sort.Search <https://pkg.go.dev/sort#Search> is a binary chop, and needs an
ordering condition, >= or <=. If you use == then it cannot work.
In addition you're getting a panic here:
if ret < len(haystack) {
index += ret
log.Println("found", index, haystack[index])
}
by letting index increment past the end of the slice.
On Tuesday, 11 October 2022 at 13:22:29 UTC+1 ljh wrote:
> Hi community,
>
> I used sort.Search on a sorted slice in below code started at Line 36, and
> it worked.
>
> I also tried to call sort.Search in a loop, started at Line 53. It does
> not seem to work. How can I correct the loop version?
>
> Thanks
>
> ---
>
> package main
>
> import (
> "log"
> "sort"
> )
>
> type T struct {
> name string
> }
>
> func main() {
> log.SetFlags(log.LstdFlags | log.Llongfile)
>
> haystack := []T{
> // {name: "apple", },
> {name: "compote", }, //dup
> {name: "orange", },
> {name: "compote", }, //dup
> }
>
> sort.Slice(haystack, func(i, j int) bool {
> if haystack[i].name < haystack[j].name {
> return true
> } else {
> return false
> }
> })
>
> for _, t := range haystack {
> log.Println("sorted", t)
> }
>
> needle := T{name: "compote"}
>
> // Style 1: ok, lower upper bounds style // Line 36
> /*
> lower := sort.Search(len(haystack), func(i int) bool {
> return haystack[i].name == needle.name
> })
>
> upper := sort.Search(len(haystack), func(i int) bool {
> return haystack[i].name > needle.name
> })
>
> if lower != len(haystack) {
> for i := lower; i != upper; i++ {
> log.Println("found", i, haystack[i])
> }
> }
> */
>
> // Style 2: error, loop style // Line 53
> for index := 0; index < len(haystack); index++ {
> ret := sort.Search(len(haystack[index:]), func(i int) bool {
> return haystack[index:][i].name == needle.name })
>
> log.Println(index, ret)
>
> if ret < len(haystack) {
> index += ret
> log.Println("found", index, haystack[index])
> }
> }
> }
>
>
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