Existential operator (was: ||= is much needed?)

[Aymeric Vitte]

Coffeescript seems to have some radical behavior (a.b?.c.d.e.f) a bit 
similar to what I suggested (which ok can not be in js)

But the discussion here still does not say how much a.b?() or 
a.b?.call(xxx) is used in coffeescript

Personnaly I was thinking that ?. should more allow to check existence 
rather than both checking and calling it if it exists, difficult to win 
everywhere

Le 19/06/2012 22:35, Allen Wirfs-Brock a écrit :
>
> On Jun 19, 2012, at 12:37 PM, Jeremy Ashkenas wrote:
>
>> On Tue, Jun 19, 2012 at 3:33 PM, Allen Wirfs-Brock 
>> <allen at wirfs-brock.com <mailto:allen at wirfs-brock.com>> wrote:
>>
>>
>>     >  foo.bar?(args) <==>  foo.bar?.call(foo, args)
>>     >  fun?(args) <==>  fun?.call(undefined, args)
>>
>>     How are these equivalent? Won't  fun?.call evaluate to undefined
>>     if fun is undefined and undefined(undefined,args) will throw...
>>
>>
>>  ... check out the compilation:
>>
>> http://coffeescript.org/#try:fun%3F.call(undefined%2C%20args)%0A%0Awindow.method%3F.call(window%2C%20args) 
>> <http://coffeescript.org/#try:fun?.call%28undefined,%20args%29%0A%0Awindow.method?.call%28window,%20args%29>
>
> Ah, interesting...so this is actually close to what I was advocating 
> for this particular case.  However, if I now understand correctly you 
> are saying that
>      fun?.call()
> produces undefined if fun is null/undefined but will throw if fun is 
> defined as:
>    fun = new Object;
> because it doesn't have have "call" property.
>
> Also, it isn't clear to me why the second example 
> (window.method?.call(window, args))  is only guarding for null and not 
> undefined.  Is it only because you guard for undefined on variable 
> references and not on property references?
>
> Basically, I see what the code you generate is doing but the unlying 
> semantics that yields that code is less obvious.
>
>>
>> It doesn't eagerly evaluate to undefined ... the value of the 
>> *entire* expression is undefined if the chain is broken at the 
>> existential operator. That's much of the point of soaks:
>>
>> object.property?.i.can.keep.chaining.in.here.without.throwing.errors.if.property.is.undefined 
>>  ;)
>
> Ah, again.  I don't think Brendan's strawman will produce that result. 
>  The ...?.i is going to get undefined when it does GetValue on the 
> Reference produced for object.property.  Then undefined.can will throw 
> in step 5 of 11.2.1 because the LHS is undefined.  Getting this 
> behavior seems to requires modifying . as well as defining ?.
>
> Allen
>
>
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss

-- 
jCore
Email :  avitte at jcore.fr
Web :    www.jcore.fr
Webble : www.webble.it
Extract Widget Mobile : www.extractwidget.com
BlimpMe! : www.blimpme.com

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20120620/46c98a5a/attachment.html>