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Simplify the implementation of UnsafeWorldCell #8727

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Simplify the implementation of UnsafeWorldCell #8727

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9ea2a0f
simplify the implementation of `UnsafeWorldCell`
joseph-gio May 31, 2023
75dfa39
add a clarification to the safety comment
joseph-gio May 31, 2023
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27 changes: 13 additions & 14 deletions crates/bevy_ecs/src/world/unsafe_world_cell.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,8 @@ use crate::{
system::Resource,
};
use bevy_ptr::Ptr;
use std::{any::TypeId, cell::UnsafeCell, marker::PhantomData};
use bevy_utils::syncunsafecell::SyncUnsafeCell;
use std::any::TypeId;

/// Variant of the [`World`] where resource and component accesses take `&self`, and the responsibility to avoid
/// aliasing violations are given to the caller instead of being checked at compile-time by rust's unique XOR shared rule.
Expand Down Expand Up @@ -71,24 +72,22 @@ use std::{any::TypeId, cell::UnsafeCell, marker::PhantomData};
/// }
/// ```
#[derive(Copy, Clone)]
pub struct UnsafeWorldCell<'w>(*mut World, PhantomData<(&'w World, &'w UnsafeCell<World>)>);

// SAFETY: `&World` and `&mut World` are both `Send`
unsafe impl Send for UnsafeWorldCell<'_> {}
// SAFETY: `&World` and `&mut World` are both `Sync`
unsafe impl Sync for UnsafeWorldCell<'_> {}
pub struct UnsafeWorldCell<'w>(&'w SyncUnsafeCell<World>);

impl<'w> UnsafeWorldCell<'w> {
/// Creates a [`UnsafeWorldCell`] that can be used to access everything immutably
/// Creates an [`UnsafeWorldCell`] that can be used to access everything immutably.
#[inline]
pub(crate) fn new_readonly(world: &'w World) -> Self {
UnsafeWorldCell(world as *const World as *mut World, PhantomData)
// SAFETY: `SyncUnsafeCell<World>` has the same representation as `World`,
// so we can safely cast the latter to the former.
// The caller is forbidden from mutating the world with the returned value.
Self(unsafe { &*(world as *const _ as *const _) })
}

/// Creates [`UnsafeWorldCell`] that can be used to access everything mutably
/// Creates an [`UnsafeWorldCell`] that can be used to access everything mutably.
#[inline]
pub(crate) fn new_mutable(world: &'w mut World) -> Self {
Self(world as *mut World, PhantomData)
Self(SyncUnsafeCell::from_mut(world))
}

/// Gets a mutable reference to the [`World`] this [`UnsafeWorldCell`] belongs to.
Expand Down Expand Up @@ -138,7 +137,7 @@ impl<'w> UnsafeWorldCell<'w> {
pub unsafe fn world_mut(self) -> &'w mut World {
// SAFETY:
// - caller ensures the created `&mut World` is the only borrow of world
unsafe { &mut *self.0 }
unsafe { &mut *self.0.get() }
}

/// Gets a reference to the [`&World`](crate::world::World) this [`UnsafeWorldCell`] belongs to.
Expand All @@ -154,7 +153,7 @@ impl<'w> UnsafeWorldCell<'w> {
// - caller ensures there is no `&mut World` this makes it okay to make a `&World`
// - caller ensures there is no mutable borrows of world data, this means the caller cannot
// misuse the returned `&World`
unsafe { &*self.0 }
unsafe { &*self.0.get() }
}

/// Gets a reference to the [`World`] this [`UnsafeWorldCell`] belong to.
Expand Down Expand Up @@ -187,7 +186,7 @@ impl<'w> UnsafeWorldCell<'w> {
// SAFETY:
// - caller ensures that the returned `&World` is not used in a way that would conflict
// with any existing mutable borrows of world data
unsafe { &*self.0 }
unsafe { &*self.0.get() }
}

/// Retrieves this world's unique [ID](WorldId).
Expand Down