A static field is a Rust value stored at a fixed memory location for the entire program lifetime. Declare it with an explicit type, usually outside main, and write its name in uppercase. Unlike const, a static may not be created at compile time. section 2.3
Static fields provide several practical guarantees:
- Access them from anywhere in the program, including functions that receive no argument. section 2.3
- Keep them alive for the whole program and avoid ordinary ownership or dropping concerns. section 2.3 section 2.11
- Use a fixed memory location when that distinction matters; use const for values that are compile-time and unchangeable. section 2.3
A program-wide static value
static SEASONS: [&str; 4] = ["Spring", "Summer", "Fall", "Winter"]; fn print_months() { println!("Number of months in the year: {NUMBER_OF_MONTHS}"); } const NUMBER_OF_MONTHS: u32 = 12; fn main() { print_months(); } The function can use the global value without receiving it as an argument. Values such as these are convenient, but they must be known in a form Rust can create without runtime heap allocation. section 2.3
A mutable static, written static mut, can change directly only inside unsafe code. Concurrent access can create aliasing violations or data races, producing undefined behavior. A ten-thread counter may appear correct, while a larger run loses increments; synchronized types such as Arc<Mutex> provide controlled access instead. section 16.4.2
const NUMBER_OF_MONTHS: u32 = 12; static SEASONS: [&str; 4] = ["Spring", "Summer", "Fall", "Winter"];
Use this minimal listing to compare the explicit declarations and uppercase naming convention for const and static values. section 2.3
