Add more hints, better test failures, etc to errorsn

This commit is contained in:
Carol (Nichols || Goulding) 2016-06-21 11:10:21 -04:00
parent 0b15e92738
commit 4378a2c5bf
2 changed files with 26 additions and 8 deletions

File diff suppressed because one or more lines are too long

View File

@ -1,4 +1,5 @@
// This is a bigger error exercise than the previous ones! // This is a bigger error exercise than the previous ones!
// You can do it!
// //
// Edit the `read_and_validate` function so that it compiles and // Edit the `read_and_validate` function so that it compiles and
// passes the tests... so many things could go wrong! // passes the tests... so many things could go wrong!
@ -22,7 +23,8 @@ fn read_and_validate(b: &mut io::BufRead) -> Result<PositiveNonzeroInteger, ???>
let mut line = String::new(); let mut line = String::new();
b.read_line(&mut line); b.read_line(&mut line);
let num: i64 = line.trim().parse(); let num: i64 = line.trim().parse();
PositiveNonzeroInteger::new(num) let answer = PositiveNonzeroInteger::new(num);
answer
} }
// This is a test helper function that turns a &str into a BufReader. // This is a test helper function that turns a &str into a BufReader.
@ -59,6 +61,7 @@ fn test_ioerror() {
} }
let mut b = io::BufReader::new(Broken); let mut b = io::BufReader::new(Broken);
assert!(read_and_validate(&mut b).is_err()); assert!(read_and_validate(&mut b).is_err());
assert_eq!("uh-oh!", read_and_validate(&mut b).unwrap_err().to_string());
} }
#[derive(PartialEq,Debug)] #[derive(PartialEq,Debug)]
@ -109,11 +112,26 @@ impl error::Error for CreationError {
// `read_and_validate` returns and`test_with_str` has its signature fully // `read_and_validate` returns and`test_with_str` has its signature fully
// specified. // specified.
// Next hint: anywhere in `read_and_validate` that we call a function that // Next hint: There are three places in `read_and_validate` that we call a
// returns a `Result`, wrap that call in a `try!` macro call. Use the compiler // function that returns a `Result` (that is, the functions might fail).
// error messages and warnings to guide you to all the places you need to do // Wrap those calls in a `try!` macro call so that we return immediately from
// this. You might need to rewrap some `try!` return values in a `Result::Ok`! // `read_and_validate` if those function calls fail.
// This works because under the hood, the `try!` macro calls `From::from` // Another hint: under the hood, the `try!` macro calls `From::from`
// on the error value to convert it to a boxed trait object, a Box<error::Error>, // on the error value to convert it to a boxed trait object, a Box<error::Error>,
// which is polymorphic. // which is polymorphic-- that means that lots of different kinds of errors
// can be returned from the same function because all errors act the same
// since they all implement the `error::Error` trait.
// Check out this section of the book:
// https://doc.rust-lang.org/stable/book/error-handling.html#standard-library-traits-used-for-error-handling
// Another another hint: Note that because the `try!` macro returns
// the *unwrapped* value in the `Ok` case, if we want to return a `Result` from
// `read_and_validate` for *its* success case, we'll have to rewrap a value
// that we got from the return value of a `try!` call in an `Ok`-- this will
// look like `Ok(something)`.
// Another another another hint: `Result`s must be "used", that is, you'll
// get a warning if you don't handle a `Result` that you get in your
// function. Read more about that in the `std::result` module docs:
// https://doc.rust-lang.org/std/result/#results-must-be-used