Added Sensible Default ggrs::Config type GgrsConfig

[bushrat011899]

Objective

In the box_game example, there's a to-do related to ggrs::Config:

/// TODO: Find a way to hide the state type.

Solution

I've solved this to-do by creating a type GgrsConfig:

#[derive(Debug)]
pub struct GgrsConfig<Input, Address = SocketAddr, State = u8> {
    _phantom: PhantomData<(Input, Address, State)>,
}

impl<Input, Address, State> Config for GgrsConfig<Input, Address, State>
where
    Self: 'static,
    Input: Send + Sync + PartialEq + bytemuck::Pod,
    Address: Send + Sync + Debug + Hash + Eq + Clone,
    State: Send + Sync + Clone,
{
    type Input = Input;
    type State = State;
    type Address = Address;
}

Because GgrsConfig is a concrete type, it is allowed to have defaults for the type parameters Input, State, and Address required by ggrs::Config. As mentioned in the box_game example, u8 for State is already taken as a default (since State is unused in Bevy). I also took the liberty of setting Address to SocketAddr as I believe that is the most common type that will be used by end users. These defaults allow the example game to use:

pub type BoxConfig = GgrsConfig<BoxInput>;

I show a type definition here, as I suspect end users would prefer this option for the sake of brevity. Because this is all done through the addition of a simple zero-sized-type, all existing applications can continue using their custom Config types if they want, with no breaking changes.

[johanhelsing]

I like this. For the extreme_bevy tutorial, it means:

-struct GgrsConfig;
-
-impl ggrs::Config for GgrsConfig {
-    // 4-directions + fire fits easily in a single byte
-    type Input = u8;
-    type State = u8;
-    // Matchbox' WebRtcSocket addresses are called `PeerId`s
-    type Address = PeerId;
-}
+type ExtremeConfig = GgrsConfig<u8, PeerId>;

[gschup]

This is great syntactic sugar :)