address review feedback
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.
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@ -43,8 +43,8 @@ impl PositiveNonzeroInteger {
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impl fmt::Display for CreationError {
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impl fmt::Display for CreationError {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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let description = match *self {
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let description = match *self {
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CreationError::Negative => "Number is negative",
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CreationError::Negative => "number is negative",
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CreationError::Zero => "Number is zero",
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CreationError::Zero => "number is zero",
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};
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};
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f.write_str(description)
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f.write_str(description)
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}
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}
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@ -10,11 +10,20 @@
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// I AM NOT DONE
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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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// 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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#[derive(PartialEq, Debug)]
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enum ParsePosNonzeroError {
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enum ParsePosNonzeroError {
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CreationError,
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Creation(CreationError),
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ParseIntError
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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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}
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fn parse_pos_nonzero(s: &str)
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fn parse_pos_nonzero(s: &str)
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@ -24,7 +33,7 @@ fn parse_pos_nonzero(s: &str)
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// when `parse()` returns an error.
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// when `parse()` returns an error.
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let x: i64 = s.parse().unwrap();
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let x: i64 = s.parse().unwrap();
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PositiveNonzeroInteger::new(x)
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PositiveNonzeroInteger::new(x)
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.or(Err(ParsePosNonzeroError::CreationError))
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.map_err(ParsePosNonzeroError::from_creation)
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}
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}
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// Don't change anything below this line.
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// Don't change anything below this line.
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@ -54,17 +63,18 @@ mod test {
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#[test]
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#[test]
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fn test_parse_error() {
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fn test_parse_error() {
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assert_eq!(
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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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parse_pos_nonzero("not a number"),
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Err(ParsePosNonzeroError::ParseIntError)
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Err(ParsePosNonzeroError::ParseInt(_))
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);
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));
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}
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}
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#[test]
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#[test]
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fn test_negative() {
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fn test_negative() {
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assert_eq!(
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assert_eq!(
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parse_pos_nonzero("-555"),
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parse_pos_nonzero("-555"),
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Err(ParsePosNonzeroError::CreationError)
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Err(ParsePosNonzeroError::Creation(CreationError::Negative))
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);
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);
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}
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}
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@ -72,15 +82,14 @@ mod test {
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fn test_zero() {
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fn test_zero() {
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assert_eq!(
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assert_eq!(
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parse_pos_nonzero("0"),
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parse_pos_nonzero("0"),
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Err(ParsePosNonzeroError::CreationError)
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Err(ParsePosNonzeroError::Creation(CreationError::Zero))
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);
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);
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}
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}
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#[test]
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#[test]
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fn test_positive() {
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fn test_positive() {
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assert_eq!(
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let x = PositiveNonzeroInteger::new(42);
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parse_pos_nonzero("42"),
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assert!(x.is_ok());
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Ok(PositiveNonzeroInteger(42))
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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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}
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}
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}
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21
info.toml
21
info.toml
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@ -532,16 +532,19 @@ path = "exercises/error_handling/errors6.rs"
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mode = "test"
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mode = "test"
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hint = """
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hint = """
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This exercise uses a completed version of `PositiveNonzeroInteger` from
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This exercise uses a completed version of `PositiveNonzeroInteger` from
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the errors4.
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errors4.
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Below the TODO line, there is an example of using the `.or()` method
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Below the line that TODO asks you to change, there is an example of using
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on a `Result` to transform one type of error into another. Try using
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the `map_err()` method on a `Result` to transform one type of error into
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something similar on the `Result` from `parse()`. You might use the `?`
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another. Try using something similar on the `Result` from `parse()`. You
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operator to return early from the function, or you might use a `match`
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might use the `?` operator to return early from the function, or you might
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expression, or maybe there's another way!
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use a `match` expression, or maybe there's another way!
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Read more about `.or()` in the `std::result` documentation:
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You can create another function inside `impl ParsePosNonzeroError` to use
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https://doc.rust-lang.org/std/result/enum.Result.html#method.or"""
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with `map_err()`.
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Read more about `map_err()` in the `std::result` documentation:
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https://doc.rust-lang.org/std/result/enum.Result.html#method.map_err"""
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# Generics
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# Generics
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@ -927,7 +930,7 @@ hint = """
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Follow the steps provided right before the `TryFrom` implementation.
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Follow the steps provided right before the `TryFrom` implementation.
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You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
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You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
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You might want to look back at the exercise errorsn (or its hints) to remind
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You might want to look back at the exercise errors5 (or its hints) to remind
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yourself about how `Box<dyn Error>` works.
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yourself about how `Box<dyn Error>` works.
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If you're trying to return a string as an error, note that neither `str`
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If you're trying to return a string as an error, note that neither `str`
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