Chapter 6, Dependency Injection with Constructor Injection

1. What are the steps we used to adopt constructor injection?

1. We identified the dependency we wanted to extract and eventually inject.
2. We removed the creation of that dependency and promoted it to a member variable.
3. We then defined the abstraction of the dependency as a local interface and changed the member variable to use that instead of the real dependency.
4. We then added a constructor with the abstraction of the dependency as a parameter so that we could ensure the dependency was always available.

2. What is a guard clause and when would you use it?

We defined guard clauses as a piece of code the ensured the dependency was supplied (in other words, not nil). In some cases, we used them in our constructors so that we could be 100% sure the dependency was provided.

 

3. How does constructor injection affect the...