With Polymorphic this in TypeScript 1.7, as I discovered here, we can define a method in a class with a return type of this
, and automatically, any classes that extend that class and inherit the methods, will have their return types set to their respective this
type. Like so:
class Model {
save():this { // return type: Model
// save the current instance and return it
}
}
class SomeModel extends Model {
// inherits the save() method - return type: SomeModel
}
However, what I'm after is to have an inherited static
method with a return type referencing the class itself. It's best described in code:
class Model {
static getAll():Model[] {
// return all recorded instances of Model as an array
}
save():this {
// save the current instance and return it
}
}
class SomeModel extends Model {
// inherits the save() method - return type: SomeModel
// also inherits getAll() - return type: Model (how can we make that SomeModel?)
}
Perhaps I'll have to think of a different way to implement this, since Polymorphic this
in TypeScript 1.7 does not support static
methods by design.
EDIT: I guess we'll see how this Github issue wraps up: https://github.com/Microsoft/TypeScript/issues/5863
This is doable in TypeScript 2.0+. By using an inline { new(): T }
type to capture this
, you'll get what you wanted:
type Constructor<T> = { new (): T }
class BaseModel {
static getAll<T>(this: Constructor<T>): T[] {
return [] // dummy impl
}
/**
* Example of static method with an argument:
*/
static getById<T>(this: Constructor<T>, id: number): T | undefined {
return // dummy impl
}
save(): this {
return this // dummy impl
}
}
class SubModel extends BaseModel {}
const sub = new SubModel()
const savedSub: SubModel = sub.save()
// Behold: SubModel.getAll() returns SubModels, not BaseModel
const savedSubs: SubModel[] = SubModel.getAll()
Note that getAll
still expects no arguments with this typing.
For more information, see https://www.typescriptlang.org/docs/handbook/2/generics.html#using-class-types-in-generics and https://stackoverflow.com/a/45262288/1268016