Existential operator (was: ||= is much needed?)
brendan at mozilla.org
Sun Jun 17 22:11:06 PDT 2012
Sorry, meant to start a new thread for:
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.
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
>> - 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
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