In my experience these type of abstractions end up bloated with too many concerns which adds maintenance overhead. It's a lot simpler to simply add a `HashMap<B

In my experience these type of abstractions end up bloated with too many concerns which adds maintenance overhead. It's a lot simpler to simply add a `HashMap<Book.title, Book>` and cover with tests, than use an abstraction. I want languages to do less magic, not more, since I read code more than I write it.