One-liner to transform []int into string

You can always json.Marshal:

data := []int{1,2,3}
s, _ := json.Marshal(data)
fmt.Println(string(s))
// output: [1, 2, 3]

fmt.Println(strings.Trim(string(s), "[]"))
//output 1,2,3

I've just run into the same problem today, since I've not found anything on standard library, I've recompiled 3 ways to do this conversion

Create a string and appending the values from the array by converting it using strconv.Itoa:

func IntToString1() string {
    a := []int{1, 2, 3, 4, 5}
    b := ""
    for _, v := range a {
        if len(b) > 0 {
            b += ","
        }
        b += strconv.Itoa(v)
    }

    return b
}

Create a []string, convert each array value and then return a joined string from []string:

func IntToString2() string {
    a := []int{1, 2, 3, 4, 5}
    b := make([]string, len(a))
    for i, v := range a {
        b[i] = strconv.Itoa(v)
    }

    return strings.Join(b, ",")
}

Convert the []int to a string and replace / trim the value:

func IntToString3() string {
    a := []int{1, 2, 3, 4, 5}
    return strings.Trim(strings.Replace(fmt.Sprint(a), " ", ",", -1), "[]")
}

Performance is quite different depending on implementation:

BenchmarkIntToString1-12         3000000           539 ns/op
BenchmarkIntToString2-12         5000000           359 ns/op
BenchmarkIntToString3-12         1000000          1162 ns/op

Personally, I'll go with IntToString2, so the final function could be an util package in my project like this:

func SplitToString(a []int, sep string) string {
    if len(a) == 0 {
        return ""
    }

    b := make([]string, len(a))
    for i, v := range a {
        b[i] = strconv.Itoa(v)
    }
    return strings.Join(b, sep)
}

To convert
A := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}

to a one line delimited string like
"1,2,3,4,5,6,7,8,9"
use:

strings.Trim(strings.Join(strings.Fields(fmt.Sprint(A)), delim), "[]")

or:

strings.Trim(strings.Join(strings.Split(fmt.Sprint(A), " "), delim), "[]")

or:

strings.Trim(strings.Replace(fmt.Sprint(A), " ", delim, -1), "[]")

and return it from a function such as in this example:

package main

import "fmt"
import "strings"

func arrayToString(a []int, delim string) string {
    return strings.Trim(strings.Replace(fmt.Sprint(a), " ", delim, -1), "[]")
    //return strings.Trim(strings.Join(strings.Split(fmt.Sprint(a), " "), delim), "[]")
    //return strings.Trim(strings.Join(strings.Fields(fmt.Sprint(a)), delim), "[]")
}

func main() {
    A := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}

    fmt.Println(arrayToString(A, ",")) //1,2,3,4,5,6,7,8,9
}

To include a space after the comma you could call arrayToString(A, ", ") or conversely define the return as return strings.Trim(strings.Replace(fmt.Sprint(a), " ", delim + " ", -1), "[]") to force its insertion after the delimiter.