Sorting by Fields Doesn't Always Work #2
Description
When you have a slice of pointers to structs and you sort by a field within the struct, it doesn't always work. If you add this test case to the all_test.go file and run the tests it fails.
func TestAscByFieldInt64_Pointers(t *testing.T) {
now := time.Now()
is := []*Item{
{5, "", now, false},
{2, "", now, false},
{1, "", now, false},
{4, "", now, false},
{3, "", now, false},
}
AscByField(is, "Id")
for i, v := range is {
if v.Id != int64(i+1) {
t.Errorf("is[%d].Id is not %d, but %d", i, i+1, v.Id)
}
}
}The sequence of test numbers matters. Some initial ordering of values will still work, while some will not.
I believe the issue is related to the Sorter.vals slice getting out of sync with the Sorter.Slice when swapping elements. When a swap happens on the Sorter.Slice, the pointers to the structs are properly moved, but because the Sorter.vals slice contains reflect.Value "pointing" to a field, indexing the Sorter.vals array will now give you the wrong value for the element in the slice.
The test case above will pass by adding
s.vals[i], s.vals[j] = s.vals[j], s.vals[i]to the bottom of the Sorter.Swap func. But an array of values (not pointers) will now fail.
I tried modifying the code so that the Getter would return a boolean indicating if the values needed to swapped (based on if indirection was needed), but I couldn't get all the Benchmarks to pass, and I ran out of time to continue digging into it.
I can share what I did get done, although I'm not 100% sure it is the best way to go about fixing the issue.