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doc: Add another restriction to the list of ownership rules.

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nham 2014-08-27 20:02:59 -04:00
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src/doc/guide.md
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@ -3668,15 +3668,20 @@ because it's easy. And if you need precise control over when something is
deallocated, leaving it up to your runtime can make this difficult.
Rust chooses a different path, and that path is called **ownership**. Any
binding that creates a resource is the **owner** of that resource. Being an
owner gives you three privileges, with two restrictions:
binding that creates a resource is the **owner** of that resource.
Being an owner affords you some privileges:
1. You control when that resource is deallocated.
2. You may lend that resource, immutably, to as many borrowers as you'd like.
3. You may lend that resource, mutably, to a single borrower. **BUT**
4. Once you've done so, you may not also lend it out otherwise, mutably or
immutably.
5. You may not lend it out mutably if you're currently lending it to someone.
3. You may lend that resource, mutably, to a single borrower.
But it also comes with some restrictions:
1. If someone is borrowing your resource (either mutably or immutably), you may
not mutate the resource or mutably lend it to someone.
2. If someone is mutably borrowing your resource, you may not lend it out at
all (mutably or immutably) or access it in any way.
What's up with all this 'lending' and 'borrowing'? When you allocate memory,
you get a pointer to that memory. This pointer allows you to manipulate said