Rust macro for mutate immutable variables

mutate.rs

macro_rules! mutate {
    ($($var:ident),+ $code:block) => {
        let ($($var,)+) = {
            let ($(mut $var,)+) = ($($var,)+);
            $code;
            ($($var,)+)
        };
    };
}

#[cfg(test)]
mod tests {
    #[test]
    fn can_mutate_single() {
        let s = String::new(); // s is immutable empty String
        mutate!(s { s.push_str("test"); }); // mutate in macro
        assert_eq!("test", &s[..]);
    }

    #[test]
    fn can_mutate_multy() {
        let s0 = String::new();
        let s1 = String::new();
        mutate!(s0, s1 {
            s0.push_str("test0");
            s1.push_str("test1");
        });
        assert_eq!("test0", &s0[..]);
        assert_eq!("test1", &s1[..]);
    }
}