Rust by Example

Rust has two different types of constants which can be declared in any scope including global. Both require explicit type annotation:

• const: An unchangeable value (the common case).

• static: A possibly mutable variable with 'static lifetime. The static lifetime is inferred and does not have to be specified. Accessing or modifying a mutable static variable is unsafe.

// Globals are declared outside all other scopes.

static LANGUAGE: &str = "Rust";

const THRESHOLD: i32 = 10;

fn is_big(n: i32) -> bool {

// Access constant in some function

n > THRESHOLD

}

fn main() {

let n = 16;

// Access constant in the main thread

println!("This is {}", LANGUAGE);

println!("The threshold is {}", THRESHOLD);

println!("{} is {}", n, if is_big(n) { "big" } else { "small" });

// Error! Cannot modify a `const`.

THRESHOLD = 5;

// FIXME ^ Comment out this line

}

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