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

[Jeremy Ashkenas]

On Tue, Jun 19, 2012 at 3:33 PM, Allen Wirfs-Brock <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)

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
 ;)
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