func (is IdentifierSlice) Swap(i, j int) {
	is[i], is[j] = is[j], is[i]
}
func (is IdentifierSlice) Swap(i, j int) {
	is[i], is[j] = is[j], is[i]
}
func ( is IdentifierSlice ) Swap ( i , j int ) { is [ i ] , is [ j ] = is [ j ] , is [ i ] }
// Swap the elements at positions i and j
// part of the sort.Interface
Swap the elements at positions i and j part of the sort . Interface