@align

Add the @align(N) decorator on a struct to specify the minimum alignment in bytes. The value N must be a positive power of 2.

For example, adding @align(64) on a struct containing an Int (8-byte aligned) aligns the struct to 64 bytes:

from sys import align_of

@align(64)
struct CacheAligned:
    var data: Int

fn main():
    print(align_of[CacheAligned]())  # Prints 64

The actual alignment will be max(N, natural_alignment), because you cannot reduce alignment below the struct's natural alignment. For example, @align(1) on a struct containing an Int (8-byte aligned) will emit a warning and the struct will remain 8-byte aligned.

Both stack and heap allocations respect @align.

Parametric alignment

The alignment value can also be a struct parameter, enabling generic aligned types:

from sys import align_of

@align(Self.alignment)
struct AlignedBuffer[alignment: Int]:
    var data: Int

fn main():
    print(align_of[AlignedBuffer[64]]())   # Prints 64
    print(align_of[AlignedBuffer[128]]())  # Prints 128

The alignment is validated when the struct is instantiated, so invalid values like AlignedBuffer[3] will produce a compile-time error.

Parametric alignment​

Parametric alignment