fn capacityInBytes(capacity: usize) usize {
    var bytes_count: usize = 0;
    for (sizes.bytes) |field_size| {
        bytes_count += capacity * field_size;
    }
    return bytes_count;
}

// Using SIMD:

fn capacityInBytes(capacity: usize) usize {
    const sizes_vector: std.meta.Vector(sizes.bytes.len, usize) = sizes.bytes;
    const capacity_vector = @splat(sizes.bytes.len, capacity);
    return @reduce(.Add, capacity_vector * sizes_vector);
}