Herby Vojčík wrote:
Brendan Eich wrote:
Herby Vojčík wrote:
That is, these are identical, except the syntax:
r = o.p.q {p: {q: r}} = o
r = o.?p.q {?p: {q: r}} = o
P=o.p; Q=o.?q {p: P, ?q: Q} = o
Here I part company only on syntax:
r = o?.p.q {p?: {q: r}} = o
P=o.p; Q=o?.q {p: P, q?: Q} = o
And of course, the short-hand works:
p=o.p; q=o?.q {p, q?} = o
Oh, now that I see details, I do not like the syntax, because the
symmetry of use of ? vanished.
Compare:
r = o.?p.q {?p: {q: r}} = o // in both forms, "?p"
vs,
r = o?.p.q {p?: {q: r}} = o // 1st: "o?"; 2nd: "p?"
You're right, and in CoffeeScript o?.p tolerates null or undefined o.
Given eo.cs:
o = null
o?.p
o?.p.q
`coffee -p eo.cs` shows
(function() {
var o;
o = null;
if (o != null) {
o.p;
}
if (o != null) {
o.p.q;
}
}).call(this);
So the ? in ?. really does modify its left operand.
It would be bad to diverge from CoffeeScript by standardizing some other
?. in ES7.
ISTM your equivalence was slightly broken -- but we can fix it:
r = o.p?.q <==> {p?: {q: r}} = o
To tolerate o = null and o = undefined (which is not what o.p?.q does),
the equivalence would be:
r = o?.p.q <==> {p: {q: r}}? = o
I think this all works and makes sense. On the left, ? goes after the
leading object or would-be object, denoted o. On the right, ? goes after
the outermost object pattern.
Suffix vs. prefix should be an independent design decision, because ? as
prefix should work the same on both sides, ergo, transposing around the
operand to make ? a suffix should work the same on both sides.
/be
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