On May 23, 2011, at 10:41 AM, Brendan Eich wrote:
> On May 23, 2011, at 10:03 AM, Alex Russell wrote:
>
>>> (A) the boilerplate needed to set up a sub-prototype object with correct
>>> constructor property, and
>>>
>>> (B) the pain of doing correct super calls by hand.
>>
>> I hope we can add the hazards of incorrectly adding mutable state to a
>> prototype and not an instance to this list. I.e., many people get this wrong:
>>
>> function C(){
>> // should include:
>> // this._list = [];
>> }
>> C.prototype = {
>> _list: [],
>> addToList: function(item) {
>> this._list.push(item); // logic error!
>> // side-effects here
>> }
>> };
>>
>> Allen and I have discussed this before, so it's not a surprise, but I'm
>> worried that some proposals might omit fixing this on their todo list.
>
> That's a good (C) but I do not see it addressed. Indeed Bob Nystrom counted
> occurrences in one codebase and found default property values set in class
> prototypes.
>
> Your point seems to be that mutable (object) default values are a mistake,
> and I tend to agree. But how to exclude this option? Just adding sugar won't
> prevent such mistakes, indeed it could make the mistake more likely,
> depending on ergonomics and more imponderable user factors.
>
> Where and how does the current proposal address (C)?
I don't think it does explicitly. The repair would be a hidden __init__ sort of
method that does property default initialization on instances before the
user-provided constructor is called.
In talking with Peter and Arv, it sounded like they thought this was the sort
of thing we'd be able to hammer out once the strawman reaches proposal (and I
agreed), although I do think it's worth calling out explicitly in the strawman
too.
Regards
> /be
>
>
>>
>>> Can we agree that these are problems to be solved, if not by classes then
>>> by other APIs or special forms?
>>>
>>> /be
>>>
>>> _______________________________________________
>>> es-discuss mailing list
>>> [email protected]
>>> https://mail.mozilla.org/listinfo/es-discuss
>>
>> --
>> Alex Russell
>> [email protected]
>> [email protected]
>> [email protected] BE03 E88D EABB 2116 CC49 8259 CF78 E242 59C3 9723
>>
>> _______________________________________________
>> es-discuss mailing list
>> [email protected]
>> https://mail.mozilla.org/listinfo/es-discuss
>
--
Alex Russell
[email protected]
[email protected]
[email protected] BE03 E88D EABB 2116 CC49 8259 CF78 E242 59C3 9723
_______________________________________________
es-discuss mailing list
[email protected]
https://mail.mozilla.org/listinfo/es-discuss
