How to check if a string only contains alphabetic characters in Go?

I am trying to check the username whether is only containing alphabetic characters. What is the idiomatic way to check it in Go?

you may use unicode.IsLetter like this working sample code:

package main

import "fmt"
import "unicode"

func IsLetter(s string) bool {
    for _, r := range s {
        if !unicode.IsLetter(r) {
            return false
        }
    }
    return true
}

func main() {
    fmt.Println(IsLetter("Alex")) // true
    fmt.Println(IsLetter("123"))  // false
}

or since go1.21:

package main

import (
    "fmt"
    "strings"
    "unicode"
)

func IsLetter(s string) bool {
    return !strings.ContainsFunc(s, func(r rune) bool {
        return !unicode.IsLetter(r)
    })
}

func main() {
    fmt.Println(IsLetter("Alex"))  // true
    fmt.Println(IsLetter("123 a")) // false

}

or if you have limited range e.g. 'a'..'z' and 'A'..'Z', you may use this working sample code:

package main

import "fmt"

func IsLetter(s string) bool {
    for _, r := range s {
        if (r < 'a' || r > 'z') && (r < 'A' || r > 'Z') {
            return false
        }
    }
    return true
}
func main() {
    fmt.Println(IsLetter("Alex"))  // true
    fmt.Println(IsLetter("123 a")) // false

}

or since go1.21:

package main

import (
    "fmt"
    "strings"
    "unicode"
)

func IsLetter(s string) bool {
    return !strings.ContainsFunc(s, func(r rune) bool {
        return (r < 'a' || r > 'z') && (r < 'A' || r > 'Z')
    })
}

func main() {
    fmt.Println(IsLetter("Alex"))  // true
    fmt.Println(IsLetter("123 a")) // false

}

or if you have limited range e.g. 'a'..'z' and 'A'..'Z', you may use this working sample code:

package main

import "fmt"
import "regexp"

var IsLetter = regexp.MustCompile(`^[a-zA-Z]+$`).MatchString

func main() {
    fmt.Println(IsLetter("Alex")) // true
    fmt.Println(IsLetter("u123")) // false
}