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Make note that this is different in std #31295

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Jan 30, 2016
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Make note that this is different in std #31295

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5 changes: 5 additions & 0 deletions src/doc/book/error-handling.md
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Expand Up @@ -265,6 +265,8 @@ fn map<F, T, A>(option: Option<T>, f: F) -> Option<A> where F: FnOnce(T) -> A {
```

Indeed, `map` is [defined as a method][2] on `Option<T>` in the standard library.
As a method, it has a slighly different signature: methods take `self`, `&self`,
or `&mut self` as their first argument.

Armed with our new combinator, we can rewrite our `extension_explicit` method
to get rid of the case analysis:
Expand Down Expand Up @@ -294,6 +296,9 @@ fn unwrap_or<T>(option: Option<T>, default: T) -> T {
}
```

Like with `map` above, the standard library implementation is a method instead
of a free function.

The trick here is that the default value must have the same type as the value
that might be inside the `Option<T>`. Using it is dead simple in our case:

Expand Down