4.1 Mutability
Variables are immutable by default, but this can be overridden using the mut
modifier.
fn main() {
let _immutable_variable = 1;
let mut mutable_variable = 1;
println!("Before mutation: {}", mutable_variable);
// Ok
mutable_variable += 1;
println!("After mutation: {}", mutable_variable);
// Error!
_immutable_variable += 1;
// FIXME ^ Comment out this line
}
The compiler will throw a detailed diagnostic about mutability errors.