errors6.rs

[zzz6519003]

// errors6.rs

// Using catch-all error types like Box<dyn error::Error> isn't recommended // for library code, where callers might want to make decisions based on the // error content, instead of printing it out or propagating it further. Here, // we define a custom error type to make it possible for callers to decide // what to do next when our function returns an error.

// Execute rustlings hint errors6 or use the hint watch subcommand for a hint.

use std::num::ParseIntError;

// This is a custom error type that we will be using in parse_pos_nonzero().

[derive(PartialEq, Debug)]

enum ParsePosNonzeroError { Creation(CreationError), ParseInt(ParseIntError), }

impl ParsePosNonzeroError { fn from_creation(err: CreationError) -> ParsePosNonzeroError { ParsePosNonzeroError::Creation(err) } // TODO: add another error conversion function here. fn from_parseint(err: ParseIntError) -> ParsePosNonzeroError { ParsePosNonzeroError::ParseInt(err) } }

fn parse_pos_nonzero(s: &str) -> Result<PositiveNonzeroInteger, ParsePosNonzeroError> { // TODO: change this to return an appropriate error instead of panicking // when parse() returns an error. // let x: i64 = s.parse().unwrap(); // PositiveNonzeroInteger::new(x).map_err(ParsePosNonzeroError::from_creation) match s.parse() { Ok(n) => { match PositiveNonzeroInteger::new(n) { Ok(n) => Ok(n), Err(err) => Err(ParsePosNonzeroError::from_creation(err)) } } Err(err) => { Err(ParsePosNonzeroError::from_parseint(err)) } } }

// Don't change anything below this line.

[derive(PartialEq, Debug)]

struct PositiveNonzeroInteger(u64);

[derive(PartialEq, Debug)]

enum CreationError { Negative, Zero, }

impl PositiveNonzeroInteger { fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> { match value { x if x < 0 => Err(CreationError::Negative), x if x == 0 => Err(CreationError::Zero), x => Ok(PositiveNonzeroInteger(x as u64)), } } }

[cfg(test)]

mod test { use super::*;

#[test]
fn test_parse_error() {
    // We can't construct a ParseIntError, so we have to pattern match.
    assert!(matches!(
        parse_pos_nonzero("not a number"),
        Err(ParsePosNonzeroError::ParseInt(_))
    ));
}

#[test]
fn test_negative() {
    assert_eq!(
        parse_pos_nonzero("-555"),
        Err(ParsePosNonzeroError::Creation(CreationError::Negative))
    );
}

#[test]
fn test_zero() {
    assert_eq!(
        parse_pos_nonzero("0"),
        Err(ParsePosNonzeroError::Creation(CreationError::Zero))
    );
}

#[test]
fn test_positive() {
    let x = PositiveNonzeroInteger::new(42);
    assert!(x.is_ok());
    assert_eq!(parse_pos_nonzero("42"), Ok(x.unwrap()));
}

}