Is get2_unchecked_mut redundant?

[Ralith]

It's unclear to me why this should ever be preferred over calling get_unchecked twice. Can we avoid maintaining an extra interface here?

[hawkw]

get_unchecked_mut mutably borrows the Slab, so the interface doesn't permit mutably borrowing a second item while one is already borrowed. get2_unchecked_mut can be used to mutate two entries at a time (such as mem::swapping them).

[Ralith]

Fair enough!

[hawkw]

I notice the docs for get2_mut explain the use-case for it:

slab/src/lib.rs

Lines 693 to 709 in 3340fdc

	/// This function can be used to get two mutable references out of one slab,
	/// so that you can manipulate both of them at the same time, eg. swap them.
	///
	/// # Examples
	///
	/// ```
	/// # use slab::*;
	/// use std::mem;
	///
	/// let mut slab = Slab::new();
	/// let key1 = slab.insert(1);
	/// let key2 = slab.insert(2);
	/// let (value1, value2) = slab.get2_mut(key1, key2).unwrap();
	/// mem::swap(value1, value2);
	/// assert_eq!(slab[key1], 2);
	/// assert_eq!(slab[key2], 1);
	/// ```

but the docs for get2_unchecked_mut don't, really:

slab/src/lib.rs

Lines 783 to 787 in 3340fdc

	/// Return two mutable references to the values associated with the two
	/// given keys simultaneously without performing bounds checking and safety
	/// condition checking.
	///
	/// This function should be used with care.

Maybe we could make this a little clearer by having the doc comment for get2_unchecked_mut explain the intended use-case, or adding a "This is a version of [get2_mut] that doesn't perform bounds and safety condition checks" or something?