Kevin Smith wrote:
I raised this problem-case, so I want to point out that we could
take other courses:
* Reckon that labels are rare and this won't bite, so let it
stand, just as
a = b
(c)
is a hazard today -- and one that bites much more.
* Don't allow suffix-? to be followed by a newline.
Leaving aside ASI for a moment, there are other issues:
let v = obj?+(0+1+2+3+4+5+6+7+8+9+...+n):null;
We don't know whether this is a conditional expression or not until we
get to the ":" an arbitrary distance away from the "?".
Yes, this is a good point if obj? could be an expression on the left of
binary +. The same problem arises with - / [ and ( of course -- just as
with lack-of-ASI.
We might be able to use another cover grammar approach here, but is it
worth it?
We'd rather use a lookahead restriction forbidding the token after ?
from being in {+,-,/,[,(} -- and possibly from being a LineTerminator,
although that seems silly to me on reflection.
Apart from deviating from the cowpath (CoffeeScript), prefix-? is
equivalent to suffix-? as I argued in reply to Herby. We'd want to
support
let ?{p: v} = o;
let v = ?o.p;
to handle the case of undefined or null 'o', of course, in which
case v would be initialized to undefined.
Would we? This is something a little different than "irrefutable
property get". Thinking...
The suffix-? operator works on identifier expressions too. Those happen
to irrefutably throw just fine (throw ReferenceError) in JS, unlike
MemberExpressions such as foo.bar where !('bar' in foo).
/be
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