Dependency Injection Examples With Swift 4

In software engineering, dependency injection is a technique whereby one object supplies the dependencies of another object. A dependency is an object that can be used (a service). An injection is the passing of a dependency to a dependent object (a client) that would use it.

The service is made part of the client’s state.[1] Passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern. - Wikipedia.

TL;DR.

Initializer injection

protocol Serializer {
    func serialize(data: Any) -> Data?
}

class RequestSerializer: Serializer {
    func serialize(data: Any) -> Data? {
        return nil
    }
}

class DataManager {
    var serializer: Serializer?

    init(serializer: Serializer) {
        self.serializer = serializer
    }
}

let serializer = RequestSerializer()
// DI
let dataManager = DataManager(serializer: serializer)

Property injection

protocol Serializer {
    func serialize(data: Any) -> Data?
}

class RequestSerializer: Serializer {
    func serialize(data: Any) -> Data? {
        return nil
    }
}

class DataManager {
    var serializer: Serializer?
}

let dataManager = DataManager()

// DI
dataManager.serializer = RequestSerializer()

Method Injection

protocol Request {}
protocol Serializer {}

class DataManager {
    func serializeRequest(_ request: Request, with serializer: Serializer) -> Data? {
        return nil
    }
}