On Tuesday, November 20, 2012 at 5:25 PM, Tab Atkins Jr. wrote:
> On Tue, Nov 20, 2012 at 2:06 PM, Rick Waldron <[email protected]> wrote: > > On Tue, Nov 20, 2012 at 3:08 PM, Tab Atkins Jr. <[email protected]> > > wrote: > > > Nope, that's not good enough. For example, you have to do input > > > cleanup (replacing lone surrogates with U+FFFD, escaping &, etc.) > > > which affects whether two keys are "the same". This affects set()'s > > > replacing behavior, and add()'s coalescing behavior. Heck, even > > > without extra cleanup, just the fact that it requires string keys > > > means you need to eagerly preserve the invariant - foo.set([1,2], > > > 'bar') and foo.set('1,2', 'bar') should both set the same key. So, > > > the stringifying must be eager. Additionally, you *must* override the > > > plain method anyway, since (if the URLQuery is attached to a URL), it > > > synchronously adjusts the underlying URL as well. > > > > > > However, if you do a normal subclass, then people can do silly things > > > like "Map.prototype.set(query, key, val);", which would skip > > > URLQuery's own set() method, avoiding the invariant preservation and > > > the URL manipulation. > > > > > > We could avoid these problems by only "subclassing" in the sense that > > > URLQuery.prototype = new Map(); (or Object.create(Map.prototype)), > > > but not invoking the Map constructor and actually storing data in a > > > closure-hidden internal Map, so instanceof would work but using Map's > > > own methods wouldn't. > > > > > > > > > > > class URLQuery extends Map { > > constructor(url) { > > // parse the url into a "map", for now > > // just pretend this is the result of parsing > > // the url: > > let parsed = [ ["a", "alpha"], ["b", "beta"] ]; > > super(parsed); > > } > > getAll() { > > // ... implementation details... > > } > > } > > > > let query = new URLQuery("http://example.com";); > > I'm not sure why you're suggesting this. Deferring to Map's built-ins > for get(), etc. breaks the basic functionality of the object, as I > explained in the quoted section immediately above your response. ^_^ > > I was illustrating the ES6 way to subclass built-ins that result in correctly "inherited" semantics (eg. The array length behaviour gotcha). Rick > > ~TJ
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