# Objective
sending events tends to be low-frequency so ergonomics can be
prioritized over efficiency.
add `Commands::send_event` to send any type of event without needing a
writer in hand.
i don't know how we feel about these kind of ergonomic things, i add
this to all my projects and find it useful. adding `mut
this_particular_event_writer: EventWriter<ThisParticularEvent>` every
time i want to send something is unnecessarily cumbersome.
it also simplifies the "send and receive in the same system" pattern
significantly.
basic example before:
```rs
fn my_func(
q: Query<(Entity, &State)>,
mut damage_event_writer: EventWriter<DamageEvent>,
mut heal_event_writer: EventWriter<HealEvent>,
) {
for (entity, state) in q.iter() {
if let Some(damage) = state.get_damage() {
damage_event_writer.send(DamageEvent { entity, damage });
}
if let Some(heal) = state.get_heal() {
heal_event_writer.send(HealEvent { entity, heal });
}
}
}
```
basic example after:
```rs
import bevy::ecs::event::SendEventEx;
fn my_func(
mut commands: Commands,
q: Query<(Entity, &State)>,
) {
for (entity, state) in q.iter() {
if let Some(damage) = state.get_damage() {
commands.send_event(DamageEvent { entity, damage });
}
if let Some(heal) = state.get_heal() {
commands.send_event(HealEvent { entity, heal });
}
}
}
```
send/receive in the same system before:
```rs
fn send_and_receive_param_set(
mut param_set: ParamSet<(EventReader<DebugEvent>, EventWriter<DebugEvent>)>,
) {
// We must collect the events to resend, because we can't access the writer while we're iterating over the reader.
let mut events_to_resend = Vec::new();
// This is p0, as the first parameter in the `ParamSet` is the reader.
for event in param_set.p0().read() {
if event.resend_from_param_set {
events_to_resend.push(event.clone());
}
}
// This is p1, as the second parameter in the `ParamSet` is the writer.
for mut event in events_to_resend {
event.times_sent += 1;
param_set.p1().send(event);
}
}
```
after:
```rs
use bevy::ecs::event::SendEventEx;
fn send_via_commands_and_receive(
mut reader: EventReader<DebugEvent>,
mut commands: Commands,
) {
for event in reader.read() {
if event.resend_via_commands {
commands.send_event(DebugEvent {
times_sent: event.times_sent + 1,
..event.clone()
});
}
}
}
```
---------
Co-authored-by: Jan Hohenheim <jan@hohenheim.ch>
45281e62d7