Instance of array property in generic class?

Question

I have a generic class of typescript with 2 properties as -

export class WrapperModel<T>{
    constructor(private testType: new () => T) {
        this.getNew();
    }

    getNew(): T {
        return new this.testType();
    }
    public Entity: T;
    public ShowLoading: boolean;
}

Then using it as follows -

this.userModel = new WrapperModel<UserProfileModel>(UserProfileModel);

I am assuming it is creating an instance of type UserProfileModel in its constructor.

But when I try with Array type property then it fails. Like when I do -

this.userModel = new WrapperModel<Array<UserProfileModel>>(Array<UserProfileModel>);

The error which I get in above case -

Is it I cannot create an instance of Array property in generics or something else. My need is simple; I want to create instance of Array properties in Generic class.

Titian Cernicova-Dragomir · Accepted Answer · 2017-12-12 12:55:56Z

1

The problem is that that at runtime generics are erased, so Array<UserProfileModel> is not really a constructor function, Array is the constructor function so you can write:

var userModel = new WrapperModel<Array<UserProfileModel>>(Array);

This applies for any generic type, not just array:

class Generic<T> {  }
var other = new WrapperModel<Generic<UserProfileModel>>(Generic);

Generally for a generic class there does not appear to be a way to get a constructor for specific type instantiation, only the generic constructor:

// Valid, new get a generic constrcutor
var genericCtor: new <T>() => Generic<T> = Generic;

// Not valid,  Generic<UserProfileModel> is not callable
var genericCtor: new () => Generic<UserProfileModel> = Generic<UserProfileModel>;

edited Dec 12, 2017 at 12:55

answered Dec 12, 2017 at 12:42

Titian Cernicova-Dragomir

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4 Comments

Manoz Over a year ago

It worked thanks. Is it only pass typeof argument for all generic types?

Titian Cernicova-Dragomir Over a year ago

Sorry not sure I understand the question

Manoz Over a year ago

I meant to say what if I pass only type of argument as - this.userModel = new WrapperModel<UserProfileModel>(object) <-- object is passed since the type argument is removed right?

Titian Cernicova-Dragomir Over a year ago

You have to pass the class without generic arguments, that does not mean any generic class would too, typescript still checks compatibility, so this will give an error:

class Generic<T> { public foo: number } class Generic2<T> { public foo2: number } var other = new WrapperModel<Generic<UserProfileModel>>(Generic2);

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