On Oct 11, 2007, at 1:36 PM, Garrett Smith wrote: > On 10/10/07, Brendan Eich <[EMAIL PROTECTED]> wrote: >> On Oct 10, 2007, at 3:53 PM, Garrett Smith wrote: >> if (it is Callable) ... >> > I wonder how host objects will deal with this. > > Will there be a transitive relationship of callable and ()?
For transitivity you need a binary relation. The |is| operator is binary and transitive. The () operator is not binary and not in any general sense transitive. So I'm not sure what you mean here, but moving on: > If an object accepts arguments, it is callable, and if it is callable, > it supports ,call(), right? You mean if (it is Callable) then it.call(thisp, arg1, ..., argN) works? No, because (it is Callable) is true for cases where !(it instanceof Function). If you want to apply or call a non-function callable, use Function.apply(callable, thisp, argArray) or Function.call(callable, thisp, arg1, ...argN). > typeof appendChild; // "object" > appendChild is Callable; // ??? See the ticket I cited, http://bugs.ecmascript.org/ticket/153, where the Callabe structural type is defined as { meta::invoke: * } (or possibly { meta::invoke: Function }). That is, if any object implements the meta-object hook for invocation, it is callable. As shaver notes and ES1-3 put it, this is the [[Call]] meta-method. It is exposed in ES4 as meta::invoke. If some future rev of IE (not retrofitted with ScreamingMonkey :-/) has a callable DOM method appendChild, but (appendChild is Callable) evaluates to false, well, that would be a bug. > In IE, appendChild.call is undefined, yet accepts arguments. It's like > a host function that's bound, internally, to its node. Its thisArg is > always the node; execution context is irrelevant. It's an odd duck. That's not something ES4 will prescribe, but again: use the new-in- ES4 static generic Function.call (or Function.apply) if you need to. > document.all(), document.links(0) are also non-functional, but "do > something" when you use arguments (). That something is not [[call]]. > Opera mimicked this odd behavior with document.all and Mozilla did too > in BackCompat mode. I don't know what "BackCompat mode" means, but we do reflect document.all if a script uses it without object-detecting it, and only in such cases (since many well-written scripts fork based on if (document.all) ... else ... tests and we want to run the else clause). This is all not normatively specified by ES4. It's fodder for a future WHAT-WG or W3C webapi spec on ES4 DOM binding. But we are providing the tools for generalizing callability apart from (it instanceof Function), and we are providing static-generic Function. {apply,call}. These should be enough. > Hosts that create such objects create a deceptive and confusing > interface. It's like "what the heck is this thing?" I agree, and Gecko's DOM takes pains to reflect methods as instances of Function, as far as I know. I believe this came up on a w3c list in the last year, possibly webapi or html-wg. Can someone find the thread? /be _______________________________________________ Es4-discuss mailing list Es4-discuss@mozilla.org https://mail.mozilla.org/listinfo/es4-discuss
