I think the situation is a little confusing at the moment with a lack of `Index` traits. The slice method [`get`](http://doc.rust-lang.org/std/slice/trait.ImmutableVector.html#tymethod.get) returns an `Option<&T>`, and apparently `get_mut` doesn't exist on slices?!

For `Vec`, `get` and `get_mut` return `&T` and `&mut T`, but I believe this is a stopgap until the indexing traits are available, and then I think they should return the same thing as slices.

So basically we have two conventions, but I'd be more in favor of `get` and `get_mut` returning `Option` and then implementing the `Index` traits when they exist for tuples as well (failing if out of bounds).