Weird behavior of string methods in dart

Question

I am trying to check for the index of a character "-" in a string variable. Despite the fact that the variable contains "-", dart indexof and lastIndexof are returning -1. I also checked with "contain" method it is equally returning that string does not contain "-" despite the fact it does. Here is the code:

     String s = "Oh yes, the past can hurt. But the way I see it, you can either run from it or learn from it. – The Lion King";
         int x = s.indexOf('-');
        print(x);
         if(s.contains("-")){
          // print("vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv............");
           print("Yipee string contains -");
         }else{
           print("string does not contain -");
              // the following is the output:
             //string does not contain -
         }
     
         if(x == -1){
         print(x);
         // It prints out -1 
        }else{
           
          print(x);
           return s.substring(0,x);
         }

Please for the love of God, what am i doing wrong?

Answer 1

'–' and '-' are two different characters. See how the first one is slightly longer.

void main() {
  final str = '–-';
  print(str.codeUnitAt(0)); // 8211 (En Dash)
  print(str.codeUnitAt(1)); // 45 (Hyphen)
}

If you want to find either one or the other, you can also use Regular Expressions :

In the following code sample, str1 and str2 are almost the same. I just inverted the position of '–' and '-' .

void main() {
  final str1 = '123456–78-90';
  final str2 = '123456-78–90';
  final regExp = RegExp(r'[–-]');
  print(regExp.firstMatch(str1)?.start); // 6
  print(regExp.firstMatch(str2)?.start); // 6
}

Answer 2

The character - you are searching for is different than the character – in the text. Notice the length difference between the two.

Answer 3

The character present in the string is an en dash and is slightly wider than the hyphen (-) but narrower than the em dash (—). Due to this the contains function is not able to detect hyphen as en dash is present.