package validate import ( "errors" "strings" ) // Validation error. var ( ErrDisallowedChars = errors.New("contains disallowed characters") ) // Chars validates whether a string contains only allowed characters. func Chars(allow string) func(string) error { return func(value string) error { rs := []rune(value) for _, r := range rs { if !strings.ContainsRune(allow, r) { return ErrDisallowedChars } } return nil } }