Dynamic - Supervision with "Fake" Polymorphism

This is just a simple attempt to create dynamically supervised children which can be called in a "fake" polymorphic way. There might be much better ways to do this, so if there is, let me know!

For this example, the idea is that different types of children could be supervised together, then called polymorphically, without knowing anything about the actual child.

To do this, a child is started through the supervisor. When the child initializes, it registers itself and its __MODULE__ within the Registry. After it's started, it can be invoked through a proxy, by the same supervisor that started it. If, however, a child doesn't implement the defined behaviour, it won't be started by the supervisor.

Installation

$ mix deps.get
$ mix deps.compile

Run It

Once you've got all the dependencies pulled, start it up within iex so you can start some child processes

iex -S mix run

Now that you're within iex, you can start some children. Try the following

iex(1)> Dynamic.Multi.Supervisor.start_child(Dynamic.Multi.One, "phil", "This is state")
{:ok, #PID<0.175.0>}
iex(2)> Dynamic.Multi.Supervisor.start_child(Dynamic.Multi.Two, "amy", "This is state too")
{:ok, #PID<0.178.0>}
iex(3)> Dynamic.Multi.Supervisor.start_child(Dynamic.Multi.Nope, "ooops", "This fails")
{:error, "Module 'Elixir.Dynamic.Multi.Nope' doesn't implement 'Dynamic.Multi' behaviour"}
iex(4)> Dynamic.Multi.Supervisor.toast("phil")
"ONE: This is state"
:ok
iex(5)> Dynamic.Multi.Supervisor.toast("amy")
"TWO: This is state too"
:ok

That's about it. You're starting two children of different types. When you call toast/1 with the child's name, it invokes the proxy within the supervisor. The proxy then looks up the child within the Registry and calls the child's toast/1 function. Done!