Jens Segers explains how to use PHP League's shiny new version of Container. The usage of ContainerInterface seems interesting:

League's container now implements the ContainerInterface, which is defined by the Container Interoperability group. This is really great as there are a few projects and frameworks which support this interface. For example, the Slim 3 micro framework already allows you to choose your own container flavour, as long as it implements the interface.

Read the full article at Jens' blog.

The League's Container seems like a nice alternative to PHP DI that I have been using.