Column Vec

colvec provides a derive macro which generates a Vec-like data structure. Compared to Vec<Example>, ExampleColVec has a transposed row / column layout. This means you can take a slice across an entire column of a single struct field. ColVec has the same struct size (size_of::<Vec<T>>() = 24 bytes) and growth factor (2) as Vec, and uses a single contiguous allocation.

Tradeoffs

• ColVec can be smaller than Vec when the Struct has padding, since no padding is needed in the transposed layout [^1].
• ColVec can be faster to iterate than Vec when only accessing a single struct field column because the unused data in the other fields do not occupy the cache line, and thus it has reduced cache eviction.

[^1]: To ensure proper alignment, the capacity is rounded up to a multiple of the item alignment.

Example

use colvec::ColVec;

#[derive(ColVec)]
struct Example{
	field1:u8,
	field2:Option<u8>,
	field3:i16,
	field4:u32,
}

let mut cols=ExampleColVec::new();
cols.push(Example{
	field1:1,
	field2:Some(2),
	field3:3,
	field4:4,
});
cols.push(Example{
	field1:5,
	field2:Some(6),
	field3:7,
	field4:8,
});

assert_eq!(&[1,5], cols.field1_slice());
assert_eq!(&[Some(2),Some(6)], cols.field2_slice());
assert_eq!(&[3,7], cols.field3_slice());
assert_eq!(&[4,8], cols.field4_slice());

License