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[Merged by Bors] - Use ManuallyDrop instead of forget in insert_resource_with_id #2947

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[Merged by Bors] - Use ManuallyDrop instead of forget in insert_resource_with_id #2947

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7 changes: 4 additions & 3 deletions crates/bevy_ecs/src/world/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ use crate::{
use std::{
any::TypeId,
fmt,
mem::ManuallyDrop,
sync::atomic::{AtomicU32, Ordering},
};

Expand Down Expand Up @@ -999,13 +1000,13 @@ impl World {
/// # Safety
/// `component_id` must be valid and correspond to a resource component of type T
#[inline]
unsafe fn insert_resource_with_id<T>(&mut self, component_id: ComponentId, mut value: T) {
unsafe fn insert_resource_with_id<T>(&mut self, component_id: ComponentId, value: T) {
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This no longer needing mut T is really nice; it makes me much more confident in the semantics of the change being correct.

let change_tick = self.change_tick();
let column = self.initialize_resource_internal(component_id);
if column.is_empty() {
let mut value = ManuallyDrop::new(value);
// SAFE: column is of type T and has been allocated above
let data = (&mut value as *mut T).cast::<u8>();
std::mem::forget(value);
let data = (&mut *value as *mut T).cast::<u8>();
column.push(data, ComponentTicks::new(change_tick));
} else {
// SAFE: column is of type T and has already been allocated
Expand Down