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Merge pull request #2047 from UnHumbleBen/patch-5
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Subtle fix to introduce ? on Option in Chapter 9.2
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steveklabnik authored Oct 14, 2019
2 parents 34b4038 + 239d99f commit aa339f7
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11 changes: 6 additions & 5 deletions src/ch09-02-recoverable-errors-with-result.md
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Expand Up @@ -470,13 +470,13 @@ and returns it. Of course, using `fs::read_to_string` doesn’t give us the
opportunity to explain all the error handling, so we did it the longer way
first.

#### The `?` Operator Can Only Be Used in Functions That Return `Result`
#### The `?` Operator Can Be Used in Functions That Return `Result`

The `?` operator can only be used in functions that have a return type of
The `?` operator can be used in functions that have a return type of
`Result`, because it is defined to work in the same way as the `match`
expression we defined in Listing 9-6. The part of the `match` that requires a
return type of `Result` is `return Err(e)`, so the return type of the function
must be a `Result` to be compatible with this `return`.
can be a `Result` to be compatible with this `return`.

Let’s look at what happens if we use the `?` operator in the `main` function,
which you’ll recall has a return type of `()`:
Expand Down Expand Up @@ -505,8 +505,9 @@ error[E0277]: the `?` operator can only be used in a function that returns
```

This error points out that we’re only allowed to use the `?` operator in a
function that returns `Result<T, E>`. When you’re writing code in a function
that doesn’t return `Result<T, E>`, and you want to use `?` when you call other
function that returns `Result` or `Option` or another type that implements
`std::ops::Try`. When you’re writing code in a function
that doesn’t return one of these types, and you want to use `?` when you call other
functions that return `Result<T, E>`, you have two choices to fix this problem.
One technique is to change the return type of your function to be `Result<T,
E>` if you have no restrictions preventing that. The other technique is to use
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