In Dart, runes are a way to represent Unicode code points in a string. They allow you to work with individual Unicode characters, including those that may be represented by more than one UTF-16 code unit. This is particularly useful for handling characters from various languages and symbols that are outside the basic ASCII range.

Understanding Runes

Dart strings are sequences of UTF-16 code units. However, some Unicode characters, especially emoji and certain symbols, require more than one code unit to be represented. Runes provide a means to access these characters as a single unit, using their Unicode code point values.

Creating Runes

You can create a Runes object by using the runes property of a string. The runes property returns an iterable of the Unicode code points represented in that string.

Example:

void main() {
  String str = 'Dart 🦄';
  
  // Accessing runes
  Runes runes = str.runes;
  
  print(runes); // Output: (68, 97, 114, 116, 32, 129412)
}

In this example, the string "Dart 🦄" includes the character "🦄" (unicorn), which is represented by the code point 129412.

Accessing Runes

You can iterate over the runes in a string to access each character by its Unicode code point. Here’s how you can do that:

void main() {
  String str = 'Dart 🦄';

  // Iterating over runes
  for (var rune in str.runes) {
    print(String.fromCharCode(rune)); // Convert each code point back to a string
  }
}

Output:

D
a
r
t
 
🦄

Using Runes in Strings

You can also create a string from a list of runes using the String.fromCharCodes constructor.

Example:

void main() {
  // Creating a string from runes
  List<int> runesList = [68, 97, 114, 116, 32, 129412];
  
  String str = String.fromCharCodes(runesList);
  
  print(str); // Output: Dart 🦄
}

Common Use Cases for Runes

1. Handling Special Characters: When working with strings that include special characters or emoji, using runes ensures you correctly handle all characters regardless of their byte representation.

2. Text Processing: When performing text processing tasks, such as counting characters or searching for specific symbols, accessing runes allows for accurate manipulation based on Unicode characters rather than UTF-16 code units.

3. Internationalization: Runes enable developers to create applications that support multiple languages and scripts, allowing for proper handling of characters from different languages.

Conclusion

Runes in Dart provide a powerful and flexible way to work with Unicode characters in strings. By using runes, you can access, manipulate, and create strings with a diverse range of characters, ensuring your applications can effectively handle internationalization and special character representations. Understanding how to use runes will enhance your ability to work with text in Dart, making your applications more robust and user-friendly.