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42 lines
1.1 KiB
Markdown
42 lines
1.1 KiB
Markdown
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---
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minutes: 5
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---
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# `static`
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Static variables will live during the whole execution of the program, and
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therefore will not move:
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```rust,editable
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static BANNER: &str = "Welcome to RustOS 3.14";
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fn main() {
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println!("{BANNER}");
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}
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```
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As noted in the [Rust RFC Book][1], these are not inlined upon use and have an
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actual associated memory location. This is useful for unsafe and embedded code,
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and the variable lives through the entirety of the program execution. When a
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globally-scoped value does not have a reason to need object identity, `const` is
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generally preferred.
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<details>
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- `static` is similar to mutable global variables in C++.
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- `static` provides object identity: an address in memory and state as required
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by types with interior mutability such as `Mutex<T>`.
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# More to Explore
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Because `static` variables are accessible from any thread, they must be `Sync`.
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Interior mutability is possible through a
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[`Mutex`](https://doc.rust-lang.org/std/sync/struct.Mutex.html), atomic or
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similar.
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Thread-local data can be created with the macro `std::thread_local`.
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</details>
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[1]: https://rust-lang.github.io/rfcs/0246-const-vs-static.html
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