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Merged
merged 4 commits into from
Jan 25, 2025
Merged

distinct 'static' items never overlap #1657

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c96c0a7
attempt to clarify 'static' unique address guarantees
RalfJung Oct 20, 2024
8dde3eb
add a ZST exception
RalfJung Nov 7, 2024
0b7d4f7
clarify wording
RalfJung Nov 20, 2024
08688f1
there are no heap-allocated variables
RalfJung Jan 18, 2025
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21 changes: 14 additions & 7 deletions src/items/static-items.md
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Expand Up @@ -12,21 +12,27 @@ r[items.static.syntax]
> allowed semantically within `extern` blocks.

r[items.static.intro]
A *static item* is similar to a [constant], except that it represents a precise
memory location in the program. All references to the static refer to the same
memory location.
A *static item* is similar to a [constant], except that it represents an allocated object in the
program that is initialized with the initializer expression. All references and raw pointers to the
static refer to the same allocated object.

r[items.static.lifetime]
Static items have the `static` lifetime, which outlives all
other lifetimes in a Rust program. Static items do not call [`drop`] at the
end of the program.
Static items have the `static` lifetime, which outlives all other lifetimes in a Rust program.
Static items do not call [`drop`] at the end of the program.

r[items.static.storage-disjointness]
If the `static` has a size of at least 1 byte, this allocated object is disjoint from all other
`static` objects as well as heap-allocated and stack-allocated variables. However, the storage of
immutable `static` items can overlap with objects that do not themselves have a unique address, such
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“Immutable static item” could be interpreted as meaning a static item without the mut keyword, but it must also exclude interior-mutable memory. Perhaps this should be clarified (or perhaps it doesn’t matter since this is a “can”, not “must”).

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Yes we should have this as a shared definition somewhere that we can reference.

as [promoteds] and [`const` items][constant].

r[items.static.namespace]
The static declaration defines a static value in the [value namespace] of the module or block where it is located.

r[items.static.init]
The static initializer is a [constant expression] evaluated at compile time.
Static initializers may refer to other statics.
Static initializers may refer to and read from other statics.
When reading from mutable statics, they read the initial value of that static.

r[items.static.read-only]
Non-`mut` static items that contain a type that is not [interior mutable] may
Expand Down Expand Up @@ -173,3 +179,4 @@ following are true:
[_Expression_]: ../expressions.md
[value namespace]: ../names/namespaces.md
[_ItemSafety_]: functions.md
[promoteds]: ../destructors.md#constant-promotion