ES2015 Classes and inheritance

[heywiki]

Are there any plans in the near future to implement classes and inheritance in Rhino? And other OO related features described here: https://medium.com/ecmascript-2015/es6-classes-and-inheritance-607804080906

[gbrail]

Class support would be great. It's mainly a case of digging into the parser and syntax tree and making all that work. It's not a easy job though, which is why I don't think anyone has tackled it yet. It's a great project for an ambitous volunteer though.

[p-bakker]

Note that while this case is in milestore ES2015, to date there's a pletora of additional proposals that have made it into the ECMAScript standard that we should also consider when picking case up.

There are currently no stand-alone issues registered for Rhino for all these followup proposals, as they all depend on the initial Class implementation.

Browse https://github.com/tc39/proposals/blob/master/finished-proposals.md for an idea of the followup proposals, like https://github.com/tc39/proposal-class-static-block or https://github.com/tc39/proposal-private-fields-in-in, just to name a few

[p-bakker]

something to keep in the back of our minds when implementing Classes: ability to extend Java classes and syntax suger

Note that at the time of writting, GraalJS doesn't support extending Java classes: oracle/graaljs#32 (comment)

[p-bakker]

Some details on the @@Species/Symbols.species behavior when it comes to subclassing built-ins: https://github.com/tc39/proposal-rm-builtin-subclassing

[gbrail]

This is a big hole in our language support today, IMO. I have struggled off and on to start on this but haven't found the time to really dig in.

Since there are a few of you working on the project now who have been able to really dig in to the parser and IR in detail, perhaps someone could take a crack at this...

I started experimenting with doing this solely as a "transformer" in the parse / compile pipeline, but I found that it wasn't all that helpful really, and I think that we're likely to require at least some new runtime support if we want to get everything right.

[andreabergia]

As a first step, me and @0xe are working on implementing super outside of classes (it relies on prototype).
We expect it's gonna take at least a couple more weeks, but we're making good progress. The temporary branch is here, if you're interested, but the commit history (and the code) are a bit of a mess right now, which is we're not even opening a draft PR yet 🙂 https://github.com/andreabergia/rhino/tree/super-objects-no-class