On Aug 21, 2008, at 4:05 PM, David-Sarah Hopwood wrote:
> Brendan Eich wrote:
>> The maddening mix of dynamic scope (the hopeless global top-level,
>> with, eval) and lexical scope [...]
>
> 'with' is lexically scoped.
> <http://groups.google.com/group/google-caja-discuss/browse_thread/
> thread/edc12e29e2cfba9f/c2ea493e83a6bf1f?lnk=gst#c2ea493e83a6bf1f>
There, you wrote
"The first example illustrates (but does not prove) that 'with' actually
provides lexical scoping, *provided* that all free identifiers in the
scope of the 'with' exist as properties of the supplied scope object. "
The *provided* is not guaranteed by 'with', so if it's not satisfied,
then by your own argument 'with' does not provide lexical scoping.
Perhaps you meant to write "'with' may but not must be lexically
scoped"?
Consider this counter-example:
var opt_A = false, opt_B = 0, opt_C = ""; // defaults
function setOptions(opts) {
with (opts) {
if (opt_A) setOptionA(true);
if (opt_B) setOptionB(opt_B);
if (opt_C) setOptionC(opt_C);
}
}
setOptions({opt_A: true, opt_C: "hi"});
setOptions({opt_B: 42, opt_C: "bye"});
I'm not recommending this kind of code, but IIRC Lars Hansen pointed
out the pattern, based on sightings in the wild.
Is this "dynamic scope" in the classical sense? No, but it smells as
bad and has similar undesirable properties ;-).
These old docs may be worth a read:
http://wiki.ecmascript.org/doku.php?id=clarification:lexical_scope
http://wiki.ecmascript.org/doku.php?id=proposals:reformed_with
> (Please don't interpret this as a defence of 'with'.)
No worries.
/be
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