On Tue 30 Apr 2013 10:23, Kevin Gadd <[email protected]> writes:
> Is the reason why you wouldn't want to run finally blocks in generators
> described elsewhere on the list?
I am not sure I understand the question. Certainly you want run finally
blocks in response to normal control flow in a generator:
function* g() {
try {
yield 1;
try { yield 2; } catch (e) { yield e; }
yield 3;
} finally {
yield 4;
}
yield 5;
}
function Sentinel() {}
function Sentinel2() {}
var iter;
iter = g();
assertEquals(1, iter.next());
assertEquals(2, iter.next());
var exn = new Sentinel;
assertEquals(exn, iter.throw(exn));
assertEquals(3, iter.next()); // ***
assertEquals(4, iter.throw(new Sentinel2));
assertThrows(function() { iter.next(); }, Sentinel2);
assertThrows(function() { iter.next(); }, Error);
However. If I understand your question correctly, your question is, if
we just stop after the line marked "***" above, does the "finally {yield
4}" block ever run?
To run finally blocks when a generator object is suspended within the
try{} of a try/finally block is to introduce finalizers into ECMAScript.
So if this is really what you want, then your question is "why is it a
bad idea to add finalizers to ECMAScript". I think these slides from
Hans Boehm fairly describe the situation:
http://www.hpl.hp.com/personal/Hans_Boehm/misc_slides/java_finalizers.pdf
Finalizers can be useful but they are not a great interface, they
introduce concurrency, and they are otherwise not currently part of the
language, and so for example V8's great GC hasn't had to deal with
them, which is a win for web performance. Better to avoid adding them
to the language, especially in this oblique way.
Andy
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