patterngoCritical

golang append() evaluated but not used

Submitted by: @import:stackoverflow-api·Mar 10, 2026·

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evaluatedusedgolangappendnotbut

Problem

func main(){
     var array [10]int
     sliceA := array[0:5]
     append(sliceA, 4)
     fmt.Println(sliceA)
}

Error : append(sliceA, 4) evaluated but not used

I don't Know why? The slice append operation is not run...

Solution

Refer: Appending to and copying slices

In Go, arguments are passed by value.

Typical append usage is:

a = append(a, x)

You need to write:

func main(){
    var array [10]int
    sliceA := array[0:5]
    // append(sliceA, 4)  // discard
    sliceA = append(sliceA, 4)  // keeping return value is mandatory
    fmt.Println(sliceA)
}

Output:

[0 0 0 0 0 4]

Code Snippets

a = append(a, x)

func main(){
    var array [10]int
    sliceA := array[0:5]
    // append(sliceA, 4)  // discard
    sliceA = append(sliceA, 4)  // keeping return value is mandatory
    fmt.Println(sliceA)
}

[0 0 0 0 0 4]

Context

Stack Overflow Q#45004854, score: 142

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