So you can define a behaviour and implement it. For example, lets use payment provider.
If we know we will have multiple payment providers (ex: Stripe, Paypal, etc…), we might want a behaviour for payment providers. We can do this with a behaviour.
We can define the behaviour and say that every module that implements the MyApp.PaymentProvider behaviour needs to implement a credit/2 and debit/2 for example.
Now in our own Stripe module we can @behaviour MyApp.PaymentProvider and that is saying that we will need to implement the 2 callbacks we defined:
debit/2credit/2
Now we have a way to make sure we are able to switch between Paypal and Stripe because they follow the same contract. Both Paypal.credit/2 and Stripe.credit/2 should take the same args and return the same type/structure.
With Phoenix, they have optional callbacks, You can define your own or use the default. That is why you do not need to implement Phoenix.LiveComponent.update/2, but you can impl it if you want.
In your module, if you put one @impl over a function, I believe the compiler will complain. Because you iplemented it for another callback but not that specific one, so it thinks you made a possible mistake.
