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.

Solution 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);
});

Solution 2

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

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

Solution 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.

Solution 4

With Flutter Characters Class

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

Solution 5

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.

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Comments

[CedX]

Warning: with some rare foreign languages, the loop does not work as expected. length property and [] operator refers to UTF-16 code units, not characters. Some characters can use 2 UTF-16 code units.

[CedX]

Starting with Dart 2.7.0, you can use the package characters: pub.dev/packages/characters.

[lordvidex]

BonusPoint:: getter codeUnits can also be used in place of runes as in:"A string".codeUnits.forEach((int c) { var character=new String.fromCharCode(c); print(character); });

[CedX]

String.codeUnits only deals with UTF-16 code points, whereas String.runes deals with Unicode code points (UTF-8, UTF-16, UTF-32). A character can be represented by 2 UTF-16 code points (i.e. a surrogate pair), but will be represented by only 1 rune.

[lrn]

The Flutter link is a re-export of package:characters/characters.dart which can be used without Flutter too. It is the recommended way to iterate general Unicode text.