Bug Report

🔎 Search Terms

A 'this' type is available only in a non-static member of a class or interface.

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about this types. I believe this is a bug (oversight) and not a suggestion because it does already work for what look like very analogous situations.

⏯ Playground Link

Playground link with relevant code

💻 Code

class Foo {
    // Error: A 'this' type is available only in a non-static member of a class or interface.
    badObjWithThisArg(obj: { foo: this }) {}
    badObjWithThisCallback(obj: { foo: (t: this) => this }) {}
    badObjWithThisOutput(): { foo: this } { return { foo: this }; }

    // All fine
    okThisArg(t: this) { }
    okThisCallback(cb: (t: this) => this) {}
    okArrayWithThisArg(a: this[]) { }
    okArrayWithThisCallback(a: ((t: this) => this)[]) { }
    okArrayWithThisOutput(): this[] { return [this]; }
    okIndirectObjWithThisArg(obj: Bar<this>) {}
    okIndirectObjWithThisCallback(obj: Bar<(t: this) => this>) { }
    okIndirectObjWithThisOutput(): Bar<this> { return { foo: this };}
}

interface Bar<T> { 
    foo: T;
}

🙁 Actual behavior

Using { foo: this } as an argument or an output is an error, even in cases where this and other derivatives of this are allowed.

🙂 Expected behavior

Inline object types containing this should be allowed:

1. Exactly the same type is totally legal as long as it is expressed indirectly through a generic interface instead of inline. There is no actual type difference whatsoever between these situations, as far as I understand.
2. Other analogous derivatives such as arrays or functions of this are allowed in the same places.