Enum DoubleError

0a_error_handling/rust/using_eyre/src/bin/thiserror.rs:5–10

#[derive(Error, Debug)]
enum DoubleError {
    #[error("no first item")]
    EmptyVec,
    #[error("invalid first item, error: '{0}'")]
    Parse(#[from] std::num::ParseIntError),
}

fn double_first(vec: Vec<&str>) -> Result<i32> {
    let first = vec.first().ok_or(DoubleError::EmptyVec)?;