Hands-On Design Patterns with Swift

Bastard Injection

Constructor overloads are fairly common in Swift codebases, but these could lead to the Bastard Injection anti-pattern. A common scenario is when we have a constructor that lets us inject a Test Double, but it also has a default parameter in the constructor:

class TodosService {    let repository: TodosRepository    init(repository: TodosRepository = SqlLiteTodosRepository()) {        self.repository = repository    }}

The biggest problem here is when the default implementation is a Foreign dependency, which is a class defined using another module; this creates a strong relationship between the two modules, making it impossible to reuse the class without including the dependent module too.

The reason someone is tempted to write a default ...