Class Modifiers in Dart 3 | Base, Abstract, Final, Sealed, Mixin

Summary

In this video, we explore Dart 3 class modifiers that control how classes and mixins behave in relation to their libraries. Key modifiers include `abstract`, `base`, `final`, `sealed`, `interface`, and `mixin`. These modifiers impact whether a class can be instantiated, extended, or implemented, allowing developers to structure their code with precise control over inheritance and interface implementation. We also cover practical examples of each modifier, demonstrating how they influence code behavior and structure. This tutorial is essential for mastering Dart's class system and improving code maintainability.

Takeaways

• 😀 Class modifiers in Dart 3 control how a class or mixin can be used, either within its own library or from external libraries.
• 😀 Dart 3 class modifiers include abstract, base, final, interface, sealed, and mixin, each serving distinct purposes for code structuring and access control.
• 😀 A normal class in Dart can be instantiated, extended, or implemented, allowing full flexibility for interaction with other code.
• 😀 Abstract classes cannot be instantiated directly and are meant to be extended or implemented by other classes to define common behavior.
• 😀 Base classes enforce inheritance but disallow implementation from outside their own library, helping control subclass behavior.
• 😀 Interface classes allow implementation but disallow inheritance. They are defined as abstract classes and provide a contract for classes to follow.
• 😀 Final classes can be instantiated but cannot be extended or implemented outside their library, ensuring no further modification or inheritance.
• 😀 Sealed classes restrict the creation of new subtypes outside the class's library but allow subclassing within the library, useful for exhaustiveness checking.
• 😀 Mixins enable code reuse across classes without the limitations of traditional inheritance, allowing the addition of behavior to classes with the `with` keyword.
• 😀 The combination of abstract and interface modifiers can create a pure interface that allows implementation but not inheritance, providing a clear separation of concerns.

Q & A

What are Dart 3 class modifiers used for?

Dart 3 class modifiers control how a class or mixin can be used, either from within its own library or from outside of it. They define the visibility and usage rules of a class or mixin across different libraries.

Can you instantiate a class without any modifier?

Yes, a class without any modifier can be instantiated, extended, or implemented. It is the default behavior for classes in Dart.

What is the difference between `extend` and `implement` in Dart?

`extend` is used for inheritance, where a subclass inherits properties and methods from a superclass, and can override them. `implement` is used to adopt an interface, where a class agrees to implement specific methods defined by the interface.

What is the purpose of an abstract class in Dart?

An abstract class is used to define a behavior that other classes can inherit. It may contain abstract methods (methods without implementation) and cannot be instantiated directly.

Can a base class be instantiated in Dart?

No, a base class cannot be instantiated directly. However, it can be extended to create subclasses, and its methods can be used.

What is the role of the `final` modifier in Dart classes?

A class marked as `final` cannot be extended or implemented outside its own library, but it can still be instantiated. It ensures that no further subclassing occurs.

What is a sealed class, and when would you use it in Dart?

A sealed class is used for exhaustiveness checking, meaning it allows a set of subtypes but restricts inheritance from outside the class. It is useful when you want to ensure all subtypes are covered in a switch statement.

How does a mixin differ from traditional inheritance in Dart?

A mixin allows code reuse across multiple class hierarchies without using traditional inheritance. It enables a class to inherit methods from multiple sources, unlike traditional inheritance, which supports only single class inheritance.

Can a mixin class be extended or have `with` clauses in Dart?

No, a mixin class cannot be extended or have `with` clauses inside it. It is designed solely for reuse in other classes using the `with` keyword.

What is the key difference between `base` and `sealed` classes in Dart?

A `base` class allows inheritance but disallows implementation outside its library, while a `sealed` class restricts both inheritance and instantiation outside its library, ensuring exhaustiveness in pattern matching.