There are two main tasks that `betteralign` does:

1. Create a candidate layout order by sorting fields by **descending alignment** required (reducing holes/padding between struct fields),

2. Reduce **pointer bytes scanned** by GC ([GC will stop scanning values](https://go.dev/doc/gc-guide) at the last pointer in the value).

So having in mind those two tasks, field sort is performed the following way:

1. **Zero sized** objects are placed before non-zero sized objects,

2. More **tightly aligned** objects are placed before less tightly aligned objects,

3. **Pointerful objects** are placed before pointer-free objects,

4. If both objects have pointers, objects with less **trailing non-pointer objects** are placed earlier,

5. Lastly, order by **size**.

In case of the following:

package foo

type IPAddr struct {

Zone string // 16 bytes, 8-byte aligned

IP []byte // 24 bytes, 8-byte aligned

}

Reason why `Zone` gets to be the first field is because trailing data comparison: `Sizeof(string) - ptrdata(string) = 8` vs `Sizeof([]byte) - ptrdata([]byte) = 16`, causing `string` field type to go first in struct `IPAddr` having less trailing non-pointer data.