PS Correction: it's actually a non-standard extension that regexps are callable in SpiderMonkey. So the invariant is that the only callable non-host objects are descendants of Function, or possibly host objects. This doesn't change my overall point, though.
On Feb 23, 2011, at 2:26 PM, David Herman wrote: > I've been working on a prototype implementation of the binary data spec in > pure JS (implemented via typed arrays) and I've been bitten by the lack of a > standard mechanism for subclassing Function. > > I'm using proxies for the implementation, and Proxy.createFunction doesn't > let me specify a custom prototype. Now, I can understand that this preserves > the existing property of the language that the only callable things are > either regexps or descendants of Function. But we could extend the proxy API > to allow custom functions with user-specified prototypes and still preserve > this property: > > Proxy.createFunction(handler, callTrap[, constructTrap[, proto]]) > > The proto argument would default to the original value of Function.prototype > [1]. But if the user provides a prototype, the library could enforce that > proto instanceof Function [2]. This way we would preserve the invariant that > for any callable value v, either v is a regexp or (typeof v === "function" && > v instanceof Function). > > Maciej has also suggested a Function.create(...) API for more lightweight > creation of function subtypes. This would strengthen the argument for > allowing Proxy.createFunction to specify a prototype, since > Proxy.createFunction() ought to be able to do anything Function.create() can > do. > > I'm curious to know if there are reasons I've missed why > Proxy.createFunction() doesn't support a custom prototype. It seems to me > like a nice additional expressiveness without any great loss of language > invariants. But I may have missed something. > > Thanks, > Dave > > [1] In the face of multiple globals, this would be the Function associated > with the same global as Proxy. (BTW, I intend to work with Andreas on > speccing out multiple globals.) > > [2] Again, the Function associated with the same global as Proxy. > > _______________________________________________ > es-discuss mailing list > es-discuss@mozilla.org > https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
