To my understanding, currently, a reference type has only one niche that is the null value, but a reference type must be properly aligned, which means in theory we can also utilize those unaligned values as niches. The total possible niches of a type can be calculated as:
fn reference_niches<T>() -> usize {
((MEMORY_SPACE_SIZE - size_of::<T>()) / align_of::<T>()).wrapping_neg()
}where MEMORY_SPACE_SIZE is the theoretical maximum size of the memory space in bytes.
Is it possible for Rust to enable this optimization?
Additionally, is it possible to add a new NonNullAligned<T> type that has the same niches as &T? We can use it to implement Box, Rc, Arc and Vec types, so they can also have the same niches.
To my understanding, currently, a reference type has only one niche that is the null value, but a reference type must be properly aligned, which means in theory we can also utilize those unaligned values as niches. The total possible niches of a type can be calculated as:
where
MEMORY_SPACE_SIZEis the theoretical maximum size of the memory space in bytes.Is it possible for Rust to enable this optimization?
Additionally, is it possible to add a new
NonNullAligned<T>type that has the same niches as&T? We can use it to implementBox,Rc,ArcandVectypes, so they can also have the same niches.