`rebind!` macro

[CeleritasCelery]

The rebind macro has this definition:

rune/src/arena/mod.rs

Lines 96 to 102 in 7136b74

	macro_rules! rebind {
	($item:ident, $arena:ident) => {
	#[allow(unused_qualifications)]
	let bits: $crate::object::RawObj = $item.into();
	let $item = unsafe { $arena.rebind_raw_ptr(bits) };
	};
	}

We are casting the object into a raw form that removes the lifetime. Then we call an unsafe function to create a new object from that raw pointer

Why this is safe

We are not actually changing the &mut reference to Arena. Instead we are releasing it then reborrowing it immutabley. We make sure to shadow the name so the old binding is no longer available.