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

[Herby Vojčík]

Brendan Eich wrote:
> Allen Wirfs-Brock wrote:
>> yes, that's what I was proposing. I think calls need to be part of the
>> overall discussion for this feature area.
>
> Jeremy is kindly grepping more codebases, but just from CoffeeScript
> (self-hosted) source itself, ?. is 42, ?[ is 7, and ?( is 3 -- so
> 12:2:1. Supports deferring ?( for now given syntax issue, but the
> counter-argument is that we might solve syntax holistically a different
> way. One idea:
>
> foo.?bar instead of foo?.bar
>
> which enables
>
> foo(? args )
>
> instead of
>
> foo?( args )
>
> and implies
>
> foo[? index ]
>
> This is infelicitous compared to putting ? first because it separates
> the ? from the maybe-nully left operand too much, and looks ugly (to
> Spanish readers it looks even more wrong).

Let's allow foo.? to denote "soft foo", so you get:

foo.?.bar	// foo == null ? undefined : foo.bar
foo.?(bar)	// foo == null ? undefined : foo(bar)
foo.?[bar]	// foo == null ? undefined : foo[bar]

but maybe also more esoteric uses, like:

for (let key in foo.?)	// for (let key in (foo == null ? {} : foo))
foo.?		// foo == null ? undefined : foo // sort-of clearing
foo.? = bar	// foo == null ? undefined : (foo = bar)
		// this semantics is logical, just don't know
		// what would be the use case...
foo.?.baz = bar	// foo == null ? undefined : (foo.baz = bar)
		// this is usable
... foo.? ...

Herby

> The other idea mooted:
>
> foo?:( args )
>
> runs into the X ?: Y problem -- that should mean X ? X : Y per GNU C and
> intuition, but the : in the middle of ?:( doesn't mean any such thing.
>
> My super-flammable straw syntax of foo?.(args) has a similarly inapt dot
> in the middle.
>
> Suggestions welcome. If we must get maybe-call in or at least
> future-proof the syntax for it a bit, now is the time.
>
> /be
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