peckr

Rust pointer type that allows packing additional data along with the underlying memory offset.

lib.rs:

Pointer type that allows packing additional data along with the underlying memory offset.

Example usage

To demonstrate the usage of this crate, we shall define an EitherBox abstraction that does not require additional storage to keep track of its variant, other than one bit that is stored inline with the memory offset of the packed pointer.

use std::mem::ManuallyDrop;

use peckr::PackedBox;

union EitherUnion<L, R> {
    left: ManuallyDrop<L>,
    right: ManuallyDrop<R>,
}

struct EitherBox<L, R> {
    inner: PackedBox<1, EitherUnion<L, R>>,
}

enum Either<L, R> {
    Left(L),
    Right(R),
}

impl<L, R> EitherBox<L, R> {
    fn left(value: L) -> Self {
        let inner = PackedBox::new(EitherUnion {
            left: ManuallyDrop::new(value),
        })
        .unwrap();
        Self { inner }
    }

    fn right(value: R) -> Self {
        let mut inner = PackedBox::new(EitherUnion {
            right: ManuallyDrop::new(value),
        })
        .unwrap();
        inner.set_bit_high(0);
        Self { inner }
    }

    fn get_ref(&self) -> Either<&L, &R> {
        match self.inner.get_bit(0) {
            false => Either::Left(unsafe { &self.inner.left }),
            true => Either::Right(unsafe { &self.inner.right }),
        }
    }
}