Problem with this type

[tao-cumplido]

TypeScript Version: 2.9.2, 3.1.1 (didn't try any other)

Search Terms:
this type
keyof this

Code

interface Foo {
    foo: number;
}

interface Bar {
    bar: number;
}

type FooBar = Partial<Foo & Bar>;
type FooBarMap<T extends FooBar> = { [P in Extract<keyof FooBar, keyof T>]: string };

declare function map<T extends FooBar>(o: T): FooBarMap<T>;

class A implements Foo {
    foo = 1;
    map = map(this);
    constructor() {
        console.log(this.map.foo) // unexpected: Property 'foo' does not exist on type 'FooBarMap<this>'.
        console.log(this.map.bar) // expected: Property 'bar' does not exist on type 'FooBarMap<this>'.
    }
}

class B implements Bar {
    bar = 1;
    map = map(this as B);
    constructor() {
        console.log(this.map.foo); // expected: Property 'foo' does not exist on type 'FooBarMap<B>'.
        console.log(this.map.bar);
    }
}

Expected behavior:
map(this) should be the same as map(this as A) for class A;

Actual behavior:
See code above or Playground.

I suspected the problem might be keyof this vs. keyof A, but I didn't manage to reduce the problem to it so I'm not sure.

Playground Link:
Link

Related Issues:
#24791

[ghost]

I think this is the same problem as #27883. { [P in Extract<keyof FooBar, keyof T>]: string }; should contain at least "foo", but we don't have a way to represent that.

[tao-cumplido]

@andy-ms
I must admit, I don't think I fully grasp the issue you referenced, but I'm not sure they are related.

My problem here is that map(this) infers to map<this>(this) and it behaves differently than map<A>(this), i.e. when I use the explicit forms map<A>(this) or map(this as A) then it works as expected. But from my understanding the type this and the type A should behave the same, at least in the case above, or not?

[typescript-bot]

This issue has been marked as a duplicate and has seen no activity in the last day. It has been closed for automatic house-keeping purposes.