Declaring a Constant

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;

References

• Rust by Example
• Rust Book: Variables and Mutability