medium.learning_rust.error_handling.custom_error_type..rs

use std::fmt;

struct CustomErr(isize);

// Implement std::fmt::Display for CustomErr
impl fmt::Display for CustomErr {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.user_face_err())
    }
}

// Implement std::fmt::Debug for CustomErr
impl fmt::Debug for CustomErr {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.programmer_face_err())
    }
}

impl CustomErr {
    // Handle user-facing output
    fn user_face_err(&self) -> &str {
        let CustomErr(err_code) = self;

        let err_msg = match err_code {
            404 => "Sorry, Can not find the Page!",
            _ => "Sorry, something is wrong! Please Try Again!",
        };

        err_msg
    }

    // Handle programmer-facing output
    fn programmer_face_err(&self) -> &str {
        let CustomErr(err_code) = self;

        let err_msg = match err_code {
            404 => "CustomErr {{ code: 404, message: Not found }}",
            _ => "CustomErr {{ code: n/a }} ",
        };

        err_msg
    }
}

// A sample function to produce an CustomErr Err
fn produce_error() -> Result<(), CustomErr> {
    Err(CustomErr(404))
}

fn main() {
    match produce_error() {
        Err(e) => eprintln!("{}", e), // Sorry, Can not find the Page!
        _ => println!("No error"),
    }

    eprintln!("{:?}", produce_error()); // Err(CustomErr {{ code: 404, message: Not found }})

    eprintln!("{:#?}", produce_error());
    // Err(
    //     CustomErr {{ code: 404, message: Not found }}
    // )
}