This crate provides a type with a pre-specified size, regardless of the size of the T type it contains, using heap allocation if necessary.
The purpose of this crate is allow the size of a generic to argument to dictate where it is stored. This is useful when you want to pack the layout of structures, e.g. for optimizing memory access, but the structure contains a generic type parameter with a size that is unknown to you.
If size_of::<T>() <= size_of::<SizeT>() performance should be as close to using the raw type as possible. If size_of::<T>() > size_of::<SizeT>(), performance should be as close to a box as possible.
This crate serves a similar function to smallbox but it has slightly lower runtime overhead (memory and instructions) in exchange for not being able to handle dynamically sized types.
use local_or_heap::LocalOrHeap;
let int_obj = LocalOrHeap::<usize>::new(42);
assert_eq!(LocalOrHeap::<usize>::is_heap(), false);
assert_eq!(&*int_obj, &42);
let buf_obj = LocalOrHeap::<[usize; 8]>::new([0, 1, 2, 3, 4, 5, 6, 7]);
assert_eq!(LocalOrHeap::<[usize; 8]>::is_heap(), true);
assert_eq!(buf_obj.as_ref(), &[0, 1, 2, 3, 4, 5, 6, 7]); use local_or_heap::LocalOrHeap;
type LoH = LocalOrHeap::<[usize; 8], [u8; 1024]>;
let buf_obj = LoH::new([0, 1, 2, 3, 4, 5, 6, 7]);
assert_eq!(LoH::is_heap(), false);
assert_eq!(&*buf_obj, &[0, 1, 2, 3, 4, 5, 6, 7]);
assert_eq!(core::mem::size_of::<LoH>(), 1024);