On Tue, Oct 16, 2012 at 2:43 PM, Allen Wirfs-Brock <[email protected]> wrote: > On Oct 16, 2012, at 2:36 PM, Tab Atkins Jr. wrote: >> On Tue, Oct 16, 2012 at 2:24 PM, Allen Wirfs-Brock >>> >>> You might not agree with the above guideline, or choose to follow it. >>> That's fine. But, what you you propose as an alternative. What are your >>> guidelines for choosing to use an accessor rather than a method? If you >>> consider you example to be a reflection of "good design" what are the >>> specific design principles it is following. Why is that an appropriate >>> place to use an accessor. >> >> I consider Yehuda's example to be a perfectly fine and completely >> normal place to use an accessor. *Accessing* the list of comments >> attached to a post is conceptually a side-effect-free operation. >> While it can change over time, it only does so due to obvious actions >> - querying it twice, one immediately after the other, *will* give === >> results. >> >> *Setting* the attribute may have side-effects, but reasonable ones >> (setting/unsetting Comments.post or Post.comments on other objects). >> This is a reasonable thing for a setter to do. >> >> I don't see any reason to make these two into methods. > > So, what are the design guidelines that you would apply leads to these being > accessors? When do you use a method? When do you use an accessor?
As getters, I think it's self-explanatory. They're idempotent and effect-free. As setters, they do go beyond what Brendan suggested in his original formulation, but the effects still feel reasonably "local" to me. Whether the setter is considered to have non-local effects or not is actually just a question of implementation, not essence - we could implement the setter simply and naively, and have the getters do an expensive tree traversal to assemble the answer, or have the getter be simple and naive, and have the setter reach in and do some mutations to maintain the state of the tree. ~TJ _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
