064e5e48b4
# Objective `Entity::PLACEHOLDER` acts as a magic number that will *probably* never really exist, but it certainly could. And, `Entity` has a niche, so the only reason to use `PLACEHOLDER` is as an alternative to `MaybeUninit` that trades safety risks for logic risks. As a result, bevy has generally advised against using `PLACEHOLDER`, but we still use if for a lot internally. This pr starts removing internal uses of it, starting from observers. ## Solution Change all trigger target related types from `Entity` to `Option<Entity>` Small migration guide to come. ## Testing CI ## Future Work This turned a lot of code from ```rust trigger.target() ``` to ```rust trigger.target().unwrap() ``` The extra panic is no worse than before; it's just earlier than panicking after passing the placeholder to something else. But this is kinda annoying. I would like to add a `TriggerMode` or something to `Event` that would restrict what kinds of targets can be used for that event. Many events like `Removed` etc, are always triggered with a target. We can make those have a way to assume Some, etc. But I wanted to save that for a future pr.
13 lines
651 B
Markdown
13 lines
651 B
Markdown
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title: Observer Triggers
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pull_requests: [19440]
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---
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Observers may be triggered on particular entities or globally.
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Previously, a global trigger would claim to trigger on a particular `Entity`, `Entity::PLACEHOLDER`.
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For correctness and transparency, triggers have been changed to `Option<Entity>`.
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`Trigger::target` now returns `Option<Entity>` and `ObserverTrigger::target` is now of type `Option<Entity>`.
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If you were checking for `Entity::PLACEHOLDER`, migrate to handling the `None` case.
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If you were not checking for `Entity::PLACEHOLDER`, migrate to unwrapping, as `Entity::PLACEHOLDER` would have caused a panic before, at a later point.
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