Type 'this'???

[electricessence]

Is there any magic (without insane generics) to define a type that matches 'this'?

For example...

class A {
  me():A {
     return this;
  }
}

class B extends A {
  otherThing():void{}
  me():B {
    return this;
  }
}

Instead of overriding me() can I define a type without adding another generic declaration that simply solves the type of me()?

[mhegazy]

this?

class A {
  me(): this {
     return this;
  }
}

[electricessence]

So I tried that and it started to unravel when I got into sub classes...
I want 'this' as a type to reflect the current type... Is that what : this is doing?

[mhegazy]

What do you mean by "current type"; and what happened with subclasses when you used this?

[basarat]

I want 'this' as a type to reflect the current type... Is that what : this is doing?

Yes.

class A {
  me():this {
     return this;
  }
}

class B extends A {
  otherThing():void{}
  me():this {
    return this;
  }
}

let a = new A, b= new B();
let foo = a.me(); // foo:A
let bar = b.me(); // bar:B

You can hover over foo / bar in your IDE to see the inferred type 🌹

[basarat]

Also, you don't need to override it i.e. the base case me function is enough 🌹

class A {
  me():this {
     return this;
  }
}

class B extends A {
  otherThing():void{}  
}

let a = new A, b= new B();
let foo = a.me(); // foo:A
let bar = b.me(); // bar:B

[mhegazy]

also, this types are infered automatically for you:

class A {
  me() {
     return this; // infers type this
  }
}

[DanielRosenwasser]

https://www.typescriptlang.org/docs/handbook/advanced-types.html#polymorphic-this-types

[electricessence]

Hey thanks guys! I'm gonna check this out. It may make a huge difference in some of my class structures. I did try and do this out of instinct, but it didn't work right on my first try. I'll get back to you. ;)

[electricessence]

Ok so here's where it get's sticky...

class A<T> {
  me():this {
     return this;
  }
}

class B<T> extends A<T> {
  otherThing():void{}  
}

class C<T> extends B<T> {
  map<TResult>(t:(v:T)=>TResult):this<TResult> {}
}

Anything that will make this work? :/

[basarat]

Minor simplification of your code (that still errors):

class A<T> {
    map<TResult>(mapper: (v: T) => TResult): this<TResult>{

    }
}

However this really is whatever calls the function generics and all, so I don't see a way to declare what you want 🌹

[electricessence]

Yes, you get it.
Ok so it means that I have to override the function.

So lastly is there any consequences to doing something like:

class A<T> {
    clone():this {
       return new A<T>();
    }
}

[basarat]

So lastly is there any consequences to doing something like:

If a child class B fails to override it then the compiler will think new B().clone() to be B but it will really be A 🌹

[electricessence]

Ok so assuming that it the type returned always matches correctly, then ok right?
Because right now, for the above sample I have to force the return like this (to get it to compile):

class A<T> {
    clone():this {
       return <any> new A<T>();  // without <any> it complains.
    }
   me():this {
      return this; // doesn't complain
   }
}

[electricessence]

So I got everything to compile.