How to check if a string is all upper or lower case in Go? - string

Question

What is an easy way in Golang to check if all characters in a string are upper case or lower case?
Also, how to handle a case where the string has punctuation?
See these examples:
package main
import (
"fmt"
"unicode"
)
func main() {
s := "UPPERCASE"
fmt.Println(s.IsUpper()) // Should print true
s = "lowercase"
fmt.Println(s.IsUpper()) // Should print false
s = "lowercase"
fmt.Println(s.IsLower()) // Should print true
s = "I'M YELLING AT YOU!"
fmt.Println(s.IsUpper()) // Should print true
}
Note: s.IsUpper() and s.IsLower() doesn't really exist, but would be nice to find an equivalent.

Answer 1

You can of course compare the upper and lower cased strings in their entirety, or you can short-circuit the comparisons on the first failure, which would be more efficient when comparing long strings.
func IsUpper(s string) bool {
for _, r := range s {
if !unicode.IsUpper(r) && unicode.IsLetter(r) {
return false
}
}
return true
}
func IsLower(s string) bool {
for _, r := range s {
if !unicode.IsLower(r) && unicode.IsLetter(r) {
return false
}
}
return true
}

Answer 2

One solution is to use strings.ToUpper()/ToLower() and compare with the original string. This works for the punctuation case as well.
Here's the solution:
package main
import (
"fmt"
"strings"
)
func main() {
s := "UPPERCASE"
fmt.Println(strings.ToUpper(s) == s)
s = "lowercase"
fmt.Println(strings.ToUpper(s) == s)
s = "lowercase"
fmt.Println(strings.ToLower(s) == s)
s = "I'M YELLING AT YOU!"
fmt.Println(strings.ToUpper(s) == s)
}

Answer 3

A unicode.{IsUpper, Lower} and B strings.{ToUpper, Lower} both good
For the data composed of single bytes, A will be better than B
If the data byte is unsure then B is better than A: for example 中文a1
package main
import (
"strings"
"testing"
"unicode"
)
func IsUpperU(s string) bool {
for _, r := range s {
if !unicode.IsUpper(r) && unicode.IsLetter(r) {
return false
}
}
return true
}
func IsUpper(s string) bool {
return strings.ToUpper(s) == s
}
func IsLowerU(s string) bool {
for _, r := range s {
if !unicode.IsLower(r) && unicode.IsLetter(r) {
return false
}
}
return true
}
func IsLower(s string) bool {
return strings.ToLower(s) == s
}
func TestIsUpper(t *testing.T) {
for _, d := range []struct {
actual bool
expected bool
}{
{IsUpperU("中文A1"), false}, // be careful!
{IsUpper("中文A1"), true},
{IsUpper("中文a1"), false},
{IsUpperU("中文a1"), false},
} {
if d.actual != d.expected {
t.Fatal()
}
}
}
func TestIsLower(t *testing.T) {
for idx, d := range []struct {
actual bool
expected bool
}{
{IsLowerU("中文a1"), false}, // be careful!
{IsLower("中文a1"), true},
{IsLower("中文A1"), false},
{IsLowerU("中文A1"), false},
} {
if d.actual != d.expected {
t.Fatal(idx)
}
}
}
go playground

Answer 4

No need for unicode (For English letters only):
func IsUpper(s string) bool {
for _, charNumber := range s {
if charNumber > 90 || charNumber < 65 {
return false
}
}
return true
}
func IsLower(s string) bool {
for _, charNumber := range s {
if charNumber > 122 || charNumber < 97 {
return false
}
}
return true
}