`Option<T> -> Result<Option<U>, E>`

map_result.rs

trait Hoge<T> {
    fn map_result<U, E, F>(self, f: F) -> Result<Option<U>, E>
    where
        F: FnOnce(T) -> Result<U, E>;
}

impl<T> Hoge<T> for Option<T> {
    fn map_result<U, E, F>(self, f: F) -> Result<Option<U>, E>
    where
        F: FnOnce(T) -> Result<U, E>,
    {
        match self {
            Some(x) => Ok(Some(f(x)?)),
            None => Ok(None),
        }
    }
}