Golang remove dup ints from slice append function "evaluated but not used"

Question

I can't get this Go lang test program to run. The compiler keeps giving an error on the append() function call below with an "evaluated but not used" error. I can't figure out why.

package main

import (
    "fmt"
)

func removeDuplicates(testArr *[]int) int {

    prevValue := (*testArr)[0]
    for curIndex := 1; curIndex < len((*testArr)); curIndex++ {
        curValue := (*testArr)[curIndex]
        if curValue == prevValue {
            append((*testArr)[:curIndex], (*testArr)[curIndex+1:]...)
        }
        prevValue = curValue
    }
    return len(*testArr)
}

func main() {
    testArr := []int{0, 0, 1, 1, 1, 2, 2, 3, 3, 4}

    nonDupSize := removeDuplicates(&testArr)

    fmt.Printf("nonDupSize = %d", nonDupSize)
}

Well, because you're not using the return value of append. Append may return a new slice, so you have to assign the return value. https://tour.golang.org/moretypes/15 — Peter, Oct 13 '18 at 20:51
Yep, that fixed the compile error, next question is this going to allocate a new slice? — gtalton007, Oct 13 '18 at 21:06
The [append documentation](https://godoc.org/builtin#append) answers your next question. — Charlie Tumahai, Oct 13 '18 at 22:48
See also https://blog.golang.org/go-slices-usage-and-internals — Peter, Oct 14 '18 at 08:45

score 0 · Accepted Answer · answered Oct 17 '18 at 04:15

"evaluated but not used" error.

Code below is my idea. I think your code is not very clear.

package main

import (
    "fmt"
)

func removeDuplicates(testArr *[]int) int {
    m := make(map[int]bool)
    arr := make([]int, 0)

    for curIndex := 0; curIndex < len((*testArr)); curIndex++ {
        curValue := (*testArr)[curIndex]
        if has :=m[curValue]; !has {
            m[curValue] = true
            arr = append(arr, curValue)
        }
    }
    *testArr = arr
    return len(*testArr)
}

func main() {
    testArr := []int{0, 0, 1, 1, 1, 2, 2, 3, 3, 4}

    nonDupSize := removeDuplicates(&testArr)

    fmt.Printf("nonDupSize = %d", nonDupSize)
}

score 0 · Answer 2 · answered Oct 18 '18 at 11:20

0

Peter's answer nailed it, the compile error was due to not grabbing the return value from append()

answered Oct 18 '18 at 11:20

gtalton007

21
3

Golang remove dup ints from slice append function "evaluated but not used"

2 Answers2