Error code E0384

An immutable variable was reassigned.

Erroneous code example:

fn main() { let x = 3; x = 5; // error, reassignment of immutable variable }

By default, variables in Rust are immutable. To fix this error, add the keyword mut after the keyword let when declaring the variable. For example:

fn main() { let mut x = 3; x = 5; }