On Tue, Oct 16, 2012 at 4:06 PM, Yehuda Katz <[email protected]> wrote:
> On Tue, Oct 16, 2012 at 6:26 PM, Mark S. Miller <[email protected]>wrote: > >> Getting the comments with a getter seems fine. Appending only the list of >> comments with a setter is bad, as it does not resemble storage semantics. > > > Do you mean appending only *to* to list of comments? > Yes. > > `comment.post = post` has similar semantics to setting a foreign key in a > SQL database, which will (obviously) update future requests for "all > comments with post_id=post.id". Bidirectionally linked one-to-many > relationships are pretty common, and it's desirable for the relationships > to remain in sync automatically. I don't think this is the right heuristic > for moving to a method. > > I would expect well written setters to at least be idempotent, and well >> written getters to be side effect free. > > > comment.post = post is, of course idempotent. Setting it to the same value > as it already has would have no effect. > Good. In light of this, I reread the original post of your example. I had misunderstood it. I strongly agree with those earlier posts saying that we should have some well thought out design guidelines for when to use an accessor vs a method, and that accessor usage should only be "storage-like". However, now that I understand it, I also agree that your example is storage-like enough to my eyes that I would like guidelines that permit it as a normal case. I do not yet a concrete suggestion other than "getters should be query-only" and "setters should be idempotent and not cause 'external' effects (other than notifying registered observers)." The key thing about your example is "What does external mean?" I don't yet have an answer to offer. These guidelines are not prescriptive on any external JS community. But we need guidelines for APIs designed by TC39 and (hopefully eventually) by w3c. -- Cheers, --MarkM
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