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Merge pull request #781 from tlyu/advanced-errs 

feature: advanced errors
This commit is contained in:
diannasoriel 2021-09-25 11:18:55 +02:00 committed by GitHub
parent 0de45ccdb7 abd6b70c72
commit c2ed98deb3
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5 changed files with 475 additions and 51 deletions
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98
exercises/advanced_errors/advanced_errs1.rs Normal file
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@ -0,0 +1,98 @@
// advanced_errs1.rs
// Remember back in errors6, we had multiple mapping functions so that we
// could translate lower-level errors into our custom error type using
// `map_err()`? What if we could use the `?` operator directly instead?
// Make this code compile! Execute `rustlings hint advanced_errs1` for
// hints :)
// I AM NOT DONE
use std::num::ParseIntError;
use std::str::FromStr;
// This is a custom error type that we will be using in the `FromStr`
// implementation.
#[derive(PartialEq, Debug)]
enum ParsePosNonzeroError {
Creation(CreationError),
ParseInt(ParseIntError),
}
impl From<CreationError> for ParsePosNonzeroError {
fn from(e: CreationError) -> Self {
// TODO: complete this implementation so that the `?` operator will
// work for `CreationError`
}
}
// TODO: implement another instance of the `From` trait here so that the
// `?` operator will work in the other place in the `FromStr`
// implementation below.
// Don't change anything below this line.
impl FromStr for PositiveNonzeroInteger {
type Err = ParsePosNonzeroError;
fn from_str(s: &str) -> Result<PositiveNonzeroInteger, Self::Err> {
let x: i64 = s.parse()?;
Ok(PositiveNonzeroInteger::new(x)?)
}
}
#[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!(
PositiveNonzeroInteger::from_str("not a number"),
Err(ParsePosNonzeroError::ParseInt(_))
));
}
#[test]
fn test_negative() {
assert_eq!(
PositiveNonzeroInteger::from_str("-555"),
Err(ParsePosNonzeroError::Creation(CreationError::Negative))
);
}
#[test]
fn test_zero() {
assert_eq!(
PositiveNonzeroInteger::from_str("0"),
Err(ParsePosNonzeroError::Creation(CreationError::Zero))
);
}
#[test]
fn test_positive() {
let x = PositiveNonzeroInteger::new(42);
assert!(x.is_ok());
assert_eq!(PositiveNonzeroInteger::from_str("42"), Ok(x.unwrap()));
}
}

203
exercises/advanced_errors/advanced_errs2.rs Normal file
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@ -0,0 +1,203 @@
// advanced_errs2.rs
// This exercise demonstrates a few traits that are useful for custom error
// types to implement, especially so that other code can consume the custom
// error type more usefully.
// Make this compile, and make the tests pass!
// Execute `rustlings hint advanced_errs2` for hints.
// Steps:
// 1. Implement a missing trait so that `main()` will compile.
// 2. Complete the partial implementation of `From` for
// `ParseClimateError`.
// 3. Handle the missing error cases in the `FromStr` implementation for
// `Climate`.
// 4. Complete the partial implementation of `Display` for
// `ParseClimateError`.
// I AM NOT DONE
use std::error::Error;
use std::fmt::{self, Display, Formatter};
use std::num::{ParseFloatError, ParseIntError};
use std::str::FromStr;
// This is the custom error type that we will be using for the parser for
// `Climate`.
#[derive(Debug, PartialEq)]
enum ParseClimateError {
Empty,
BadLen,
NoCity,
ParseInt(ParseIntError),
ParseFloat(ParseFloatError),
}
// This `From` implementation allows the `?` operator to work on
// `ParseIntError` values.
impl From<ParseIntError> for ParseClimateError {
fn from(e: ParseIntError) -> Self {
Self::ParseInt(e)
}
}
// This `From` implementation allows the `?` operator to work on
// `ParseFloatError` values.
impl From<ParseFloatError> for ParseClimateError {
fn from(e: ParseFloatError) -> Self {
// TODO: Complete this function
}
}
// TODO: Implement a missing trait so that `main()` below will compile. It
// is not necessary to implement any methods inside the missing trait.
// The `Display` trait allows for other code to obtain the error formatted
// as a user-visible string.
impl Display for ParseClimateError {
// TODO: Complete this function so that it produces the correct strings
// for each error variant.
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
// Imports the variants to make the following code more compact.
use ParseClimateError::*;
match self {
NoCity => write!(f, "no city name"),
ParseFloat(e) => write!(f, "error parsing temperature: {}", e),
_ => write!(f, "unhandled error!"),
}
}
}
#[derive(Debug, PartialEq)]
struct Climate {
city: String,
year: u32,
temp: f32,
}
// Parser for `Climate`.
// 1. Split the input string into 3 fields: city, year, temp.
// 2. Return an error if the string is empty or has the wrong number of
// fields.
// 3. Return an error if the city name is empty.
// 4. Parse the year as a `u32` and return an error if that fails.
// 5. Parse the temp as a `f32` and return an error if that fails.
// 6. Return an `Ok` value containing the completed `Climate` value.
impl FromStr for Climate {
type Err = ParseClimateError;
// TODO: Complete this function by making it handle the missing error
// cases.
fn from_str(s: &str) -> Result<Self, Self::Err> {
let v: Vec<_> = s.split(',').collect();
let (city, year, temp) = match &v[..] {
[city, year, temp] => (city.to_string(), year, temp),
_ => return Err(ParseClimateError::BadLen),
};
let year: u32 = year.parse()?;
let temp: f32 = temp.parse()?;
Ok(Climate { city, year, temp })
}
}
// Don't change anything below this line (other than to enable ignored
// tests).
fn main() -> Result<(), Box<dyn Error>> {
println!("{:?}", "Hong Kong,1999,25.7".parse::<Climate>()?);
println!("{:?}", "".parse::<Climate>()?);
Ok(())
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_empty() {
let res = "".parse::<Climate>();
assert_eq!(res, Err(ParseClimateError::Empty));
assert_eq!(res.unwrap_err().to_string(), "empty input");
}
#[test]
fn test_short() {
let res = "Boston,1991".parse::<Climate>();
assert_eq!(res, Err(ParseClimateError::BadLen));
assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
}
#[test]
fn test_long() {
let res = "Paris,1920,17.2,extra".parse::<Climate>();
assert_eq!(res, Err(ParseClimateError::BadLen));
assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
}
#[test]
fn test_no_city() {
let res = ",1997,20.5".parse::<Climate>();
assert_eq!(res, Err(ParseClimateError::NoCity));
assert_eq!(res.unwrap_err().to_string(), "no city name");
}
#[test]
fn test_parse_int_neg() {
let res = "Barcelona,-25,22.3".parse::<Climate>();
assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
let err = res.unwrap_err();
if let ParseClimateError::ParseInt(ref inner) = err {
assert_eq!(
err.to_string(),
format!("error parsing year: {}", inner.to_string())
);
} else {
unreachable!();
};
}
#[test]
fn test_parse_int_bad() {
let res = "Beijing,foo,15.0".parse::<Climate>();
assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
let err = res.unwrap_err();
if let ParseClimateError::ParseInt(ref inner) = err {
assert_eq!(
err.to_string(),
format!("error parsing year: {}", inner.to_string())
);
} else {
unreachable!();
};
}
#[test]
fn test_parse_float() {
let res = "Manila,2001,bar".parse::<Climate>();
assert!(matches!(res, Err(ParseClimateError::ParseFloat(_))));
let err = res.unwrap_err();
if let ParseClimateError::ParseFloat(ref inner) = err {
assert_eq!(
err.to_string(),
format!("error parsing temperature: {}", inner.to_string())
);
} else {
unreachable!();
};
}
#[test]
fn test_parse_good() {
let res = "Munich,2015,23.1".parse::<Climate>();
assert_eq!(
res,
Ok(Climate {
city: "Munich".to_string(),
year: 2015,
temp: 23.1,
})
);
}
#[test]
#[ignore]
fn test_downcast() {
let res = "São Paulo,-21,28.5".parse::<Climate>();
assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
let err = res.unwrap_err();
let inner: Option<&(dyn Error + 'static)> = err.source();
assert!(inner.is_some());
assert!(inner.unwrap().is::<ParseIntError>());
}
}

56
exercises/conversions/from_str.rs
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@ -1,16 +1,31 @@
// This does practically the same thing that TryFrom<&str> does.
// from_str.rs
// This is similar to from_into.rs, but this time we'll implement `FromStr`
// and return errors instead of falling back to a default value.
// Additionally, upon implementing FromStr, you can use the `parse` method
// on strings to generate an object of the implementor type.
// You can read more about it at https://doc.rust-lang.org/std/str/trait.FromStr.html
use std::error;
use std::num::ParseIntError;
use std::str::FromStr;
#[derive(Debug)]
#[derive(Debug, PartialEq)]
struct Person {
name: String,
age: usize,
}
// We will use this error type for the `FromStr` implementation.
#[derive(Debug, PartialEq)]
enum ParsePersonError {
// Empty input string
Empty,
// Incorrect number of fields
BadLen,
// Empty name field
NoName,
// Wrapped error from parse::<usize>()
ParseInt(ParseIntError),
}
// I AM NOT DONE
// Steps:
@ -24,7 +39,7 @@ struct Person {
// If everything goes well, then return a Result of a Person object
impl FromStr for Person {
type Err = Box<dyn error::Error>;
type Err = ParsePersonError;
fn from_str(s: &str) -> Result<Person, Self::Err> {
}
}
@ -40,7 +55,7 @@ mod tests {
#[test]
fn empty_input() {
assert!("".parse::<Person>().is_err());
assert_eq!("".parse::<Person>(), Err(ParsePersonError::Empty));
}
#[test]
fn good_input() {
@ -52,41 +67,56 @@ mod tests {
}
#[test]
fn missing_age() {
assert!("John,".parse::<Person>().is_err());
assert!(matches!(
"John,".parse::<Person>(),
Err(ParsePersonError::ParseInt(_))
));
}
#[test]
fn invalid_age() {
assert!("John,twenty".parse::<Person>().is_err());
assert!(matches!(
"John,twenty".parse::<Person>(),
Err(ParsePersonError::ParseInt(_))
));
}
#[test]
fn missing_comma_and_age() {
assert!("John".parse::<Person>().is_err());
assert_eq!("John".parse::<Person>(), Err(ParsePersonError::BadLen));
}
#[test]
fn missing_name() {
assert!(",1".parse::<Person>().is_err());
assert_eq!(",1".parse::<Person>(), Err(ParsePersonError::NoName));
}
#[test]
fn missing_name_and_age() {
assert!(",".parse::<Person>().is_err());
assert!(matches!(
",".parse::<Person>(),
Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
));
}
#[test]
fn missing_name_and_invalid_age() {
assert!(",one".parse::<Person>().is_err());
assert!(matches!(
",one".parse::<Person>(),
Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
));
}
#[test]
fn trailing_comma() {
assert!("John,32,".parse::<Person>().is_err());
assert_eq!("John,32,".parse::<Person>(), Err(ParsePersonError::BadLen));
}
#[test]
fn trailing_comma_and_some_string() {
assert!("John,32,man".parse::<Person>().is_err());
assert_eq!(
"John,32,man".parse::<Person>(),
Err(ParsePersonError::BadLen)
);
}
}

74
exercises/conversions/try_from_into.rs
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@ -1,9 +1,9 @@
// try_from_into.rs
// TryFrom is a simple and safe type conversion that may fail in a controlled way under some circumstances.
// Basically, this is the same as From. The main difference is that this should return a Result type
// instead of the target type itself.
// You can read more about it at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
use std::convert::{TryFrom, TryInto};
use std::error;
#[derive(Debug, PartialEq)]
struct Color {
@ -12,12 +12,21 @@ struct Color {
blue: u8,
}
// We will use this error type for these `TryFrom` conversions.
#[derive(Debug, PartialEq)]
enum IntoColorError {
// Incorrect length of slice
BadLen,
// Integer conversion error
IntConversion,
}
// I AM NOT DONE
// Your task is to complete this implementation
// and return an Ok result of inner type Color.
// You need to create an implementation for a tuple of three integers,
// an array of three integers and a slice of integers.
// an array of three integers, and a slice of integers.
//
// Note that the implementation for tuple and array will be checked at compile time,
// but the slice implementation needs to check the slice length!
@ -25,20 +34,23 @@ struct Color {
// Tuple implementation
impl TryFrom<(i16, i16, i16)> for Color {
type Error = Box<dyn error::Error>;
fn try_from(tuple: (i16, i16, i16)) -> Result<Self, Self::Error> {}
type Error = IntoColorError;
fn try_from(tuple: (i16, i16, i16)) -> Result<Self, Self::Error> {
}
}
// Array implementation
impl TryFrom<[i16; 3]> for Color {
type Error = Box<dyn error::Error>;
fn try_from(arr: [i16; 3]) -> Result<Self, Self::Error> {}
type Error = IntoColorError;
fn try_from(arr: [i16; 3]) -> Result<Self, Self::Error> {
}
}
// Slice implementation
impl TryFrom<&[i16]> for Color {
type Error = Box<dyn error::Error>;
fn try_from(slice: &[i16]) -> Result<Self, Self::Error> {}
type Error = IntoColorError;
fn try_from(slice: &[i16]) -> Result<Self, Self::Error> {
}
}
fn main() {
@ -46,15 +58,15 @@ fn main() {
let c1 = Color::try_from((183, 65, 14));
println!("{:?}", c1);
// Since From is implemented for Color, we should be able to use Into
// Since TryFrom is implemented for Color, we should be able to use TryInto
let c2: Result<Color, _> = [183, 65, 14].try_into();
println!("{:?}", c2);
let v = vec![183, 65, 14];
// With slice we should use `from` function
// With slice we should use `try_from` function
let c3 = Color::try_from(&v[..]);
println!("{:?}", c3);
// or take slice within round brackets and use Into
// or take slice within round brackets and use TryInto
let c4: Result<Color, _> = (&v[..]).try_into();
println!("{:?}", c4);
}
@ -65,15 +77,24 @@ mod tests {
#[test]
fn test_tuple_out_of_range_positive() {
assert!(Color::try_from((256, 1000, 10000)).is_err());
assert_eq!(
Color::try_from((256, 1000, 10000)),
Err(IntoColorError::IntConversion)
);
}
#[test]
fn test_tuple_out_of_range_negative() {
assert!(Color::try_from((-1, -10, -256)).is_err());
assert_eq!(
Color::try_from((-1, -10, -256)),
Err(IntoColorError::IntConversion)
);
}
#[test]
fn test_tuple_sum() {
assert!(Color::try_from((-1, 255, 255)).is_err());
assert_eq!(
Color::try_from((-1, 255, 255)),
Err(IntoColorError::IntConversion)
);
}
#[test]
fn test_tuple_correct() {
@ -91,17 +112,17 @@ mod tests {
#[test]
fn test_array_out_of_range_positive() {
let c: Result<Color, _> = [1000, 10000, 256].try_into();
assert!(c.is_err());
assert_eq!(c, Err(IntoColorError::IntConversion));
}
#[test]
fn test_array_out_of_range_negative() {
let c: Result<Color, _> = [-10, -256, -1].try_into();
assert!(c.is_err());
assert_eq!(c, Err(IntoColorError::IntConversion));
}
#[test]
fn test_array_sum() {
let c: Result<Color, _> = [-1, 255, 255].try_into();
assert!(c.is_err());
assert_eq!(c, Err(IntoColorError::IntConversion));
}
#[test]
fn test_array_correct() {
@ -119,17 +140,26 @@ mod tests {
#[test]
fn test_slice_out_of_range_positive() {
let arr = [10000, 256, 1000];
assert!(Color::try_from(&arr[..]).is_err());
assert_eq!(
Color::try_from(&arr[..]),
Err(IntoColorError::IntConversion)
);
}
#[test]
fn test_slice_out_of_range_negative() {
let arr = [-256, -1, -10];
assert!(Color::try_from(&arr[..]).is_err());
assert_eq!(
Color::try_from(&arr[..]),
Err(IntoColorError::IntConversion)
);
}
#[test]
fn test_slice_sum() {
let arr = [-1, 255, 255];
assert!(Color::try_from(&arr[..]).is_err());
assert_eq!(
Color::try_from(&arr[..]),
Err(IntoColorError::IntConversion)
);
}
#[test]
fn test_slice_correct() {
@ -148,11 +178,11 @@ mod tests {
#[test]
fn test_slice_excess_length() {
let v = vec![0, 0, 0, 0];
assert!(Color::try_from(&v[..]).is_err());
assert_eq!(Color::try_from(&v[..]), Err(IntoColorError::BadLen));
}
#[test]
fn test_slice_insufficient_length() {
let v = vec![0, 0];
assert!(Color::try_from(&v[..]).is_err());
assert_eq!(Color::try_from(&v[..]), Err(IntoColorError::BadLen));
}
}

95
info.toml
View File

@ -941,6 +941,27 @@ mode = "test"
hint = """
Follow the steps provided right before the `From` implementation"""
[[exercises]]
name = "from_str"
path = "exercises/conversions/from_str.rs"
mode = "test"
hint = """
The implementation of FromStr should return an Ok with a Person object,
or an Err with an error if the string is not valid.
This is almost like the `from_into` exercise, but returning errors instead
of falling back to a default value.
Hint: Look at the test cases to see which error variants to return.
Another hint: You can use the `map_err` method of `Result` with a function
or a closure to wrap the error from `parse::<usize>`.
Yet another hint: If you would like to propagate errors by using the `?`
operator in your solution, you might want to look at
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reenter_question_mark.html
"""
[[exercises]]
name = "try_from_into"
path = "exercises/conversions/try_from_into.rs"
@ -949,17 +970,19 @@ hint = """
Follow the steps provided right before the `TryFrom` implementation.
You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
You might want to look back at the exercise errors5 (or its hints) to remind
yourself about how `Box<dyn Error>` works.
Hint: Is there an implementation of `TryFrom` in the standard library that
can both do the required integer conversion and check the range of the input?
If you're trying to return a string as an error, note that neither `str`
nor `String` implements `error::Error`. However, there is an implementation
of `From<&str>` for `Box<dyn Error>`. This means you can use `.into()` or
the `?` operator to convert your string into the correct error type.
Another hint: Look at the test cases to see which error variants to return.
If you're having trouble with using the `?` operator to convert an error string,
recall that `?` works to convert `Err(something)` into the appropriate error
type for returning from the function."""
Yet another hint: You can use the `map_err` or `or` methods of `Result` to
convert errors.
Yet another hint: If you would like to propagate errors by using the `?`
operator in your solution, you might want to look at
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reenter_question_mark.html
Challenge: Can you make the `TryFrom` implementations generic over many integer types?"""
[[exercises]]
name = "as_ref_mut"
@ -968,14 +991,54 @@ mode = "test"
hint = """
Add AsRef<str> as a trait bound to the functions."""
# ADVANCED ERRORS
[[exercises]]
name = "from_str"
path = "exercises/conversions/from_str.rs"
name = "advanced_errs1"
path = "exercises/advanced_errors/advanced_errs1.rs"
mode = "test"
hint = """
The implementation of FromStr should return an Ok with a Person object,
or an Err with an error if the string is not valid.
This is almost like the `try_from_into` exercise.
This exercise uses an updated version of the code in errors6. The parsing
code is now in an implementation of the `FromStr` trait. Note that the
parsing code uses `?` directly, without any calls to `map_err()`. There is
one partial implementation of the `From` trait example that you should
complete.
If you're having trouble with returning the correct error type, see the
hints for try_from_into."""
Details: The `?` operator calls `From::from()` on the error type to convert
it to the error type of the return type of the surrounding function.
Hint: You will need to write another implementation of `From` that has a
different input type.
"""
[[exercises]]
name = "advanced_errs2"
path = "exercises/advanced_errors/advanced_errs2.rs"
mode = "test"
hint = """
This exercise demonstrates a few traits that are useful for custom error
types to implement. These traits make it easier for other code to consume
the custom error type.
Follow the steps in the comment near the top of the file. You will have to
supply a missing trait implementation, and complete a few incomplete ones.
You may find these pages to be helpful references:
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/define_error_type.html
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/boxing_errors.html
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/wrap_error.html
Hint: What trait must our error type have for `main()` to return the return
type that it returns?
Another hint: It's not necessary to implement any methods inside the missing
trait. (Some methods have default implementations that are supplied by the
trait.)
Another hint: Consult the tests to determine which error variants (and which
error message text) to produce for certain error conditions.
Challenge: There is one test that is marked `#[ignore]`. Can you supply the
missing code that will make it pass? You may want to consult the standard
library documentation for a certain trait for more hints.
"""