Intersection type from Function and object literal type doesn't work

[cshaa]

TypeScript Version: 2.7.2

Search Terms: Function interface, object literal type, intersection, type alias

Code

type MyConstructorType = Function & {prototype: {foo: number}};
let bar = (function () { }) as MyConstructorType;
bar.prototype.foo();

or equivalent:

let bar = (function () { }) as Function & {prototype: {foo: number}};
bar.prototype.foo();

doesn't even depend on the order

let bar = (function () { }) as {prototype: {foo: number}} & Function;
bar.prototype.foo();

Expected behavior:
The function call bar.prototype.foo() should throw a compile time error, as foo is marked as a number.

Actual behavior:
The property bar.prototype is of type any, no matter the intersection type.

Playground Link: here

Related Issues: #17757

[ghost]

The problem is that Function.prototype is any, and intersecting with any doesn't narrow the type:

declare const x: { a: any } & { a: string };
x.a;

Unfortunately, I don't know a way to write a callable/constructable type that doesn't automatically get prototype: any added to it.

[RyanCavanaugh]

Would need subtraction types or spread types to represent this pattern

[cshaa]

Ah, my bad, evidently I didn't read the docs properly. However it still seems pretty counter-intuitive and broken to me 🤔. From my (probably naïve) point of view, any is the widest type and the intersection of any and an arbitrary type A should always be A. What is the rationale behind the actual implementation? Why doesn't it obey the intuitive set-theory rules?

[ghost]

any isn't just a top type, it's an unsafe top/bottom type. const x: any = 0; and const y: string = x both work -- everything is assignable to any and any is assignable to everything.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.