Rob Allen has a new post to his site today showing you how to access services in a Slim 3 application using container injection instead of the previous "getInstance" method.

One of the changes between Slim Framework 2 and 3 is that the application singleton has gone. [...] In general, you didn't need access to $app itself, but rather you wanted access to something that the app knows about, such as a database adapter, or the router for access to the urlFor method to create a URL to a route. With Slim 3, there is no getInstance() on App, so you need to inject the instances of whatever you need where ever you need them.

He shows you how to create a simple Slim dependency injection container (service locator?) and push two kinds of objects in for later reuse. He shows how to reference this container from inside of your routes in both the callable/closure and class contexts. He also includes an example of referencing the same container from inside middleware (again in both the closure and class contexts).