Error code E0594

A non-mutable value was assigned a value.

Erroneous code example:

#![allow(unused)] fn main() { struct SolarSystem { earth: i32, } let ss = SolarSystem { earth: 3 }; ss.earth = 2; // error! }

To fix this error, declare ss as mutable by using the mut keyword:

#![allow(unused)] fn main() { struct SolarSystem { earth: i32, } let mut ss = SolarSystem { earth: 3 }; // declaring `ss` as mutable ss.earth = 2; // ok! }