On 10/11/07, Brendan Eich <[EMAIL PROTECTED]> wrote: > 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). > So these are equivalent?
aNonFunctionCallableObj() Function.call( aNonFunctionCallableObj ) > > 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. > If an object is invokable with arguments (), but not a Callable, it's impossible to type check. IE's call-like operation on with () is not [[call]]. Microsoft often says that it is necessary to retain backwards compatibility. I would hope they would Mozilla has this weird function-like thing, too, (only with document.all, which is not used much anymore) > > 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). > document.compatMode "CSS1Compat" -- standards mode "BackCompat" - quirks mode BackCompat supports document.all > 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. > Mozilla really made document.all look like IE's weird collection-that-can-be-invoked-with-(). document.all.call(document, 0) * Non-standard document.all property was used. Use W3C standard document.getElementById() instead. * [Break on this error] undefined javascript: with ... (line 1) document.all.call is not a function Yikes! > I believe this came up on a w3c list in the last year, possibly > webapi or html-wg. Can someone find the thread? > I'll look for that. Garrett > /be > > -- Programming is a collaborative art. _______________________________________________ Es4-discuss mailing list Es4-discuss@mozilla.org https://mail.mozilla.org/listinfo/es4-discuss
