Le 02/12/2012 17:27, Tom Van Cutsem a écrit :
2012/11/28 David Bruant <[email protected] <mailto:[email protected]>>
I don't understand why a unique token per trap invocation would
be necessary.
I still don't understand this point.
I've gone spelunking. I've found:
* the wiki page [1] (reflecting July meeting) which mentions that
returning undefined would express "I don't know the private name,
please forward"
* Confirmed on July 31st [2].
* Introduction of the idea of putting the verification of known
names somewhere else than for each trap return [3]. Some
discussion in between about this idea. Introduction of the idea of
adding a third argument [4] after which I think stops all
discussions about returning something in traps to prove knowledge
of a private name or forwarding when not knowing.
I don't remember the point about a token per trap invocation and I
haven't been able to find it (but I haven't read everything).
In any case, for "throw ForwardToTarget", I don't see why it would
be necessary. It seems it would work unambiguously with
meta-handlers, with target-as-a-proxy or with
manipulate-any-other-proxy-inside-a-trap (which target-as-a-proxy
is an instance of).
I think throwing a special token, as is done with StopIteration would
probably work in practice (little risk of confusing it with a
legitimately returned value). However, it does require every trap
invocation to be wrapped in a try-catch block to potentially catch
that error.
Yes and no. The "try-catch" is inside the engine, very much like for
StorIteration in for-of loops.
In case current implementations had performance drawbacks, I feel they
could special-case when they know they are calling a function in the
context of a particular protocol (iterator or proxy trap for instance).
Maybe I'm too influenced by the JVM, but my understanding is that
wrapping every call to a trap with a try-catch block won't be free.
The more interesting question is whether it would be significantly
cheaper than 'returning a value+invariant checks' because that's the
reason I suggested the addition of "throw ForwardToTarget".
Perhaps implementors can comment.
Yep.
David
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