100 lines
2.2 KiB
Markdown
100 lines
2.2 KiB
Markdown
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# Extension Methods in Dart: A Comprehensive Guide
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Extension methods allow you to add new functionality to existing libraries or classes without modifying their source code.
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## 1. Creating an Extension
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To create an extension, use the `extension` keyword followed by the extension name and the type you're extending.
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### Example:
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```dart
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extension StringExtension on String {
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String capitalize() {
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return '${this[0].toUpperCase()}${this.substring(1)}';
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}
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}
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```
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## 2. Using an Extension
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Once defined, you can use the extension method as if it were a part of the original class.
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### Example:
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```dart
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void main() {
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String name = 'john';
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print(name.capitalize()); // Prints: John
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}
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```
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## 3. Extension on Built-in Types
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You can add extensions to any type, including built-in types like `int` or `List`.
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### Example:
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```dart
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extension IntExtension on int {
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bool isEven() => this % 2 == 0;
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}
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extension ListExtension<T> on List<T> {
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T getRandomElement() => this[DateTime.now().microsecond % length];
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}
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void main() {
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print(42.isEven()); // Prints: true
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var fruits = ['apple', 'banana', 'orange'];
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print(fruits.getRandomElement()); // Prints a random fruit
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}
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```
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## 4. Naming Conflicts
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If there's a naming conflict, you can use the `hide` keyword to resolve it.
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### Example:
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```dart
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extension MyStringExtension on String {
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bool isLong() => length > 10;
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}
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extension AnotherStringExtension on String {
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bool isLong() => length > 20;
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}
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void main() {
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String text = 'Hello, World!';
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// Use specific extension
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print(MyStringExtension(text).isLong()); // Prints: true
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print(AnotherStringExtension(text).isLong()); // Prints: false
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// Or hide one extension
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import 'my_extensions.dart' hide MyStringExtension;
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}
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```
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## 5. Static Extension Methods
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You can also define static extension methods.
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### Example:
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```dart
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extension NumberParsing on String {
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static int parseInt(String input) => int.parse(input);
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}
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void main() {
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print(NumberParsing.parseInt('42')); // Prints: 42
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}
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```
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## Conclusion
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Extension methods provide a clean way to add functionality to existing types without modifying their source code. They are particularly useful when working with types from external libraries or core Dart types that you can't modify directly.
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