On Mon, Nov 19, 2012 at 9:46 PM, Brendan Eich <bren...@mozilla.com> wrote: > Tab Atkins Jr. wrote: >> If we did this, the only reason to continue subclassing Map is to get >> instanceof checks to work. Is this acceptable? > > I think it's either irrelevant (no one tests 'aUrlQuery instanceof Map') or > else a potential problem (cross-frame instanceof).
People *do* perform those checks, though. For example, in a method that accepts either an array or other things, a quick "foo instanceof Array" check is a clear, easy way to check what you've got. It suffers from cross-frame issues, but shrug. Similar checks will proliferate as people write methods that take generic Maps. (On the other hand, they might instead just feature-test for the existence of items(), and then use it as an iterable, in which case this would be a non-issue. Depends on the use-case, I suppose.) > Where I would like to go, if you force me to pick a promising path: > > http://disnetdev.com/contracts.coffee/#duck > http://disnetdev.com/blog/2011/09/05/Duck-Typing-Invariants-In-contracts.coffee/ That's my preferred direction, too, but I suspect that's far off. It doesn't even have a strawman yet, does it? ~TJ _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
