Event Bridge Pattern

[Pfeil]

This is about a pattern to make plugins (even internal ones) independent of other code, even in terms of imports.

https://github.com/Pfeil/bevy-design-patterns/tree/generic-events/patterns/event_bridge

Let's shortly define some properties / levels of independence of a plugin:

1. the initialization (add_plugins) can be omitted, and your code will still work without any other adjustments like removing imports.
2. the plugin can be fully removed, and your code will still work without any other adjustments like removing imports.

I was aiming for both properties. So far, it at least works in the example case. Not sure how it applies in practice. This is a really early idea.

Things which came to my mind, but I was not able to try yet:

• can it be applied to more than events? Like components or other types one would need to import?
• is a configuration resource an alternative, and in which cases?
• can we make a wrapper module which packs the boilerplate and the plugin module in order to further structure the imports in a hierarchical, useful way? (probably yes)
• I believe this is already useful if either the sender or the emitter implement the pattern, at least in one way. I did not try yet, though. We could add some examples, e.g., by using a src/bin folder.
• We have a clone in there, we can probably avoid it somehow.
• I'd like to test / see it in some greater context to see how it works in practice.

[MiniaczQ]

As for generalizing the pattern, observers also work on Event types, so that's something this could tackle 🤔

[MiniaczQ]

Not super sold on the From, instead of having a:

graph TD
  base --base event--> pluginA
  base --base event--> pluginB
  pluginA --> game
  pluginB --> game

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we create this dependency abomination

graph TD
  base --base event--> pluginA
  base --base event--> pluginB
  pluginA --event A--> base
  pluginB --event B--> base
  pluginA --> game
  pluginB --> game

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