On Wed, Sep 18, 2013 at 11:52 AM, David Bruant <[email protected]> wrote: > Le 17/09/2013 15:36, Jason Orendorff a écrit : >> The performance argument is a non-starter > > Why? (damned! how do I find myself defending invoke while I'm relatively > against it...) > Till Schneidereit's enthusiasm about it and the promised boost for Shumway > suggests that the performance difference is significant to not be a > non-starter.
OK, I'll unpack this. There are two different performance arguments. 1. "Method calls on proxies will be faster with the .invoke hook." I think implementations can optimize this transparently, if it matters. Also, I could be wrong, but I think implementers generally don't want TC39 to help them optimize things by adding extra features. Also, I think this doesn't matter. It's hard to prove a negative, but here's a data point: CPython has been around 22 years now and to this day allocates a new bound-method object for every single method call. Not just proxies. All objects. All methods! Granted, CPython doesn't aspire to JS-like performance—but they do care about speed, and this would be low-hanging fruit for them if it mattered. Unlike the proposal we're talking about, it could be done transparently and would affect **all existing Python code**. Why haven't they done it? A little inline cache. It’d be easy. It just doesn't matter. The most performance-critical stuff won't be able to afford going through a proxy, full stop. Everything else won't care if there's one trap or two. (The occasionally-alleged use cases involving Proxy handlers doing high-latency remote procedure calls seem like a bit of a stretch, given the async world that JS actually inhabits.) 2. Till's use case. Till is translating ActionScript to JavaScript. ActionScript has something like invoke traps: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/utils/Proxy.html From Till's perspective, any AS method call could be a proxy method call. It becomes much easier to translate them to fast JS code if we just add .invoke traps to JS as well. As much as I admire the Shumway project, this isn't a good reason to add a language feature. I think both performance arguments are non-starters, not because I dismiss such arguments out of hand (I don't) but because I looked and they just don't go. -j _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
