On Mon, Aug 29, 2011 at 7:43 AM, Tom Van Cutsem <[email protected]> wrote:
> (changed subject to fork off discussion on function proxies) > > 2011/8/29 Allen Wirfs-Brock <[email protected]> > >> On Aug 27, 2011, at 6:12 AM, Andreas Rossberg wrote: >> > True, and actually, there are more issues with length & function >> > proxies. I don't have my notes with me right now, but for example, it >> > is not clear at all what length Function.prototype.bind should set >> > when called on a function proxy. 0? 1? Should it try to get the length >> > property from the proxy and subtract N? What if length is not defined >> > on the proxy, or not a (natural) number? >> >> The ES5.1 spec. defines how how bind determines the length for the >> function it creates based upon the length property of the target function. >> I would expect the same rules would apply when the target is a function >> proxy. > > > I see two options here: > a) either query the function proxy for its "length" property via its "get" > trap, and convert the result using ToInteger, introducing a new error case > if the conversion fails. > b) or determine "length" based on the function proxy's call trap (which is > presumably a non-proxy function. If it is a function proxy itself, recurse) > > The spec currently uses the wording: "Let L be the length property of > Target ..." (ES5.1 section 15.3.4.5) > If that is not equivalent to "Let L be the result of calling the [[Get]] > internal method of Target with argument "length"", then option b) seems > better. > > There is precedent for using the call trap as a substitute for the function > proxy: Function.prototype.toString.call(aFunctionProxy) will also use the > call trap's toString representation rather than trapping the handler. > I don't have any strong preference regarding #a vs #b. However, I don't think Function.prototype.toString.call(aFunctionProxy) is a relevant precedent. For .length, we have the choice of #a or #b. For ...toString.call, what other option could there be besides the choice we made? -- Cheers, --MarkM
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