static

静态变量在程序的整个执行过程中始终有效，因此不会移动：

static BANNER: &str = "Welcome to RustOS 3.14";

fn main() {
    println!("{BANNER}");
}

As noted in the Rust RFC Book, these are not inlined upon use and have an actual associated memory location. This is useful for unsafe and embedded code, and the variable lives through the entirety of the program execution. When a globally-scoped value does not have a reason to need object identity, const is generally preferred.

This slide should take about 5 minutes.
  • static is similar to mutable global variables in C++.
  • static provides object identity: an address in memory and state as required by types with interior mutability such as Mutex<T>.

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Because static variables are accessible from any thread, they must be Sync. Interior mutability is possible through a Mutex, atomic or similar.

Thread-local data can be created with the macro std::thread_local.