On Wed, Apr 10, 2013 at 1:53 PM, Bob Rogers <[email protected]> wrote: > From: Gyepi SAM <[email protected]> > Date: Wed, 10 Apr 2013 13:54:06 -0400 > > On Tue, Apr 09, 2013 at 10:24:45PM -0400, Bob Rogers wrote: [...] > Because your example handles a single result, it is not clear that, > in fact, any return values MUST be collected similarly. Unless, of > course, map is used simply for side effects. > > I would hope (but don't know how to check) that Perl is smart enough to > notice that the "map" in my original example is in a void context, and > won't bother to store any return values from the block. Is that what > you mean?
Current versions of Perl are sufficiently smart to not build a return list. You can verify by creating objects with destructors inside the map and seeing when they get destroyed. > > It's hard to think of a case where this would be better than a simple > > loop, which is both smaller and more readable. However, this technique > > also gives you an early exit when mapping over a tree recursively. > > Even then, the need to handle collected values manually would seem to > obviate any advantage in doing so. > > Over the years, I have seen many applications for mapping over trees > (and also written a few), and most of them just produce side effects, > either to the tree or externally. Those that don't tend to be of the > nature "collect (or count) all nodes that satisfy X," for which a > non-local exit would defeat the purpose. Those that do require > non-local exit are of the form "find the *first* X" or "return true if > *any* X," where the burden of handling a scalar return is minimal and > the benefit from being able to skip the remainder of the tree is clear. Many also are of the form, "Start where you left off, give me the next one." That gets you into internal versus external iterators. > In other words, I believe the "collect values" cases and the > "nonlocal exit" cases are effectively disjoint. I've never found the > need for (e.g.) a "collect the first N nodes that satisfy X" routine. Returning paginated results in a web page. > This discussion has confirmed, for me, that writing code is, in many > ways, similar to writing prose. Though there may initially, appear to > be many ways to communicate, thoughtfulness, good taste and > circumstance quickly show that there are only a few good ways to do > so. > > -Gyepi > > To the extent that there are vastly more ways to write bad (code|prose) > than good, I heartily agree. But I submit that that still leaves an > enormous field of possibilities. Of course, I always try to write the > best (code|prose) I can, subject to constraints, of course, and it often > seems to me that there's only a few acceptable solutions, maybe only > one. But I have strong preferences in coding style, so I suspect that's > just my biases showing. I absolutely agree. There is not just one right way. > Sorry to come back at you with so much disagreement; that was not my > intention. > > -- Bob > > _______________________________________________ > Boston-pm mailing list > [email protected] > http://mail.pm.org/mailman/listinfo/boston-pm _______________________________________________ Boston-pm mailing list [email protected] http://mail.pm.org/mailman/listinfo/boston-pm
