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use std::convert::Infallible;

/// A type that can indicate something is not found.
/// Implement this on `E` to get the `.optional()?` function on the `Result<T, E>` type.
pub trait IsNotFoundError {
    fn is_not_found_error(&self) -> bool;
}

pub trait Optional<T> {
    type Error;

    fn optional(self) -> Result<Option<T>, Self::Error>;
}

impl<T, E: IsNotFoundError> Optional<T> for Result<T, E> {
    type Error = E;

    fn optional(self) -> Result<Option<T>, Self::Error> {
        match self {
            Ok(t) => Ok(Some(t)),
            Err(e) if e.is_not_found_error() => Ok(None),
            Err(e) => Err(e),
        }
    }
}

impl IsNotFoundError for Infallible {
    fn is_not_found_error(&self) -> bool {
        false
    }
}
