SwinjectAutoregistration

SwinjectAutoregistration is an extension of Swinject that allows to automatically register your services and greatly reduce the amount of boilerplate code.

Requirements

• iOS 8.0+ / Mac OS X 10.10+ / tvOS 9.0+
• Xcode 8+

Installation

Swinject is available through Carthage or CocoaPods.

Carthage

To install Swinject with Carthage, add the following line to your Cartfile.

github "Swinject/Swinject" "2.7.0"
github "Swinject/SwinjectAutoregistration" "2.7.0"

Then run carthage update --no-use-binaries command or just carthage update. For details of the installation and usage of Carthage, visit its project page.

CocoaPods

To install Swinject with CocoaPods, add the following lines to your Podfile.

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0' # or platform :osx, '10.10' if your target is OS X.
use_frameworks!

pod 'Swinject', '2.7.0'
pod 'SwinjectAutoregistration', '2.7.0'

Then run pod install command. For details of the installation and usage of CocoaPods, visit its official website.

Registration

Here is a simple example to auto-register a pet owner

let container = Container()
container.register(Animal.self) { _ in Cat(name: "Mimi") } // Regular register method
container.autoregister(Person.self, initializer: PetOwner.init) // Autoregistration

where PetOwner looks like this:

class PetOwner: Person {
    let pet: Animal

    init(pet: Animal) {
        self.pet = pet
    }
}

The autoregister function is given the PetOwner initializer init(pet:Animal). From its signature Swinject knows that it needs a dependency Animal and resolves it from the container. Nothing else is needed.

Autoregistration becomes especially useful when used to register services with many dependencies. Compare autoregistration code:

container.autoregister(MyService.self, initializer: MyService.init)

with equivalent code in pure Swinject:

container.register(MyService.self) { r in 
	MyService(dependencyA: r.resolve(DependencyA.self)!, dependencyB: r.resolve(DependencyB.self)!, dependencyC: r.resolve(DependencyC.self)!, dependencyD: r.resolve(DependencyD.self)!)
}

Another advantage is that if you add more dependencies during the development the registration code doesn't have to be rewritten.

Registration with name

Service can be also given name - same as with the regular register method.

container.autoregister(Person.self, name: "johnny", initializer: PetOwner.init)

Arguments

You can also use auto-registration for services with dynamic arguments. Pet owner whose name needs to be passed as argument is defined like this:

class PetOwner: Person {
    let name: String
    let pet: Animal

    init(name: String, pet: Animal) {
        self.name = name
        self.pet = pet
    }
}

And registered like this

container.autoregister(Person.self, argument: String.self, initializer: PetOwner.init)

Swinject will register Person with the argument of type String. When container.resolve(Person.self, argument: "Michael") is called Swinject won't try to resolve String as dependency but instead pass "Michael" as the name.

To also pass pet as argument you can call

container.autoregister(Person.self, arguments: String.self, Animal.self, initializer: PetOwner.init)
//or
container.autoregister(Person.self, arguments: Animal.self, String.self, initializer: PetOwner.init)

The order of the arguments listed is interchangeable. The auto-registration can't be used with more arguments and/or dependencies of the same type.

What kind of sorcery is this?

Wondering how does that work? Generics are heavily leveraged for the auto-registration. For registering service with two dependencies something similar to a following function is used:

public func autoregister<Service, A, B>(_ service: Service.Type, initializer: (A, B) -> Service) -> ServiceEntry<Service> {
   return self.register(service.self, factory: { r in 
       return initializer(r.resolve(A.self)!, r.resolve(B.self)!)
   } as (ResolverType) -> Service)
}

The initializer is a function like any other. By passing it as a parameter its dependencies can be inferred as (A, B) and automatically resolved. These functions are generated for up to 20 dependencies. Checkout the code for more info.

Operators

This extension also aims to reduce the amount of boilerplate while improving readability of the registration code. For that reason the operator ~> is introduced.

Petowner(pet: r~>)

// equivalent to

Petowner(pet: r.resolve(Animal.self)!)

The dependency is again inferred from the type in the initializer. To specify a concrete class you can use:

Petowner(pet: r ~> Cat.self)

To use a named service:

Petowner(pet: r ~> (Cat.self, name: "mimi"))

or to pass argument/s:

Petowner(pet: r ~> (Cat.self, argument: "Mimi"))
Petowner(pet: r ~> (Cat.self, arguments: ("Mimi", UIColor.black)))

Limitations

When a service has multiple initializers, swift compiler can't be sure which should be used and you will get a ambigious use of init(x: y: z:). This can also happen if the service is extending another class that have initializer with the same number of arguments.

The solution is to specify the initializer like this:

container.autoregister(Person.self, initializer: PetOwner.init(name:pet:))

Auto-registration can't be used with named dependencies in their initializers. There is no way to get a name of dependency from the initializer. For example, following code can't be auto-registered:

container.register(Animal.self, name: "mimi") { _ in Cat(name: "Mimi") }
container.register(Animal.self, name: "charles") { _ in Cat(name: "Charles") }
container.register(Person.self) {
    PetOwner(pet: r.resolve(Animal.self, name: "mimi")
}

Swift 5.3

Since Swift 5.3 the compiler behaves differently when infering initializers in structs that have variables with a default value:

struct Cat {
    let height: Int = 50
}

Compiler will generate two init functions:

Cat.init and Cat.init(height:)

Since the Swift 5.3 the following registration

container.autoregister(Animal.self, initializer: Cat.init)

will try to use the Cat.init(height:) which will then fail with Unresolved service: Int Initializer: (Int) -> Animal

Solution is to make the compiler use the init without a parameter

container.autoregister(Animal.self, initializer: Cat.init as () -> Cat)

Credits

SwinjectAutoregistration generics is inspired by:

• Curry - Thoughtbot

License

MIT license. See the LICENSE file for details.