> ## Documentation Index > Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt > Use this file to discover all available pages before exploring further. # Dart String A Dart `String` is an immutable sequence of UTF-16 code units. It represents text data and provides a robust set of built-in properties and methods for string manipulation, supporting both standard character encoding and complex Unicode scalar values. ## String Literals Dart supports multiple literal formats to accommodate different formatting and escaping requirements. Strings can be defined using single or double quotes. ```dart theme={"dark"} String singleQuote = 'A string literal'; String doubleQuote = "Another string literal"; ``` **Multiline Strings** Triple quotes (either single or double) create multiline strings, preserving whitespace and line breaks exactly as authored in the source code. ```dart theme={"dark"} String multiline = ''' This is a multiline string '''; ``` **Raw Strings** Prefixing a string literal with `r` creates a raw string. Raw strings ignore escape sequences (like `\n` or `\t`), treating them as literal characters. ```dart theme={"dark"} String rawString = r'This will print the \n literally.'; ``` ## String Interpolation Dart evaluates expressions embedded within string literals using the `$` or `${}` syntax. The language implicitly invokes the `toString()` method on the evaluated object. The curly braces can be omitted for simple identifiers. ```dart theme={"dark"} int value = 42; String simple = 'The value is $value'; String expression = 'The hex value is ${value.toRadixString(16)}'; ``` ## Concatenation Strings can be concatenated using the `+` operator. Additionally, Dart supports implicit concatenation of adjacent string literals, which is evaluated at compile time. ```dart theme={"dark"} // Operator concatenation String combined = 'Hello' + ' ' + 'World'; // Adjacent literal concatenation (compile-time) String adjacent = 'Hello' ' ' 'World'; ``` ## Immutability Strings in Dart are strictly immutable. Once a `String` object is created in memory, its state cannot be altered. Any method that performs a transformation (e.g., `substring`, `replaceAll`, `toLowerCase`) allocates and returns a completely new `String` object. ```dart theme={"dark"} String original = 'Dart'; // The following creates a new string; 'original' remains 'Dart' String modified = original.toUpperCase(); ``` ## Internal Representation: Code Units and Runes Because Dart strings are UTF-16, characters within the Basic Multilingual Plane (BMP) are represented by a single 16-bit code unit. However, characters outside the BMP (such as emojis or specific mathematical symbols) require two code units, known as a surrogate pair. To safely iterate over or manipulate complex Unicode characters without splitting surrogate pairs, Dart provides the `runes` property, which exposes an iterable of UTF-32 code points. ```dart theme={"dark"} String emoji = '🚀'; // Length in UTF-16 code units (Returns 2, due to surrogate pair) int unitLength = emoji.length; // UTF-16 code units: [55357, 56960] List codeUnits = emoji.codeUnits; // Length in UTF-32 code points (Returns 1) int runeLength = emoji.runes.length; // UTF-32 code points: (128640) Iterable runes = emoji.runes; ```

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