On Nov 28, 2012, at 1:09 PM, Tom Van Cutsem wrote: > 2012/11/26 Dean Tribble <[email protected]> > On Mon, Nov 26, 2012 at 11:33 AM, Tom Van Cutsem <[email protected]> wrote: > Thanks for spelling out these examples. While they still don't feel like > actual important use cases to support, they give a good flavor of the kinds > of compromises we'd need to make when turning to notification-only proxies. > > I agree. My usual expectation for proxies is to support remote and persistent > objects. While supporting other scenarios is great, usually that's > incidental. Is there a broader list of aspirations for proxies? or is this > just a "all else being equal it would be good if we can do this"? > > Let's talk about aspirations for proxies. It will help us set priorities. > > First, some terminology (originating from CLOS, the "mother of all MOPs" ;-) > CLOS method combinations allow a composer to distinguish between "before", > "after" and "around"-style composition: > - "before"-style wrapping gives you only the ability to get notified before > an operation happens. You can abort, but not change, the result of the > operation. This is what notification-proxies offer. > - "after"-style wrapping allows you to get notified of an operation > after-the-fact. Depending on the API, the "after"-wrapper may or may not get > to see the outcome of the operation, and may or may not change the final > outcome passed on to clients. > - "around"-style wrapping is the most general and allows the composer to > decide if and when to forward, and what result to return. It subsumes > before/after wrapping. This is what direct proxies currently provide. > > As far as I can tell, virtual object abstractions like remote/persistent > objects require "around"-style wrapping, because there's otherwise no > meaningful target to automatically forward to. > > Here's a list of use cases that I frequently have in mind when thinking about > proxies, categorized according to whether the use case requires > before/after/around wrapping: > > Virtual objects, hence "around"-style: > - self-hosting "exotic" objects such as Date, Array (i.e. self-host an > ES5/ES6 environment) > - self-hosting DOM/WebIDL objects such as NodeList -virtualizing a backing store as properties. -supported extended property attributes > > Around-style wrapping (need to be able to change the result of an operation): > - membranes > - higher-order contracts
introducing new inheritance schemes, eg, multiple inheritance > > Before-style wrapping: > - revocable references After-style a "doesNotUnderstand" wrapper -- run the operation, but if the result is undefined check if missing property and if so, call DNU handler > > What else? > > Cheers, > Tom > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss
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