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b7ddd09fab
Adjust error text and naming to conform with best practices. Use `map_err()` instead of `or()`. Wrap lower-level errors instead of ignoring their details. Also, don't "cheat" by bypassing the `new()` function in tests. Fix a dangling reference in the try_from_into hints.
96 lines
2.5 KiB
Rust
96 lines
2.5 KiB
Rust
// errors6.rs
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// Using catch-all error types like `Box<dyn error::Error>` isn't recommended
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// for library code, where callers might want to make decisions based on the
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// error content, instead of printing it out or propagating it further. Here,
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// we define a custom error type to make it possible for callers to decide
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// what to do next when our function returns an error.
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// Make these tests pass! Execute `rustlings hint errors6` for hints :)
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// I AM NOT DONE
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use std::num::ParseIntError;
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// This is a custom error type that we will be using in `parse_pos_nonzero()`.
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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) -> ParsePosNonzeroError {
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ParsePosNonzeroError::Creation(err)
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}
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// TODO: add another error conversion function here.
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}
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fn parse_pos_nonzero(s: &str)
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-> Result<PositiveNonzeroInteger, ParsePosNonzeroError>
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{
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// TODO: change this to return an appropriate error instead of panicking
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// when `parse()` returns an error.
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let x: i64 = s.parse().unwrap();
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PositiveNonzeroInteger::new(x)
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.map_err(ParsePosNonzeroError::from_creation)
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}
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// Don't change anything below this line.
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#[derive(PartialEq, Debug)]
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struct PositiveNonzeroInteger(u64);
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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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impl PositiveNonzeroInteger {
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fn new(value: i64) -> Result<PositiveNonzeroInteger, 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(PositiveNonzeroInteger(x as u64))
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}
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}
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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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#[test]
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fn test_parse_error() {
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// We can't construct a ParseIntError, so we have to pattern match.
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assert!(matches!(
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parse_pos_nonzero("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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parse_pos_nonzero("-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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parse_pos_nonzero("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);
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assert!(x.is_ok());
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assert_eq!(parse_pos_nonzero("42"), Ok(x.unwrap()));
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}
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}
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