as discussed before, the problem with setDefault() approach you are suggesting is that the dict(), at least in JS, will be created in any case.
var newDict = a.setDefault(k1, dict()); above operation will invoke dict() regardless k1 was present or less and this is not good for anyone: RAM, CPU, GC, etc the initial pattern is and wants to be like that so that not a single pointless operation is performed when/if the key is already there. var o = obj.has(key) ? obj.get(key) : obj.set(key, dict()); // <== see dict, never called if key quick and dirty var o = obj.get(key) || obj.set(key, dict()); With current pattern, and my only concern is that after this decision every other `set()` like pattern will return this even where not optimal, I have to do var o = obj.has(key) ? obj.get(key) : obj.set(key, dict()).get(key); meh ... but I can survive :D On Tue, Dec 4, 2012 at 4:49 PM, Tab Atkins Jr. <jackalm...@gmail.com> wrote: > On Mon, Dec 3, 2012 at 2:21 PM, Andrea Giammarchi > <andrea.giammar...@gmail.com> wrote: > > IMHO, a set(key, value) should return the value as it is when you > address a > > value > > > > var o = m.get(k) || m.set(k, v); // o === v > > > > // equivalent of > > > > var o = m[k] || (m[k] = v); // o === v > > If this pattern is considered sufficiently useful (I think it is), we > should handle it directly, as Python does. Python dicts have a > setDefault(key, value) method which implements this pattern exactly - > if the key is in the dict, it returns its associated value (acts like > a plain get()); if it's not, it sets the key to the passed value and > then returns it. Using this pattern is not only clearer, but avoids > repetition (of "m" and "k" in your example), and actually chains - I > use setDefault all the time when working with nested dicts. > > (For example, if I have a sparse 2d structure implemented with nested > dicts, I can safely get/set a terminal value with code like > "a.setDefault(k1, dict()).set(k2, v)". If that branch hadn't been > touched before, this creates the nested dict for me. If it has, I > create a throwaway empty dict, which is cheap. If JS ever grows > macros, you can avoid the junk dict as well.) > > I prefer the plain methods to work as they are currently specified, > where they return this. > > ~TJ >
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