Constants and Static Variables

Snippet

Constants and Static Variables

Constants (const) are immutable at compile time with no fixed memory address. Static variables (static) have a fixed memory address and live for the program's entire lifetime. Accessing mutable statics requires unsafe blocks because of data races.

snippet.rs

rust

const MAX_SCORE: i32 = 100;
static GAME_NAME: &str = "RustQuiz";
static mut COUNTER: u32 = 0;
 
fn main() {
    println!("Max score: {}", MAX_SCORE);
    println!("Game: {}", GAME_NAME);
    
    unsafe {
        COUNTER += 1;
        println!("Counter: {}", COUNTER);
    }
}

Breakdown

const MAX_SCORE: i32 = 100;

Compile-time constant, inlined everywhere it's used

static GAME_NAME: &str

Static has fixed memory address for program lifetime

static mut COUNTER: u32 = 0;

Mutable static requires unsafe to access

unsafe { ... }

Unsafe block needed to modify mutable static

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Constants and Static Variables

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