diff options
Diffstat (limited to 'error_handling/errorsn.rs')
| -rw-r--r-- | error_handling/errorsn.rs | 32 |
1 files changed, 25 insertions, 7 deletions
diff --git a/error_handling/errorsn.rs b/error_handling/errorsn.rs index 4b0d56e..e0d73da 100644 --- a/error_handling/errorsn.rs +++ b/error_handling/errorsn.rs @@ -1,4 +1,5 @@ // 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 // 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(); b.read_line(&mut line); 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. @@ -59,6 +61,7 @@ fn test_ioerror() { } let mut b = io::BufReader::new(Broken); assert!(read_and_validate(&mut b).is_err()); + assert_eq!("uh-oh!", read_and_validate(&mut b).unwrap_err().to_string()); } #[derive(PartialEq,Debug)] @@ -109,11 +112,26 @@ impl error::Error for CreationError { // `read_and_validate` returns and`test_with_str` has its signature fully // specified. -// Next hint: anywhere in `read_and_validate` that we call a function that -// returns a `Result`, wrap that call in a `try!` macro call. Use the compiler -// error messages and warnings to guide you to all the places you need to do -// this. You might need to rewrap some `try!` return values in a `Result::Ok`! +// Next hint: There are three places in `read_and_validate` that we call a +// function that returns a `Result` (that is, the functions might fail). +// Wrap those calls in a `try!` macro call so that we return immediately from +// `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>, -// 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 |