Some past self version of me is saying, every class and function should be explicit about their dependencies, so that they are easily testable. John0 would say, “If you have a service that talks to a database, the database client should be an explicit dependency specified in the constructor. This makes the code easily testable.”

There is another version of myself from 10 minutes ago arguing it’s foolish to be explicit about everything. He’d point to this piece of code he’s just looked at: