golang sort slice ascending or descending

I need to sort a slice of a type that is coming from a 3rd party package. Based on some condition the order must be ascending or descending.

The solution I come up with is:

type fooAscending []foo

func (v fooAscending) Len() int           { return len(v) }
func (v fooAscending) Swap(i, j int)      { v[i], v[j] = v[j], v[i] }
func (v fooAscending) Less(i, j int) bool { return v[i].Amount  v[j].Amount }

if someCondition {
    sort.Sort(fooAscending(array))
} else {
    sort.Sort(fooDescending(array))
}

Is there a better way to do this. 13 lines of code for this task and most of it is duplicated, seems a bit too much.

As of Go 1.8, there is an easier way to sort a slice that does not require you to define new types. You simply pass an anonymous function to the sort.Slice function.

a := []int{5, 3, 4, 7, 8, 9}
sort.Slice(a, func(i, j int) bool {
    return a[i] < a[j]
})
for _, v := range a {
    fmt.Println(v)
}

This will sort in ascending order, if you want the opposite, simply write a[i] > a[j] in the anonymous function.

Stack Overflow Q#37695209, score: 218