Injektion

Introduction

A simple way to handle dependency injection using property wrappers. It is available as a Swift Package or as a CocoaPod. The concept is heavily based on the work of Antoine van der Lee:

https://www.avanderlee.com/swift/dependency-injection/

Install

Swift Package

Injektion can be added to an Xcode project as a swift package. Using the regular Xcode tool, search for the following URL:

https://github.com/andrewmcgee/Injektion

Cocoapods

Injektion can be added to a project as a pod by adding the folloing to your Podfile under the correct target:

pod 'Injektion', '~> 1.0.0'

and then running the following command in yout terminal:

pod install

Usage

To set up a dependency, define a new (optionally private) key struct that conforms to the DependencyKey protocol. Its current value should be the dependency, which can be abstracted behind a protocol.

private struct SomeDependencyKey: DependencyKey {
    static var currentValue: DependencyType = Dependency()
}

Then extend the Dependencies type to include a new key provider computed property. Its type should be the same as the DependencyKey's currentValue. Using its getter and setter it should act as a proxy for the static subscript of Dependencies that takes the implementation of DependencyKey's type defined above as an input.

extension Dependencies {
    
    var dependencyKeyProvider: DependencyType {
        get { Self[SomeDependencyKey.self] }
        set { Self[SomeDependencyKey.self] = newValue }
    }
}

With these parts in place, you can now refer to the dependency throughout you code in the following way:

class SomeClass {
    
    @Dependency(\.dependencyKeyProvider) private var dependency: DependencyType
    
}

You can update a dependency in two ways. Either like this:

class SomeClass {
    
    @Dependency(\.dependencyKeyProvider) private var dependency: DependencyType
    
    func updateDependency() {
        self.dependency = NewDependency()
    }
}

or directly like this:

Dependencies[SomeDependencyKey.self] = NewDependency()

Please note that if you update a dependency, then it will be updated in all the places where it is used.