Değişebilir Statik Değişkenler
It is safe to read an immutable static variable:
static HELLO_WORLD: &str = "Merhaba, dünya!"; fn main() { println!("HELLO_WORLD: {HELLO_WORLD}"); }
However, since data races can occur, it is unsafe to read and write mutable static variables:
static mut COUNTER: u32 = 0; fn add_to_counter(inc: u32) { // SAFETY: There are no other threads which could be accessing `COUNTER`. unsafe { COUNTER += inc; } } fn main() { add_to_counter(42); // SAFETY: There are no other threads which could be accessing `COUNTER`. unsafe { println!("COUNTER: {COUNTER}"); } }
This slide should take about 5 minutes.
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The program here is safe because it is single-threaded. However, the Rust compiler is conservative and will assume the worst. Try removing the
unsafe
and see how the compiler explains that it is undefined behavior to mutate a static from multiple threads. -
Using a mutable static is generally a bad idea, but there are some cases where it might make sense in low-level
no_std
code, such as implementing a heap allocator or working with some C APIs.