this.swift

protocol Injectable {
    init()
}

class MyDependency {}

class MyClass: Injectable {
    private let dep: MyDependency

    required convenience init() {
        self.init(dep: MyDependency())
    }

    init(dep: MyDependency) {
        self.dep = dep
    }
}

class MyClass2: MyClass {
    private let dep2: MyDependency

    required convenience init() {
        self.init(dep: MyDependency(), dep2: MyDependency())
    }

    init(dep: MyDependency, dep2: MyDependency) {
        self.dep2 = dep2

        super.init(dep: dep)
    }
}