Function deserialize_ref_mut 

pub fn deserialize_ref_mut<'de, D, T>(
    deserializer: D,
) -> Result<&'static mut T, D::Error>
where
    D: Deserializer<'de>,
    T: DeserializeOwned + Debug,

deserialize_ref_mut is similar to deserialize_ref, except it operates on a mutable reference instead of an immutable one.