Instantiate a child class within an abstract class by utilizing the keyword "this"

Question

Instantiate a child class within an abstract class by utilizing the keyword "this"

Within my code, there is an abstract class that uses new this(). Surprisingly, this action is not creating an instance of the abstract class itself but is generating an instance of the class that inherits from it.

Even though this behavior is acceptable in JavaScript when compiled, TypeScript is not pleased with it.

The error thrown is: "Cannot create an instance of an abstract class."

abstract class Model {
  static find<T extends Model>(someVar) {
    let inst = new this() as T
    // Additional operations applied to the instance
    return inst
  }
}

class A extends Model { }

A.find()

javascript typescript

Answer 1

Answer №1

The primary issue with your current solution is its lack of safety as the T type may not have an empty constructor. Another problem arises when calling the find() method on the A class, as the return type will default to Model if not explicitly set.

To address these issues, it is recommended to pass the type constructor to the find method when specifying the A type. This approach ensures that both problems are resolved effectively.

abstract class Model {
  static find<T extends Model>(ModelClass: new () => T, param: string): T {
    let inst = new ModelClass()
    // Additional operations can be performed on the instance here
    return inst;
  }
}

class A extends Model {}
const a = Model.find(A, "param");

Answer 2

The primary issue with your current solution is its lack of safety as the T type may not have an empty constructor. Another problem arises when calling the find() method on the A class, as the return type will default to Model if not explicitly set.

To address these issues, it is recommended to pass the type constructor to the find method when specifying the A type. This approach ensures that both problems are resolved effectively.

abstract class Model {
  static find<T extends Model>(ModelClass: new () => T, param: string): T {
    let inst = new ModelClass()
    // Additional operations can be performed on the instance here
    return inst;
  }
}

class A extends Model {}
const a = Model.find(A, "param");

Instantiate a child class within an abstract class by utilizing the keyword "this"

Answer №1

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