Hi, I'd like to discuss forwarding proxy patterns. I'll call "full handler" a handler with all current traps and "own handler" a handler with just the own properties layer traps. The current forwarding proxy pattern is: --- var p = Proxy.create(fullForwardingHandler(target)); --- Any interaction with p is delegated to target. To visualize the prototype chain, we have: ------- p --> null target --> Object.getPrototypeOf(target) --> ... --> null ------- Notably, all prototype-climbing calls are delegated to the target prototype chain regardless of what p prototype is (I'll get back to that later)
We have seen a limitation of providing a full forwarding handler systematically (http://wiki.ecmascript.org/doku.php?id=strawman:derived_traps_forwarding_handler). Regardless of what is decided on the strawman, some people may want to only provide own traps. One "lighter" way to provide the same forwarding handler would be to do: var p = Proxy.create(ownForwardingHandler(target), Object.getPrototypeOf(target)); Which would visualize as: --- p ----------- \ target --> Object.getPrototypeOf(target) --> ... --> null --- So at the own layer, p and target act exactly the same. They also act the same when it comes to inheritance but not thanks to prototype climbing traps. They do so because they natively delegate to the same prototype object and use the default trap behavior. So, they are also consistent with instanceof and Object.getPrototypeOf (and the prototype is correct when the proxy is fixed which is a consistent side-effect. This doesn't happen with current full forwarding and null prototype). Ok, now that we are able to be in sync only at the own layer, one interesting pattern is the following --- p --> Object.getPrototypeOf(p) --> ... --> null target --> Object.getPrototypeOf(target) --> ... --> null --- with p and target in sync at the own layer. For all own operations, p would forward to target, however, for all proto-climbing operations p would use its own properties. Actually, this works without any effort with the OwnForwardingHandler since its default derived traps delegate to the correct prototype by default. This pattern could be used for a new prototype inheritance pattern where o1 could inherit from p, o2 from target. They would both feel they inherit from the same object (since p and target are in sync) while, one step further inheriting from completely different objects. All of this is just a discussion on the forwarding proxy pattern. But I think it was worth pointing the potential limitations of how this pattern is currently presented (limitations which are different from the one previously noticed which led to strawman:derived_traps_forwarding_handler). David _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
