July 31 2014 TC39 Meeting Notes

Rick Waldron waldron.rick at gmail.com
Tue Aug 5 09:31:46 PDT 2014

# July 31 2014 Meeting Notes

Brian Terlson (BT), Dmitry Lomov (DL), Waldemar Horwat (WH), Allen
Wirfs-Brock (AWB), John Neumann (JN), Rick Waldron (RW), Eric Ferraiuolo
(EF), Jafar Husain (JH), Jeff Morrison (JM), Mark Honenberg (MH), Caridy
Patino (CP), Sebastian Markbage (SM), Istvan Sebestyen (IS), Erik Arvidsson
(EA), Brendan Eich (BE), Mark Miller (MM), Sam Tobin-Hochstadt (STH),
Domenic Denicola (DD), Peter Jensen (PJ), John McCutchan (JMC), Paul
Leathers (PL), Eric Toth (ET), Abhijith Chatra (AC), Jaswanth Sreeram (JS),
Yehuda Katz (YK), Dave Herman (DH), Brendan Eich (BE), Ben Newman (BN)

## Notes from secretariat

IS: ES6 delay accepted, but please don't delay this again.

- TC52 working in a similar way and process to TC39's ES7 approach:
Frequent releases of incremental versions of standards. They also use the
same kind of RF policy.
- TC52 is looking at how TC39 is proceeding
- TC52 are more polite

IETF and Internet Architecture Board liaison.
- JSON work and looking for liason. We published Ecma-404 and they are
publishing their standard and have asked for review/comment. Need to
nominate someone as liaison.

ITU liaison.
- Using in JSON for communication standard

Meteor group has joined Ecma

JN: Recommend putting out a call for liaisons, including the information
you have. List roles and expectations, we'll put it on the next meeting
agenda to establish appointment.

AWB: There has been a notification for these roles.

JN: Is anyone here prepared to volunteer now? Or at the next meeting. Need
someone to at least collect the communications out of those organizations.

#### Conclusion/Resolution

- John Neumann to stand in as liaison

## 9.1-8 Date and place of the next meeting(s)

JN: Need to fill in the venues.

DH: January 27-29, 2015 at Mozilla (Downtown SF, CA)

EF: March 24-26 2015 at Yahoo (Sunnyvale, CA)

JM: May 27-29 2015 at Facebook (Menlo Park, CA)

ET: November 17-19 at PayPal (San Jose, CA)

RW/YK: Will decide on Sept. 2015

#### Conclusion/Resolution

- John Neumann will update the agenda and schedule.

## 4.4 Follow up: Instantiation Reform (@@create)

JM: Found cases where we set up state before calling super. I'm convinced
that there are sufficient workarounds (via calling <<SuperClass>>.call() in
the legacy style).

https://gist.github.com/jeffmo/bf30e7154ab3c894b740 -- "#_Before.js" is an
example of a pattern that exists now, "#_After.js" is an example of how one
might fix this pattern

JM: (gives examples that amount to two step initialization)

WH: C++ doesn't allow this kind of bottom-up construction (can't initialize
a subclass instance before the superclass instance is initialized), and use
cases like this arise once in a while. The usual workaround is to pass
through Options objects.

JM: (example of type ahead classes in FB code base -- see 2_Before.js and
3_Before.js in the above gist)

AWB: (draws model of two phase allocation)

YK: The problem is allocatuion vs. initialization, in your model mutates
before calling super.
- Need to make sure the allocation has happened before you get into the
- It looks like the only way to fix this is to have "two constructors",
which we can't do

SB: We don't want to support this pattern, but there is nothing to stop
user code from doing this.

AWB: "Fragile Base Class Problem"
- Start at derived class
- super'ed up to base class
- Base class invokes method that's defined on the subclass
- The problem is that the object isn't set up yet.

This is a bug.

AWB/YK: (Further discussion of how to avoid this pattern)

JM: Special case refactoring in subclasses isn't trivial.
- Both direction have down side:
  - TDZ approach negates certain cases
  - Non-TDZ approach allows for decoupling of allocation/instantiation

YK: Lifting the TDZ doesn't solve the problem. It happens to work in this
case because the base class doesn't allocate.

AWB: There is way to do this in the new design, use the construct method

SM: Foresee a tooling solution (e.g. linting for properly placed calls to

AWB: Will always come to a place where a problem can't be solved with your
existing inheritance model and you'll simply need to refactor. It's not
that inheritance has failed, just that the class heirarchy needs to be

JM/SM: Refactoring is the correct approach, but it can be idealistic in
some scenarios. Imagine a TypeaheadBase class that has been subclassed 100s
of times. It's not until the 101th time that you realize you need to
refactor the base class (and, thus, all pre-existing subclasses)

Discussion about subclasses that require two phase construction (with
instance side initialization methods)

Mixed discussion about allocation phases.

MM: Do we have consensus on the instantiation reform we agreed to


[JM agrees on the grounds that there are at least legacy style workarounds
for that 101th subclass and the rest of the patterns he found a la

YK: will not be ok with this solution if it switches on the instantiation
of the constructor

...Need help covering this...

WH: I insisted on having a syntactic switch for function-vs-generator
rather than switching on the presence of a yield. The reason was that
functions and generators are radically different and it makes sense for a
trivial generator to have no yields. In this case I'd mildly prefer to have
a syntactic switch as well, but it's not as crucial because I haven't seen
any good examples of where apparently problem-free code would unexpectedly
go wrong. If you don't call the superclass constructor, you'll miss out on
superclass initialization, which would be a problem even if the presence of
a super call didn't statically switch modes, so the mode switch hasn't
created a problem where there wasn't one. Inserting or deleting an "if
(false) super()" does change things, but I don't see why one would be
likely to do that. [I suppose that you could stylistically mark inheriting
constructors whose super() calls are deeply buried with an "if (false)
super()" at the top :).]

MM: I agree there is a smell with super; would I adopt syntactic marking? I
want to see them first.

WH: On the fence, suppose we do this, what if you call super in a method
not marked? What does that do?

DH: It's ok for class body to have more syntactic distinctions than outside
functions acting as constructor

AWB: You could imagine that I have a splat that indicates "I do not want
allocation for this class"

#### Conclusion/Resolution

- Agreement to MM proposal: Allen to be the champion and work out the
details remaining

## ES7 Items?

DH: We should focus on ES6 items, we have limited time in face to face.

DD: I don't think we should de-prioritize ES7, given the train model.

AWB: We have no choice but to prioritize ES6

## 5.7 Array.prototype.contains

(Domenic Denicola)

Follow up from RW's Stage 0 in

DD: Presents: https://github.com/domenic/Array.prototype.contains/

DH/RW: Parity with String

RW: Most arguments were noise and Domenic's proposal addresses them all.

AWB: One of the previous objections: string.contains is looking for a
substring, not an element.

EA: Same thing with indexOf

JM: Can you give an example where this is a problem?

MM: Consistently inconsistent parity with indexOf

#### Conclusion/Resolution

- Advance to Stage 1

DD: Would like to do Stage 2 and 3 asynchronously due to the simplicitly of
this proposal.

AWB: I'd like the process to be respected.

MM: If Stage 2, 3, and 4 are complete by next meeting, then we can advance
to Stage 4.

Discussion re: the ES7 process.

AWB: Concerns about lack of review that results in more work later in the

MM: We don't have a mechanism to come to consensus outside of these
meetings. These meetings _are_ the time that we're able to work on these
issues. This is my allocated time

## 5.1 Math.TAU

(Brendan Eich, Rick Waldron)


BE: Math.TAU = 2PI

WH: OK, but only if it's called Math.τ :-)

MM: Opposed: one letter shorter, not well known, not well taught. PI is
known, taught and ubiquitous.

#### Conclusion/Resolution

- Rejected.

## Exponentiations operator

(Rick Waldron)


RW: All other languages have it. Why can't we?

RW: Needs hihger precedence than multiplication

MM: Right associative?

RW: Yes, same as all other languages.

BE: **?

MM: Want to make sure that it does the same as the built in %MathPow% and
not not any overload.

RW: Confirm

DH: Wants to point out that adding syntax does have a cost. But thinks it
is fine and there is a lot of precedent.

#### Conclusion/Resolution

- Approved for Stage 0, in 6 minutes.

## Precision of Math trig functions

(Dave Herman)

DH: V8 made the result less exact in the name of performance. Are we going
to have a "race to the bottom"?

DH: People are now starting to implement these algorithms in js since they
cannot depend on the built ins.

DL: Java lies. Implementations do not follow the Java rules.

WH: Looked at the posted data and found it pretty compelling that the
status quo free-for-all is not good. Some functions that should be
monotonous aren't. Some results are significantly off.

WH: fdlibm should be the lower bar for precision. It almost always gets
things exact or within 1 ulp.

DH: Talked to an expert (Dan Gohman) and he offered to come to this
meeting; I told him he could wait and see how the conversation goes and
maybe come in the future.

WH, DL: We need to invite experts to get the right answer to this.

MM: When doing the sputnik tests we just looked at the results and based
the precision on what browsers did when the tests were written.

AWB: We need a champion.

DL: V8 is planning to fix this and make the results more accurate.

#### Conclusion/Resolution

- Need to bring in experts.
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