I've done a little engine work, and inline caches work by inline type maps based on the callee site. This *can* be used to reconstruct values + receivers, but only when the value is constant. It is not sufficient to ensure identity remains the same, and engines would still need a weak map to link methods to instances (as opposed to prototypes).
It's worth noting not even Java or Ruby offers this - their method references/objects (like our bound functions) are *not* memoized - they're linked to classes, not instances. Python is the exception here in auto-binding instance methods, not the norm. On Mon, Mar 11, 2019 at 15:37 Bergi <[email protected]> wrote: > Hi John! > > I think the js run-time already has that information at hand, so as > > long as we don't implement this as pure syntactical sugar, there would > > not be a need to keep an extra reference to anything, because it would > > be already there. The run-time will know which instance the invoked > > method belongs to. > > Well no, you're wrong here: the runtime does not have this information > at hand. In your example (simplified) > ``` > var reqManager = new RequestManager(); > function addEventListener(f) { > console.log(f); > f(event); > } > addEventListener(reqManager.responseHandler); > ``` > the `addEventListener` function will not know that the function `f` you > passed was a method of the `reqManager` instance. It cannot distinguish > that call from > ``` > addEventListener(RequestManager.prototype.responseHandler); > ``` > or > ``` > var g = otherReqManager.responseHandler; > addEventListener(g); > ``` > > It is exactly the same function that is passed in all three cases. There > is no instance bound to `f`, and `f(event)` will not invoke it as a > method (with a receiver/`this` value). > > Best regards, > Bergi > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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