@weswigham you might want to take a look at bluebird since I don't understand why it wasn't invariant before.

Same for baidu, although there I have no idea what changed.

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@sandersn - only in case you have time: Can you elaborate what you mean with "Bluebird is invariant on R now."? I’m familiar with invariants from math, but I’m not sure how they fit to your sentence.

I can’t comment on the changes tobaidu-app, but the rest LGTM. 👍

@lhecker The term comes from variance in type theory. That a type T is invariant on a parameter P means that T<P> can only be assigned to exactly T<P>.

In this example, previously bluebird's Promise<Derived> was assignable to Promise<Base> but is now only assignable to Promise<Derived>. No subclasses or superclasses of Derived will work.

This is simpler, but might break some users of bluebird.

The change is due to microsoft/TypeScript#29817.

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@sandersn Thanks! I'll try to remember the nomenclature this time. 😄

Although I do have to agree with you... That might be pretty bad for Bluebird or even TS in general. Are you (or the original author @weswigham) sure such a change isn't a bit too serious?

I mean the following is broken in the newest nightly, but works using the current release.
IMO this should continue to be legal code... (Edit: I mean this code with Bluebird in particular.)

import Bluebird from "bluebird";

class Base {
    base: string;
}

class Derived extends Base {
    derived: number;
}

// Error on the next line:
//   Type 'Bluebird<Derived>' is not assignable to type 'Bluebird<Base>'.
const promise: Bluebird<Base> = Bluebird.resolve(new Derived);
promise.then(instance => console.log(instance.base));

Either way... If this change does land in a release will it be part of TS 3?

@lhecker Yeah, I think that bluebird should be fixed and that my change to the tests is wrong. I'm not sure whether the fix should be in typescript or in bluebird's definitions.

I'm going to revert the bluebird changes until I can talk to @weswigham about the right fix here.

I just published @types/[email protected] to npm.

I just published @types/[email protected] to npm.