mirror of https://github.com/rust-lang/rustlings
feature: improve error_handling exercises
Add new exercises errors5 and errors6, to introduce boxed errors and custom error enums more gently. Delete errorsn, because it tried to do too much too soon.pull/772/head
Taylor Yu
3 years ago
parent
50ab289da6
commit
68d3ac567c
@ -0,0 +1,53 @@
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// errors5.rs
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// This program uses a completed version of the code from errors4.
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// It won't compile right now! Why?
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// Execute `rustlings hint errors5` for hints!
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// I AM NOT DONE
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use std::error;
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use std::fmt;
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use std::num::ParseIntError;
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// TODO: update the return type of `main()` to make this compile.
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fn main() -> Result<(), ParseIntError> {
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let pretend_user_input = "42";
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let x: i64 = pretend_user_input.parse()?;
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println!("output={:?}", PositiveNonzeroInteger::new(x)?);
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Ok(())
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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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// This is required so that `CreationError` can implement `error::Error`.
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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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let description = match *self {
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CreationError::Negative => "Number is negative",
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CreationError::Zero => "Number is zero",
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};
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f.write_str(description)
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}
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}
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impl error::Error for CreationError {}
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@ -0,0 +1,86 @@
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// 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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// 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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CreationError,
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ParseIntError
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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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.or(Err(ParsePosNonzeroError::CreationError))
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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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assert_eq!(
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parse_pos_nonzero("not a number"),
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Err(ParsePosNonzeroError::ParseIntError)
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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::CreationError)
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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::CreationError)
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);
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}
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#[test]
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fn test_positive() {
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assert_eq!(
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parse_pos_nonzero("42"),
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Ok(PositiveNonzeroInteger(42))
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);
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}
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}
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@ -1,117 +0,0 @@
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// errorsn.rs
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// This is a bigger error exercise than the previous ones!
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// You can do it! :)
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//
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// Edit the `read_and_validate` function ONLY. Don't create any Errors
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// that do not already exist.
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//
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// So many things could go wrong!
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//
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// - Reading from stdin could produce an io::Error
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// - Parsing the input could produce a num::ParseIntError
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// - Validating the input could produce a CreationError (defined below)
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//
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// How can we lump these errors into one general error? That is, what
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// type goes where the question marks are, and how do we return
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// that type from the body of read_and_validate?
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//
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// Execute `rustlings hint errorsn` for hints :)
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// I AM NOT DONE
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use std::error;
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use std::fmt;
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use std::io;
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// PositiveNonzeroInteger is a struct defined below the tests.
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fn read_and_validate(b: &mut dyn io::BufRead) -> Result<PositiveNonzeroInteger, ???> {
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let mut line = String::new();
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b.read_line(&mut line);
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let num: i64 = line.trim().parse();
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let answer = PositiveNonzeroInteger::new(num);
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answer
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}
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//
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// Nothing below this needs to be modified
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//
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// This is a test helper function that turns a &str into a BufReader.
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fn test_with_str(s: &str) -> Result<PositiveNonzeroInteger, Box<dyn error::Error>> {
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let mut b = io::BufReader::new(s.as_bytes());
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read_and_validate(&mut b)
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}
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#[test]
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fn test_success() {
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let x = test_with_str("42\n");
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assert_eq!(PositiveNonzeroInteger(42), x.unwrap());
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}
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#[test]
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fn test_not_num() {
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let x = test_with_str("eleven billion\n");
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assert!(x.is_err());
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}
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#[test]
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fn test_non_positive() {
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let x = test_with_str("-40\n");
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assert!(x.is_err());
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}
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#[test]
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fn test_ioerror() {
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struct Broken;
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impl io::Read for Broken {
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fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> {
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Err(io::Error::new(io::ErrorKind::BrokenPipe, "uh-oh!"))
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}
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}
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let mut b = io::BufReader::new(Broken);
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assert!(read_and_validate(&mut b).is_err());
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assert_eq!("uh-oh!", read_and_validate(&mut b).unwrap_err().to_string());
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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<PositiveNonzeroInteger, CreationError> {
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if value == 0 {
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Err(CreationError::Zero)
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} else if value < 0 {
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Err(CreationError::Negative)
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} else {
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Ok(PositiveNonzeroInteger(value as u64))
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}
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}
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}
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#[test]
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fn test_positive_nonzero_integer_creation() {
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assert!(PositiveNonzeroInteger::new(10).is_ok());
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assert_eq!(
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Err(CreationError::Negative),
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PositiveNonzeroInteger::new(-10)
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);
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assert_eq!(Err(CreationError::Zero), PositiveNonzeroInteger::new(0));
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}
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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 fmt::Display for CreationError {
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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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CreationError::Negative => "Number is negative",
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CreationError::Zero => "Number is zero",
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};
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f.write_str(description)
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}
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}
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impl error::Error for CreationError {}
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