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93 lines
2.4 KiB
Rust
93 lines
2.4 KiB
Rust
// Using catch-all error types like `Box<dyn Error>` isn't recommended for
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// library code where callers might want to make decisions based on the error
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// content instead of printing it out or propagating it further. Here, we define
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// a custom error type to make it possible for callers to decide what to do next
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// when our function returns an error.
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use std::num::ParseIntError;
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#[derive(PartialEq, Debug)]
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enum CreationError {
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Negative,
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Zero,
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}
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// A custom error type that we will be using in `PositiveNonzeroInteger::parse`.
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#[derive(PartialEq, Debug)]
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enum ParsePosNonzeroError {
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Creation(CreationError),
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ParseInt(ParseIntError),
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}
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impl ParsePosNonzeroError {
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fn from_creation(err: CreationError) -> Self {
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Self::Creation(err)
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}
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fn from_parseint(err: ParseIntError) -> Self {
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Self::ParseInt(err)
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}
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}
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#[derive(PartialEq, Debug)]
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struct PositiveNonzeroInteger(u64);
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impl PositiveNonzeroInteger {
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fn new(value: i64) -> Result<Self, CreationError> {
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match value {
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x if x < 0 => Err(CreationError::Negative),
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x if x == 0 => Err(CreationError::Zero),
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x => Ok(Self(x as u64)),
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}
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}
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fn parse(s: &str) -> Result<Self, ParsePosNonzeroError> {
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// Return an appropriate error instead of panicking when `parse()`
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// returns an error.
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let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parseint)?;
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// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Self::new(x).map_err(ParsePosNonzeroError::from_creation)
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}
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}
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fn main() {
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// You can optionally experiment here.
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}
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#[cfg(test)]
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mod test {
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use super::*;
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use std::num::IntErrorKind;
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#[test]
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fn test_parse_error() {
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assert!(matches!(
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PositiveNonzeroInteger::parse("not a number"),
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Err(ParsePosNonzeroError::ParseInt(_)),
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));
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}
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#[test]
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fn test_negative() {
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assert_eq!(
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PositiveNonzeroInteger::parse("-555"),
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Err(ParsePosNonzeroError::Creation(CreationError::Negative)),
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);
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}
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#[test]
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fn test_zero() {
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assert_eq!(
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PositiveNonzeroInteger::parse("0"),
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Err(ParsePosNonzeroError::Creation(CreationError::Zero)),
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);
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}
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#[test]
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fn test_positive() {
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let x = PositiveNonzeroInteger::new(42).unwrap();
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assert_eq!(x.0, 42);
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assert_eq!(PositiveNonzeroInteger::parse("42"), Ok(x));
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}
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}
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