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# Objective
Change detection can be spuriously triggered by setting a field to the same value as before. As a result, a common pattern is to write:
```rust
if *foo != value {
*foo = value;
}
```
This is confusing to read, and heavy on boilerplate.
Adopted from #5373, but untangled and rebased to current `bevy/main`.
## Solution
1. Add a method to the `DetectChanges` trait that implements this boilerplate when the appropriate trait bounds are met.
2. Document this minor footgun, and point users to it.
## Changelog
* added the `set_if_neq` method to avoid triggering change detection when the new and previous values are equal. This will work on both components and resources.
## Migration Guide
If you are manually checking if a component or resource's value is equal to its new value before setting it to avoid triggering change detection, migrate to the clearer and more convenient `set_if_neq` method.
## Context
Related to #2363 as it avoids triggering change detection, but not a complete solution (as it still requires triggering it when real changes are made).
Co-authored-by: Zoey <Dessix@Dessix.net>
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|---|---|---|
| .. | ||
| component_change_detection.rs | ||
| custom_query_param.rs | ||
| ecs_guide.rs | ||
| event.rs | ||
| fixed_timestep.rs | ||
| generic_system.rs | ||
| hierarchy.rs | ||
| iter_combinations.rs | ||
| parallel_query.rs | ||
| removal_detection.rs | ||
| startup_system.rs | ||
| state.rs | ||
| system_closure.rs | ||
| system_param.rs | ||
| system_piping.rs | ||
| system_sets.rs | ||
| timers.rs | ||