How to iterate over a String, char by char, in Dart?

Question

I don't see Dart strings treated as lists of characters. I assume I have to use for loops, which would be lame.

Answer 1

An alternative implementation (working with characters outside the basic multilingual plane):

"A string".runes.forEach((int rune) {
  var character=new String.fromCharCode(rune);
  print(character);
});

Answer 2

You could also use the split method to generate a List of characters.

input.split('').forEach((ch) => print(ch));

Answer 3

Unfortunately strings are currently not iterable so you would have to use a for loop like this

for(int i=0; i<s.length; i++) {
  var char = s[i];
}

Note that Dart does not have a character class so string[index] will return another string.

Answer 4

With Flutter Characters Class

import 'package:flutter/material.dart';
var characters = aString.characters;

Answer 5

Extension to properly iterate a String:

extension on String {

  /// To iterate a [String]: `"Hello".iterable()`
  Iterable<String> iterable() sync* {
    for (var i = 0; i < length; i++) {
      yield this[i];
    }}}

Use it like this:

expect("Hello".iterable(), ["H", "e", "l", "l", "o"]);

---

However, if you add the Characters package:

import "package:characters/characters.dart"; 

Then you can have an extension to properly iterate a String using both simple characters or Unicode graphemes:

extension on String {

  /// To iterate a [String]: `"Hello".iterable()`
  /// This will use simple characters. If you want to use Unicode Grapheme
  /// from the [Characters] library, passa [chars] true.
  Iterable<String> iterable({bool unicode = false}) sync* {
    if (unicode) {
      var iterator = Characters(this).iterator;
      while (iterator.moveNext()) {
        yield iterator.current;
      }
    } else
      for (var i = 0; i < length; i++) {
        yield this[i];
      }
  }
}

To prove it works:

  test('String.iterable()', () {
    expect("Hello".iterable(), ["H", "e", "l", "l", "o"]);
    expect("Hello".iterable(unicode: true), ["H", "e", "l", "l", "o"]);

    expect("".iterable().length, 2);
    expect("".iterable().map((s) => s.codeUnitAt(0)), [55357, 56842]);

    expect("".iterable(unicode: true).length, 1);
    expect("".iterable(unicode: true), [""]);
  });

Answer 6

extension on String {
  //toArray1 method
  List toArray1() {
    List items = [];
    for (var i = 0; i < this.length; i++) {
      items.add(this[i]);
    }
    return items;
  }

  //toArray2 method
  List toArray2() {
    List items = [];
    this.split("").forEach((item) => items.add(item));
    return items;
  }
}

main(List<String> args) {
  var str = "hello world hello world hello world hello world hello world";
  final stopwatch1 = Stopwatch()..start();
  print(str.toArray1());
  print('str.toArray1() executed in ${stopwatch1.elapsed}');

  final stopwatch2 = Stopwatch()..start();
  print(str.toArray2());
  print('str.toArray2() executed in ${stopwatch2.elapsed}');


}

The above is the example of using for loop and foreach but the result i tested, foreach is working way faster than for loop. Sorry if i was wrong, but it was my tests.

Answer 7

This also can be the solution : use it if you find it easy

String text = "findlastcharacter";
var array = text.split('');
array.forEach((element) { 
 print(element); // iterating char by char 
});
String lastchar = array[array.length - 1];
print('last char is = $lastchar'); // last char is = r

Thanks

Answer 8

import 'package:characters/characters.dart';  
      
String myString = "Hi";
for (var char in myString.characters) {
   print(char);
}
H
i

One thing to be aware of if you are starting with Characters is that they will be converted to String.

Characters myCharacters = "Hi.characters".characters;      
for (var char in myCharacters) {
        assert(char is String);
        print(char);
}
H
i