104 lines
2.0 KiB
Markdown
104 lines
2.0 KiB
Markdown
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# Generics in Dart: A Comprehensive Guide
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Generics allow you to write flexible, reusable code that can work with different types while maintaining type safety.
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## 1. Generic Classes
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You can create classes that work with different types by using type parameters.
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### Example:
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```dart
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class Box<T> {
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T contents;
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Box(this.contents);
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T getContents() {
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return contents;
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}
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}
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void main() {
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var intBox = Box<int>(42);
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var stringBox = Box<String>("Hello");
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print(intBox.getContents()); // Prints 42
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print(stringBox.getContents()); // Prints Hello
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}
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```
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## 2. Generic Methods
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Methods can also use generics to work with different types.
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### Example:
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```dart
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T first<T>(List<T> list) {
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if (list.isEmpty) {
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throw StateError("List is empty");
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}
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return list[0];
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}
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void main() {
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var numbers = [1, 2, 3];
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var strings = ["a", "b", "c"];
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print(first(numbers)); // Prints 1
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print(first(strings)); // Prints a
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}
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```
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## 3. Type Bounds
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You can restrict the types that can be used with a generic by using type bounds.
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### Example:
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```dart
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class NumberBox<T extends num> {
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T value;
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NumberBox(this.value);
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void square() {
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print(value * value);
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}
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}
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void main() {
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var intBox = NumberBox<int>(5);
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var doubleBox = NumberBox<double>(2.5);
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intBox.square(); // Prints 25
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doubleBox.square(); // Prints 6.25
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// var stringBox = NumberBox<String>("Hello"); // Compile-time error
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}
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```
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## 4. Generic Collections
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Dart's collection types are all generic.
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### Example:
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```dart
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void main() {
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List<int> numbers = [1, 2, 3];
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Map<String, int> ages = {"Alice": 30, "Bob": 25};
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Set<double> scores = {9.5, 8.7, 9.2};
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numbers.add(4); // OK
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// numbers.add("5"); // Compile-time error
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print(ages["Alice"]); // Prints 30
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print(scores.contains(9.2)); // Prints true
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}
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```
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## Conclusion
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Generics in Dart provide a powerful way to write reusable, type-safe code. They are extensively used in Dart's core libraries and are a fundamental concept for writing efficient and flexible Dart and Flutter applications.
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