typeof extensibility, building on my Value Objects slides from Thursday's TC39 meeting

Brendan Eich brendan at mozilla.com
Sat Aug 3 20:29:05 PDT 2013


Claude Pache wrote:
> Le 4 août 2013 à 01:34, Brendan Eich<brendan at mozilla.com>  a écrit :
>
>> Claude Pache wrote:
>>> Fixing `typeof` of old (null) and new value types would be a solution, but I'm rather definitely considering something like the defunct `Object.isObject()`. (As a side-note, I suggest `typeof uint64(0) === "number"` rather than `=== "object"` by default.)
>> That will make for bugs where number (double) loses precision, and other bugs where int64 carries too many bits of significand. It also violates the two-way
>>
>> (typeof x == typeof y&&  x == y)<=>  (x === y)
>>
>> which we want for 0 == 0L, 1 == 1L, etc. (and consider other value types; this goes back to our work with Sam Ruby for IBM on decimal in 2008-9).
>
> So, if I understand well, this mandates that int64 and float32 (for example) should have different typeof values, ergo both "object" (as in [1]) and "number" (as I proposed) are equally bad answers, and the most reasonable default value of typeof for int64 would be "int64"?

Yes, this was the consensus at the meeting (not reflected in 
http://oksoclap.com/p/64ETm1ontG -- my fault -- but the slides are up to 
date and capture all the action items: 
http://www.slideshare.net/BrendanEich/value-objects).

> [1] http://wiki.ecmascript.org/doku.php?id=strawman:value_objects

That's out of date and I'm going to edit it for the next TC39 meeting. 
Thanks (to everyone who replied) for being a good sounding board here on 
es-discuss, in pre-strawman stage ;-).

/be


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