Function get_or_else

pub fn get_or_else<T, F, HashFn, R>(
    hash: &HashFn,
    key: &[u8],
    default_value: F,
) -> T
where
    T: Decode + Sized,
    F: FnOnce() -> T,
    HashFn: Fn(&[u8]) -> R,
    R: AsRef<[u8]>,

Return the value of the item in storage under key, or default_value() if there is no explicit entry.