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

[Hemanth H.M]

As there is no keyword as 'or' so far, does something like *x = x.value or
5 *sound better?

On Tue, Jun 19, 2012 at 3:00 PM, David Bruant <bruant.d at gmail.com> wrote:

> What about a more generic operator that would be able to silently absorb
> any error?
>
>    let greedy = obj.hints?.greedy;
>
> would become:
>
>    let greedy = silent obj.hints.greedy;
>
> The semantic would be exactly the same.
> The syntax is up to debate. Specifically, it would be nice to be able to
> silence a part of an expression.
> What about a 'try' without a catch?
>
>    let greedy = try obj.hints.greedy
>    let greedy = try{ obj.hints.greedy } || 22;
>
> This is currently forbidden (I think for 2 reasons, one being that a try
> must be followed by a catch or finally and the other that try/catch cannot
> be used as expressions)
>
> This idea is partly inspired by typeof which silences ReferenceErrors,
> which I see as a feature YMMV.
> It is also intended to make programs potentially more robust more easily.
> For instance, JSON.stringify can throw errors in the rare case of cyclic
> references. But very few people know that. To make a robust program using
> JSON.stringify, one would just need to turn:
>
>    let s = JSON.stringify(o)
>
> into
>
>    let s = try{ JSON.stringify(o) } || DEFAULT_VALUE;
>
> instead of the current:
>
>    let s;
>    try{
>        s = JSON.stringify(o)
>    }
>    catch(e){
>        // I don't care about the error anyway
>        s = DEFAULT_VALUE;
>    }
>
> David
>
>
> Le 18/06/2012 07:11, Brendan Eich a écrit :
>
>> Sorry, meant to start a new thread for:
>>
>>
>> http://wiki.ecmascript.org/**doku.php?id=strawman:**existential_operator<http://wiki.ecmascript.org/doku.php?id=strawman:existential_operator>
>>
>> As the Syntax section hints, we can't also adopt CoffeeScript's ?(
>> variant, which enables foo.bar?(args, go, here).baz and the like. The C
>> syntax heritage prevails.
>>
>> /be
>>
>> Brendan Eich wrote:
>>
>>> David Herman wrote:
>>>
>>>> On Jun 15, 2012, at 5:57 PM, satyr wrote:
>>>>
>>>>  On Sat, Jun 16, 2012 at 4:33 AM, David Herman <dherman at mozilla.com<mailto:
>>>>> dherman at mozilla.com>> wrote:
>>>>>
>>>>>    As for null, I can see how there's confusion about whether to use
>>>>>    null vs undefined, and so I can see why CoffeeScript would just
>>>>>    try to blur the distinction between them.
>>>>>
>>>>>
>>>>> Not just for blurring. Rejecting `null` is essential for
>>>>> CoffeeScript's "existence" due to `?.`, the soak/safe access operator.
>>>>>
>>>>
>>>> I think you could make a case for ?. defaulting for both but ??
>>>> defaulting only undefined. The case goes something like this:
>>>>
>>>> - The purpose of ?? is to provide a default value when no value was
>>>> provided. The way to say "no value" in JavaScript is undefined.
>>>>
>>>> - The purpose of ?. is to fail soft when doing a property lookup. Both
>>>> null and undefined throw when doing a property lookup.
>>>>
>>>
>>> Agreed. This is one choice, it's plausible because of the distinction
>>> between defaulting (which requires intentional passing of a "please
>>> default" sentinel value, or not passing a trailing actual argument) and
>>> soaking up null-or-undefined.
>>>
>>> Yes, we could make ?? and ??= do the same for null as for undefined. I'm
>>> not sure that's the right choice, but it's a choice. For foo.bar?.baz,
>>> though, the clearer choice is to avoid throwing, which means evaluating to
>>> undefined if foo.bar is missing (evaluates to undefined) *or* has a value
>>> not coercible to object type (null or undefined). See
>>>
>>> http://wiki.ecmascript.org/**doku.php?id=strawman:**existential_operator<http://wiki.ecmascript.org/doku.php?id=strawman:existential_operator>
>>>
>>> /be
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-- 
*'I am what I am because of who we all are'*
h3manth.com <http://www.h3manth.com>
*-- Hemanth HM *
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