golang字符串。构建器类型未定义

I was having a problem with the strings.Builder type in GO.

Attempted to run the example code verbatim and GO still responds with:

undefined: strings.Builder

Any clues as to what the problem can be, there's been not other problems at all.

package main

import (
    "fmt"
    "strings"
)

func main() {

    var b strings.Builder
    for i := 3; i >=1; i-- {
        fmt.Fprintf(&b, "%x...", i)
    }
    b.WriteString("ignition")
    fmt.Println(b.String())
}

strings.Builder was added in Go 1.10 (released 2018-02-16, 9 days ago at the time of writing). If you are building using an older version of Go, it won't be available.

If must working with older Go version, you can use bytes.Buffer instead.