swarm/src/lib: Remove Deref and DerefMut impls on Swarm

[mxinden]

Remove Deref and DerefMut implementations previously dereferencing
to the NetworkBehaviour on Swarm. Instead one can access the
NetworkBehaviour via Swarm::behaviour and Swarm::behaviour_mut.
Methods on Swarm can now be accessed directly, e.g. via
my_swarm.local_peer_id().

Reasoning: Accessing the NetworkBehaviour of a Swarm through Deref
and DerefMut instead of a method call is an unnecessary complication,
especially for newcomers. In addition, Swarm is not a smart-pointer
and should thus not make use of Deref and DerefMut, see documentation
from the standard library below.

Deref should only be implemented for smart pointers to avoid
confusion.

https://doc.rust-lang.org/std/ops/trait.Deref.html

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For the reasons mentioned above I would consider this breaking change worth doing. This has been shortly discussed in #1073 in the past. What do people think?

[thomaseizinger]

FWIW, I am in favor of this change. I always found Swarm::dial_addr hard to use because I know that it was there and it always takes me a while to remember that I have to call it as an associated function.

[romanb]

No objections from my side.

[mxinden]

I would deem 5 days enough as a review period, thus merging now. Thanks for the reviews. Happy for future comments / suggestions.

[dvc94ch]

Sorry I didn't see this sooner and comment. But I wonder if #2006 isn't the better approach. Keep the deref/deref_mut and instead removing the swarm methods/events in favor of more inject_*event* on NetworkBehaviour and more NetworkBehaviourActions. One wart of libp2p is having multiple ways of doing things. Users can register some channels or something if they really need to handle events outside of the swarm.

[thomaseizinger]

@dvc94ch In my understanding, that is a orthogonal issue.

With this patch, we simply force users to explicitely type swarm.behaviour.foobar instead of just swarm.foobar. That is slightly more verbose but also more idiomatic Rust because Deref is only meant for smart-pointers.

As a result, we were able to remove the unintuitve associated functions for calling others things on Swarm like local_peer_id etc

Improving the NetworkBehaviour and all the things we talked about in the other thread are still possible as far as I can see :)

[dvc94ch]

I think there are other cases where using Deref is valid, for example when creating a new type wrapper to implement a foreign trait on a foreign type.

But yes, I think it's orthogonal, I was just worried about too many api changes for users.

[MOZGIII]

What do people think?

Thx so much for doing this!