Swift 2 has introduced Protocol Extensions, which reinforces Protocol Oriented Programming and usage of value types. Swinject can handle not only a reference type but also a value type as a component created by a factory.
Here you have Turtle struct implementing AnimalType protocol.
protocol AnimalType {
var name: String { get set }
}
struct Turtle: AnimalType {
var name: String
}
The struct instance can be registered and resolved as below.
let container = Container()
container.register(AnimalType.self) { _ in Turtle(name: "Ninja") }
var turtle1 = container.resolve(AnimalType.self)!
print(turtle1.name) // prints "Ninja"
Because turtle1 is actually a struct instance although its type is inferred as protocol AnimalType there, assigning it to a new parameter creates a new instance.
var turtle2 = turtle1
turtle2.name = "Samurai"
print(turtle2.name) // prints "Samurai"
print(turtle1.name) // prints "Ninja"
In Swinject or other DI frameworks, a service type can be not only a protocol but also a concrete or abstract classes. A special case is that the service type and component type are identical. The case is called Self-registration or Self-binding. Here is an example of self-binding with Swinject.
let container = Container()
container.register(AnimalType.self) { _ in Cat(name: "Mimi") }
container.register(PetOwner.self) { r in
PetOwner(name: "Selfie", pet: r.resolve(AnimalType.self)!)
}
Then a PetOnwer service is resolved as itself.
let owner = container.resolve(PetOwner.self)!
print(owner.name) // prints "Selfie"
print(owner.pet.name) // prints "Mimi"
Where the protocols and classes are:
protocol AnimalType {
var name: String { get set }
}
class Cat: AnimalType {
var name: String
init(name: String) {
self.name = name
}
}
class PetOwner {
let name: String
let pet: AnimalType
init(name: String, pet: AnimalType) {
self.name = name
self.pet = pet
}
}