Скачать или смотреть How to Create a New Instance of a Class in an Abstract Class Constructor in TypeScript

Explore how to create new instances of classes within abstract class constructors in TypeScript, along with an example solution.
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This video is based on the question https://stackoverflow.com/q/69228262/ asked by the user 'Madriesen' ( https://stackoverflow.com/u/11598824/ ) and on the answer https://stackoverflow.com/a/69229015/ provided by the user 'vitoke' ( https://stackoverflow.com/u/11915236/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Class Instantiation in Abstract Classes in TypeScript

In TypeScript, abstract classes play a crucial role in laying down a blueprint for other classes. However, a common question arises: Can you create a new instance of a class in the constructor of an abstract class? Let's tackle this question and provide a clear solution for handling generics in abstract classes.

The Problem

Creating instances in abstract classes can be a bit tricky. The fundamental issue lies in the fact that at runtime, TypeScript lacks the type information necessary to instantiate a specific class type. For instance, consider this code:

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This won't work, as the new T() expression does not have enough information about what T actually is. So, is there a way to effectively create instances in an abstract class constructor? The answer is nuanced but rests on proper construction patterns in TypeScript.

The Solution: Passing the Class Constructor

1. Understanding the Constructor Parameter

Instead of directly referencing the generic type in the constructor, we can pass the class constructor as an argument. This method provides the needed information to create an instance of the specified class. Here's how to revise the abstract class:

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In this code:

cls is a parameter that takes a class constructor.

new cls() allows TypeScript to create a new instance of the class provided.

2. Extending the Abstract Class

Now that we have our abstract class set up, we can create a class that extends it. Let’s take a look at an example:

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Here’s a breakdown of what happens in ExtendBaseClass:

When ExtendBaseClass is instantiated, it calls super(MyClass), which allows BaseClass to create an instance of MyClass.

The accessGenericClass function can then easily access the properties of MyClass through this.genericClass.

3. Summary of Steps

To summarize:

Abstract classes provide a structure but cannot instantiate classes directly in their constructors due to the lack of runtime type information.

Constructor Parameters: Always pass the specific class constructor to enable instance creation.

Extending: Use the base class in derived classes to create specific instances as needed.

Conclusion

Creating instances in an abstract class constructor is not as straightforward as it may seem, but with the right approach, it can be effectively managed. By passing the class constructor, you can utilize TypeScript's generics while maintaining the structure that abstract classes provide. Now you have a powerful tool in your TypeScript toolkit for building flexible and reusable class structures.

This solution is far from “stupid”; it demonstrates how to approach challenges in TypeScript, ultimately enhancing your coding skills!