rustlings/exercises/13_error_handling/errors6.rs

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// Using catch-all error types like `Box<dyn 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.
use std::num::ParseIntError;
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#[derive(PartialEq, Debug)]
enum CreationError {
Negative,
Zero,
}
// A custom error type that we will be using in `PositiveNonzeroInteger::parse`.
#[derive(PartialEq, Debug)]
enum ParsePosNonzeroError {
Creation(CreationError),
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ParseInt(ParseIntError),
}
impl ParsePosNonzeroError {
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fn from_creation(err: CreationError) -> Self {
Self::Creation(err)
}
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// TODO: Add another error conversion function here.
// fn from_parseint(???) -> Self { ??? }
}
#[derive(PartialEq, Debug)]
struct PositiveNonzeroInteger(u64);
impl PositiveNonzeroInteger {
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fn new(value: i64) -> Result<Self, CreationError> {
match value {
x if x < 0 => Err(CreationError::Negative),
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0 => Err(CreationError::Zero),
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x => Ok(Self(x as u64)),
}
}
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fn parse(s: &str) -> Result<Self, ParsePosNonzeroError> {
// TODO: change this to return an appropriate error instead of panicking
// when `parse()` returns an error.
let x: i64 = s.parse().unwrap();
Self::new(x).map_err(ParsePosNonzeroError::from_creation)
}
}
fn main() {
// You can optionally experiment here.
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_parse_error() {
assert!(matches!(
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PositiveNonzeroInteger::parse("not a number"),
Err(ParsePosNonzeroError::ParseInt(_)),
));
}
#[test]
fn test_negative() {
assert_eq!(
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PositiveNonzeroInteger::parse("-555"),
Err(ParsePosNonzeroError::Creation(CreationError::Negative)),
);
}
#[test]
fn test_zero() {
assert_eq!(
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PositiveNonzeroInteger::parse("0"),
Err(ParsePosNonzeroError::Creation(CreationError::Zero)),
);
}
#[test]
fn test_positive() {
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let x = PositiveNonzeroInteger::new(42).unwrap();
assert_eq!(x.0, 42);
assert_eq!(PositiveNonzeroInteger::parse("42"), Ok(x));
}
}