Macro StoredKey 

macro_rules! StoredKey {
    ($key_name:ident, Value = $val:ty, Path = $path:expr, Default = $default:expr, Serialize = $serialize:expr, Deserialize = $deserialize:expr) => { ... };
}

Example usage:

struct ExampleKey;

StoredKey! {
    ExampleKey,
    Value = i32,
    Path = "somedir",
    Default = 1111_i32,
    Serialize = |val: &i32| val.to_string().into_bytes(),
    Deserialize = |contents: &[u8]| {
        String::from_utf8(contents.to_vec())
            .unwrap()
            .parse()
            .unwrap()
    }
}