Dart Programming - Runes

Strings are a sequence of characters. Dart represents strings as a sequence of Unicode UTF-16 code units. Unicode is a format that defines a unique numeric value for each letter, digit, and symbol.

Since a Dart string is a sequence of UTF-16 code units, 32-bit Unicode values within a string are represented using a special syntax. A rune is an integer representing a Unicode code point.

The String class in the dart:core library provides mechanisms to access runes. String code units / runes can be accessed in three ways −

• Using String.codeUnitAt() function
• Using String.codeUnits property
• Using String.runes property

String.codeUnitAt() Function

Code units in a string can be accessed through their indexes. Returns the 16-bit UTF-16 code unit at the given index.

Syntax

String.codeUnitAt(int index);

Example

import 'dart:core'; 
void main(){ 
   f1(); 
} 
f1() { 
   String x = 'Runes'; 
   print(x.codeUnitAt(0)); 
}

It will produce the following output −

82

String.codeUnits Property

This property returns an unmodifiable list of the UTF-16 code units of the specified string.

Syntax

String. codeUnits;

Example

import 'dart:core';  
void main(){ 
   f1(); 
}  
f1() { 
   String x = 'Runes'; 
   print(x.codeUnits); 
} 

It will produce the following output −

[82, 117, 110, 101, 115]

String.runes Property

This property returns an iterable of Unicode code-points of this string.Runes extends iterable.

Syntax

String.runes

Example

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

It will produce the following output −

A 
s 
t 
r 
i 
n 
g

Unicode code points are usually expressed as \uXXXX, where XXXX is a 4-digit hexadecimal value. To specify more or less than 4 hex digits, place the value in curly brackets. One can use the constructor of the Runes class in the dart:core library for the same.

Example

main() { 
   Runes input = new Runes(' \u{1f605} '); 
   print(new String.fromCharCodes(input)); 
}  

It will produce the following output −