Preventing me from instantiating objects

Question

Preventing me from instantiating objects

I've been struggling with an issue for a while now

consider the following:

export abstract class abstractClass {
    abstract thing(): string
}

export class c1 extends abstractClass {
    thing(): string {
        return "hello"
    }
}

export class c2 extends abstractClass {
    thing(): string {
        return "world"
    }
}

export interface simpleInter {
    el: typeof abstractClass
}

const cls: simpleInter[] = [];
cls.push({
    el: c1
},{
    el: c2
})

for (const classObj of cls) {
    const c = new (classObj.el)() // error: Cannot create an instance of an abstract class. ts(2511)
    console.log(c.thing())
}

What baffles me is how can I instruct the compiler to recognize that I want classes which extend my abstractClass as the type.

typescript class interface abstract typeof

Answer 1

Answer №1

To ensure proper implementation of your concrete classes, define a constructor function interface called CConstructor and use it as the base type instead of typeof abstractClass. By following this approach, you will be on the right track.

export interface CConstructor {
    new(): abstractClass
}

export abstract class abstractClass {
    abstract thing(): string
}

export class c1 extends abstractClass {
    thing(): string {
        return "greetings"
    }
}

export class c2 extends abstractClass {
    thing(): string {
        return "universe"
    }
}

const cls: CConstructor[] = [c1, c2];

for (const classObj of cls) {
    const c = new (classObj)()
    console.log(c.thing())
}

Update:

The presence of new(): abstractClass within CConstructor denotes a "Construct Signature," which can be created by prefixing a call signature with the keyword new. For further details, refer to the new TS handbook page.

Answer 2

To ensure proper implementation of your concrete classes, define a constructor function interface called CConstructor and use it as the base type instead of typeof abstractClass. By following this approach, you will be on the right track.

export interface CConstructor {
    new(): abstractClass
}

export abstract class abstractClass {
    abstract thing(): string
}

export class c1 extends abstractClass {
    thing(): string {
        return "greetings"
    }
}

export class c2 extends abstractClass {
    thing(): string {
        return "universe"
    }
}

const cls: CConstructor[] = [c1, c2];

for (const classObj of cls) {
    const c = new (classObj)()
    console.log(c.thing())
}

Update:

The presence of new(): abstractClass within CConstructor denotes a "Construct Signature," which can be created by prefixing a call signature with the keyword new. For further details, refer to the new TS handbook page.

Answer 3

Answer №2

It seems like you are looking to dynamically instantiate your classes. If you need more information on this topic, you can refer to: Dynamic instantiation in JavaScript

For autocompletion, you can cast later to the desired object.

I'm not entirely sure if this will solve your problem, but it might bring you closer to a solution:

interface simpleInter {
  el: string;
}

const cls: simpleInter[] = [];
cls.push({
  el: 'c1'
},{
  el: 'c2'
});

function instantiate(className: string, args: any) {
  var o, f, c;
  c = window[className]; // get reference to class constructor function
  f = function(){}; // dummy function
  f.prototype = c.prototype; // reference same prototype
  o = new f(); // instantiate dummy function to copy prototype properties
  c.apply(o, args); // call class constructor, supplying new object as context
  o.constructor = c; // assign correct constructor (not f)
  return o;
}

for (const classObj of cls) {
  const c = instantiate(classObj.el, []); // error: Cannot create an instance of an abstract class. ts(2511)
  console.log(c.thing());
}

Answer 4

It seems like you are looking to dynamically instantiate your classes. If you need more information on this topic, you can refer to: Dynamic instantiation in JavaScript

For autocompletion, you can cast later to the desired object.

I'm not entirely sure if this will solve your problem, but it might bring you closer to a solution:

interface simpleInter {
  el: string;
}

const cls: simpleInter[] = [];
cls.push({
  el: 'c1'
},{
  el: 'c2'
});

function instantiate(className: string, args: any) {
  var o, f, c;
  c = window[className]; // get reference to class constructor function
  f = function(){}; // dummy function
  f.prototype = c.prototype; // reference same prototype
  o = new f(); // instantiate dummy function to copy prototype properties
  c.apply(o, args); // call class constructor, supplying new object as context
  o.constructor = c; // assign correct constructor (not f)
  return o;
}

for (const classObj of cls) {
  const c = instantiate(classObj.el, []); // error: Cannot create an instance of an abstract class. ts(2511)
  console.log(c.thing());
}

Preventing me from instantiating objects

Answer №1

Answer №2

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