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Ildeberto Silva
Ildeberto Silva

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Dart 3.3 news: what are Extension Types?

  • They’re a way to enhance existing types with specialized methods and properties without incurring the memory overhead of typical wrapper classes.
  • Think of them as lightweight “extensions” that add functionality like custom getters, setters, operators, and functions specifically tailored to the underlying type.

Key Advantages:

**Enhanced Performance: **They avoid creating dedicated objects (wrappers) for each instance, making them ideal for performance-sensitive scenarios, especially when dealing with large datasets or frequent data manipulation.

Clearer Abstraction: You can create clean Dart-like APIs to hide the complexities of underlying representation types, promoting better code readability and maintainability.

Simplified Interoperability: They streamline working with native platform types (host platforms). You can interact with them directly, eliminating the need for separate wrappers and reducing potential performance bottlenecks.
syntax and Usage

extension type NumberExtension(int i) {
  // Custom methods and properties specific to integers
  bool isEven() => i % 2 == 0;
  String doubleIt() => 'Double: ${i * 2}';

void main() {
  final number = NumberExtension(13); // Use extension type notation

    print('Double it : ${number.doubleIt()}');
    print('Is Even: ${number.isEven()}');

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Key Points:

  • **They’re zero-cost: **Dart generates code as if you were working with the underlying type directly.
  • They define a new type, distinct from the underlying type, but provide type safety.

  • They can’t change the behavior of the existing type’s properties and methods.


Differences Between Extension Types and Extension Methods:


  • Extension Methods:

Allow adding methods and properties to existing types without creating a new type.
Are lightweight and suitable for adding simple functionalities.
Cannot be used to define a new type with entirely different behavior.
Extension Types:

Allow creating a new type that encapsulates the original type and provides a customized API.
Are more powerful and can be used to add complex functionalities.
Are ideal for interoperability with native platforms and performance optimization.
that is:

  • Extension Methods are ideal for adding simple functionalities to existing types.
  • Extension Types are ideal for creating custom APIs and optimizing performance. example:


Suppose we want to add an isEven() method to check if a number is even.

With Extension Methods:

extension IsEven on int {
  bool isEven() => this % 2 == 0;

void main() {
  final number = 42;
  print(number.isEven()); // true
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With Extension Types:

extension type EvenNumber(int i) {
  bool isEven() => i % 2 == 0;

void main() {
  final number = EvenNumber(42);
  print(number.isEven()); // true
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In this example, both solutions work, but the latter is more robust and flexible. By using an Extension Type, we can create a new type EvenNumber with specific behavior. This can be useful for interoperability with native platforms or for performance optimization.

Other differences:

  • Extension Types can have constructors, while Extension Methods cannot.

In general:

  • Use Extension Methods for simple functionalities.
  • Use Extension Types for complex functionalities, interoperability with native platforms, or performance optimization.
  • In Conclusion:
  • Extension Types are a powerful tool for performance optimization, code clarity, and seamless interoperability in Dart 3.3. They empower you to create highly efficient and well-structured applications, especially when dealing with native code or performance-critical domains

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