: Core
path: Core/Sources/**
build: xcodebuild -workspace Core.xcworkspace -scheme Core
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Catalisis (coming soon)
— Command line tool.
— Generates workspaces and projects for the module
you are working on.
— Caches modules to save time on CI and locally.
— Offers an API to build/test modules.
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# Examples
catalisis generate-xcodeproj App
catalisis build Core
catalisis test Orders
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Conclusions
— Do it of you really need it.
— (reuse or decouple code, save time)
— More independent and productive teams.
— Apple is also improving things.
— It comes with some costs and lack of tooling (tools
are optimized for monoliths)
— A transition into modules is tough.
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Thanks!
Slides: h!ps://goo.gl/KAC1EJ
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