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# References
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There are two kinds of reference:
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* Shared reference: `&`
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* Mutable reference: `&mut`
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Which obey the following rules:
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* A reference cannot outlive its referent
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* A mutable reference cannot be aliased
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That's it. That's the whole model references follow.
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Of course, we should probably define what *aliased* means.
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```text
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error[E0425]: cannot find value `aliased` in this scope
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--> <rust.rs>:2:20
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2 | println!("{}", aliased);
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| ^^^^^^^ not found in this scope
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error: aborting due to previous error
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```
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Unfortunately, Rust hasn't actually defined its aliasing model. 🙀
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While we wait for the Rust devs to specify the semantics of their language,
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let's use the next section to discuss what aliasing is in general, and why it
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matters.
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