# Objective
- Often in games you will want to create chains of systems that modify
some event. For example, a chain of damage systems that handle a
DamageEvent and modify the underlying value before the health system
finally consumes the event. Right now this requires either:
* Using a component added to the entity
* Consuming and refiring events
Neither is ideal when really all we want to do is read the events value,
modify it, and write it back.
## Solution
- Create an EventMutator class similar to EventReader but with ResMut<T>
and iterators that return &mut so that events can be mutated.
## Testing
- I replicated all the existing tests for EventReader to make sure
behavior was the same (I believe) and added a number of tests specific
to testing that 1) events can actually be mutated, and that 2)
EventReader sees changes from EventMutator for events it hasn't already
seen.
## Migration Guide
Users currently using `ManualEventReader` should use `EventCursor`
instead. `ManualEventReader` will be removed in Bevy 0.16. Additionally,
`Events::get_reader` has been replaced by `Events::get_cursor`.
Users currently directly accessing the `Events` resource for mutation
should move to `EventMutator` if possible.
---------
Co-authored-by: poopy <gonesbird@gmail.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
# Objective
- Example `send_and_receive_events` added in #11574 panics
```
thread 'Compute Task Pool (3)' panicked at bevy/crates/bevy_ecs/src/system/system_param.rs:570:17:
Resource requested by send_and_receive_events::read_and_write_different_event_types does not exist: bevy_ecs::event::Events<send_and_receive_events::A>
Encountered a panic in system `send_and_receive_events::read_and_write_different_event_types`!
Encountered a panic in system `bevy_app::main_schedule::Main::run_main`!
```
## Solution
- Register the events used in the system
- Don't use logger as it's not setup with `MinimalPlugins`, just print
---------
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Kanabenki <lucien.menassol@gmail.com>
# Objective
- Sending and receiving events of the same type in the same system is a
reasonably common need, generally due to event filtering.
- However, actually doing so is non-trivial, as the borrow checker
simultaneous hates mutable and immutable access.
## Solution
- Demonstrate two sensible patterns for doing so.
- Update the `ManualEventReader` docs to be more clear and link to this
example.
---------
Co-authored-by: Alice Cecile <alice.i.cecil@gmail.com>
Co-authored-by: Joona Aalto <jondolf.dev@gmail.com>
Co-authored-by: ickk <git@ickk.io>