Checking a string contains only ASCII characters - go

Question

Does Go have any method or there is a suggestion how to check if a string contains only ASCII characters? What is the right way to do it?
From my research, one of the solution is to check whatever there is any char greater than 127.
func isASCII(s string) bool {
for _, c := range s {
if c > unicode.MaxASCII {
return false
}
}
return true
}

Answer 1

In Go, we care about performance, Therefore, we would benchmark your code:
func isASCII(s string) bool {
for _, c := range s {
if c > unicode.MaxASCII {
return false
}
}
return true
}
BenchmarkRange-4 20000000 82.0 ns/op
A faster (better, more idiomatic) version, which avoids unnecessary rune conversions:
func isASCII(s string) bool {
for i := 0; i < len(s); i++ {
if s[i] > unicode.MaxASCII {
return false
}
}
return true
}
BenchmarkIndex-4 30000000 55.4 ns/op
ascii_test.go:
package main
import (
"testing"
"unicode"
)
func isASCIIRange(s string) bool {
for _, c := range s {
if c > unicode.MaxASCII {
return false
}
}
return true
}
func BenchmarkRange(b *testing.B) {
str := ascii()
b.ResetTimer()
for N := 0; N < b.N; N++ {
is := isASCIIRange(str)
if !is {
b.Fatal("notASCII")
}
}
}
func isASCIIIndex(s string) bool {
for i := 0; i < len(s); i++ {
if s[i] > unicode.MaxASCII {
return false
}
}
return true
}
func BenchmarkIndex(b *testing.B) {
str := ascii()
b.ResetTimer()
for N := 0; N < b.N; N++ {
is := isASCIIIndex(str)
if !is {
b.Log("notASCII")
}
}
}
func ascii() string {
byt := make([]byte, unicode.MaxASCII+1)
for i := range byt {
byt[i] = byte(i)
}
return string(byt)
}
Output:
$ go test ascii_test.go -bench=.
BenchmarkRange-4 20000000 82.0 ns/op
BenchmarkIndex-4 30000000 55.4 ns/op
$

Answer 2

It looks like your way is best.
ASCII is simply defined as:
ASCII encodes 128 specified characters into seven-bit integers
As such, characters have values 0-27 (or 0-127, 0x0-0x7F).
Go provides no way to check that every rune in a string (or byte in a slice) has numerical values in a specific range, so your code seems to be the best way to do it.

Answer 3

Another option:
package main
import "golang.org/x/exp/utf8string"
func main() {
{
b := utf8string.NewString("south north").IsASCII()
println(b) // true
}
{
b := utf8string.NewString("🧡💛💚💙💜").IsASCII()
println(b) // false
}
}
https://pkg.go.dev/golang.org/x/exp/utf8string#String.IsASCII