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Diffstat (limited to 'info.toml')
| -rw-r--r-- | info.toml | 61 |
1 files changed, 34 insertions, 27 deletions
@@ -499,42 +499,49 @@ It should be doing some checking, returning an `Err` result if those checks fail returning an `Ok` result if those checks determine that everything is... okay :)""" [[exercises]] -name = "errorsn" -path = "exercises/error_handling/errorsn.rs" -mode = "test" +name = "errors5" +path = "exercises/error_handling/errors5.rs" +mode = "compile" hint = """ -First hint: To figure out what type should go where the ??? is, take a look -at the test helper function `test_with_str`, since it returns whatever -`read_and_validate` returns and `test_with_str` has its signature fully -specified. - - -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). -Apply the `?` operator on those calls so that we return immediately from -`read_and_validate` if those function calls fail. - +Hint: There are two different possible `Result` types produced within +`main()`, which are propagated using `?` operators. How do we declare a +return type from `main()` that allows both? Another hint: under the hood, the `?` operator calls `From::from` -on the error value to convert it to a boxed trait object, a Box<dyn error::Error>, -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. +on the error value to convert it to a boxed trait object, a +`Box<dyn error::Error>`, 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/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator +This exercise uses some concepts that we won't get to until later in the +course, like `Box` and the `From` trait. It's not important to understand +them in detail right now, but you can read ahead if you like. + +Read more about boxing errors: +https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/boxing_errors.html -Another another hint: Note that because the `?` operator 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 `?`ed call in an `Ok`-- this will -look like `Ok(something)`. +Read more about using the `?` operator with boxed errors: +https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reenter_question_mark.html +""" + +[[exercises]] +name = "errors6" +path = "exercises/error_handling/errors6.rs" +mode = "test" +hint = """ +This exercise uses a completed version of `PositiveNonzeroInteger` from +the errors4. +Below the TODO line, there is an example of using the `.or()` method +on a `Result` to transform one type of error into another. Try using +something similar on the `Result` from `parse()`. You might use the `?` +operator to return early from the function, or you might use a `match` +expression, or maybe there's another way! -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""" +Read more about `.or()` in the `std::result` documentation: +https://doc.rust-lang.org/std/result/enum.Result.html#method.or""" # Generics |