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Document UnsafeCell special-casing in shared statics #2169

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Document UnsafeCell special-casing in shared statics #2169

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9 changes: 6 additions & 3 deletions src/items/static-items.md
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Expand Up @@ -28,10 +28,13 @@ r[items.static.read-only]
Non-`mut` static items that contain a type that is not [interior mutable] may be placed in read-only memory.

r[items.static.safety]
All access to a static is safe, but there are a number of restrictions on statics:
All access to a static is safe, but the type is restricted, and must either:

r[items.static.sync]
* The type must have the [`Sync`](std::marker::Sync) trait bound to allow thread-safe access.
* Implement the [`Sync`](std::marker::Sync) trait to allow thread-safe access.

r[items.static.unsafecell]
* Be [`UnsafeCell<T>`](std::cell::UnsafeCell), where `T` implements the [`Sync`](std::marker::Sync) trait.

r[items.static.init.omission]
The initializer expression must be omitted in an [external block], and must be provided for free static items.
Expand Down Expand Up @@ -126,7 +129,7 @@ fn bump_levels_safe() -> u32 {
```

r[items.static.mut.sync]
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@madsmtm madsmtm Feb 12, 2026 •
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Unsure about the name of this rule label now.

Mutable statics have the same restrictions as normal statics, except that the type does not have to implement the `Sync` trait.
Mutable statics have the same restrictions as normal statics, except that there are no no restrictions on the type (for example, the type does not have to implement the `Sync` trait).

r[items.static.alternate]
## Using statics or consts
Expand Down