Create instances from static method of generic class

Question

I want to have base model:

export class BaseModel<T> {
   public static create(obj:any):T {
      let instance = _.assignIn(new T(), obj);
      return instance;   
   }
}

and then, specific model:

export class MyModel: BaseModel<MyModel> {
   public prop1:string;
}

then, I want to create models in the following way:

let myModel = MyModel.create(...);

But, I can't force it work and get error:

'T' only refers to a type, but is being used as a value here.

The solution is the same - add another parameter to create. Define it like create(cls: {new(): T}, obj: any) { ... assignIn(new cls(), obj); ...}, use it like MyModel.create(MyModel, ...). — artem
– artem, Commented May 10, 2017 at 21:38

Nitzan Tomer · Accepted Answer · 2017-05-10 22:14:03Z

4

You cannot use the generic constraint as a value, it does not exist in runtime, so this:

new T()

Makes no sense.

You can do this:

class BaseModel {
    public static create<T extends BaseModel>(obj: any): T {
        let instance = Object.assign(new this(), obj);
        return instance;
    }
}

(code in playground)

Then

let myModel = MyModel.create<MyModel>(...);

Will work properly.

edited May 10, 2017 at 22:14

answered May 10, 2017 at 21:51

Nitzan Tomer

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1 Comment

user348173 Over a year ago

Thanks for the answer,

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