Polymorphic "this" for static members

When trying to implement a fairly basic, but polymorphic, active record style model system we run into issues with the type system not respecting `this` when used in conjunction with a constructor or template/generic. I've posted before about this here, #5493, and #5492 appears to mention this behavior also. And here is an SO post this that I made: http://stackoverflow.com/questions/33443793/create-a-generic-factory-in-typescript-unsolved I have recycled my example from #5493 into this ticket for further discussion. I wanted an open ticket representing the desire for such a thing and for discussion but the other two are closed. Here is an example that outlines a model `Factory` which produces models. If you want to customize the `BaseModel` that comes back from the `Factory` you should be able to override it. However this fails because `this` cannot be used in a static member. ``` typescript // Typically in a library export interface InstanceConstructor<T extends BaseModel> { new(fac: Factory<T>): T; } export class Factory<T extends BaseModel> { constructor(private cls: InstanceConstructor<T>) {} get() { return new this.cls(this); } } export class BaseModel { // NOTE: Does not work.... constructor(private fac: Factory<this>) {} refresh() { // get returns a new instance, but it should be of // type Model, not BaseModel. return this.fac.get(); } } // Application Code export class Model extends BaseModel {

Posted by tlong-dev on Dec 1, 2015, 8:23 PM

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