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@jordanorelli
Created September 3, 2022 16:08
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// 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)
}
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.
// we started with this:
// let x: i64 = s.parse().unwrap();
// this is also a solution:
// let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parseint)?;
// this is one valid solution
let x = match s.parse::<i64>() {
Ok(n) => n,
Err(e) => return Err(ParsePosNonzeroError::from_parseint(e)),
};
PositiveNonzeroInteger::new(x)
.map_err(ParsePosNonzeroError::from_creation)
}
// 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()));
}
}
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