On 13.04.2011 17:38, Kyle Simpson wrote:
See http://wiki.ecmascript.org/doku.php?id=strawman:default_operator
-- the proposal there is ?? and ??= since single ? is ambiguous
after an expression due to conditional expressions (?:).
The "default operator" doesn't address a significant part of what
Dmitry is asking for -- the . in the ?. usage -- which allows the
property access to be expressed only once and used for both the test
and assignment.
let street = user.address?.street
which desugars e.g. into:
street = (typeof user.address != "undefined" && user.address != null)
? user.address.street
: undefined;
Part of what Dmitry asked for, I'd like to see in the plain ?:
operator, and it seems like it would be possible to disambiguate from
a top-down parser perspective. I would like to see the `:` ("else
condition") portion of a ?: expression be optional. For instance:
var a = b ? c; // aka, `var a = b ? c : undefined`
Hm, intuitively the form `a = b ? c` sounds for me as:
a = b ? b : c
Dmitry.
The other (more awkward/obscure looking) way to do this is:
var a;
b && a = c;
The difference between the sytnax sugar I'm asking for and the
"default operator" in the strawman is that ?: (or &&) allows for
separate expressions for the test (`b`) and the success_value (`c`),
whereas ?? requires that the test expression and success_value be the
same expression.
For instance:
var a = (b > 5) ? b : undefined;
In this case, the ?? "default operator" is of no use. But being able
to drop the `: undefined` part, and also avoid using the more awkward
looking && syntax, would certainly be a useful sugar.
--Kyle
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