On Saturday, 24 March 2018 at 05:55:53 UTC, Chris Katko wrote:
On Saturday, 24 March 2018 at 03:04:41 UTC, Andrei Alexandrescu
wrote:
On 3/23/18 7:29 PM, H. S. Teoh wrote:
Well, looking at the implementation of std.getopt turned up
the
disturbing fact that the program's argument list is actually
scanned
*multiple times*, one for each possible option(!). Besides
the bogonity
that whether or not searchPaths will be set prior to finding
-l depends
on the order of arguments passed to getopt(), this also
represents an
O(n*m) complexity in scanning program arguments, where n =
number of
arguments and m = number of possible options.
And this is not to mention the fact that getoptImpl is
*recursive
template*. Why, oh why?
Am I the only one who thinks the current implementation of
getopt() is
really stupid?? Can somebody please talk some sense into me,
or point
out something really obvious that I'm missing?
Affirmative. The implementation is quadratic (including a
removal of the option from the string). This is intentional,
i.e. understood and acknowledged while I was working on it.
Given that the function is only called once per run and with a
number of arguments at most in the dozens, by the time its
complexity becomes an issue the function is long beyond its
charter.
This isn't the only instance of quadratic algorithms in
Phobos. Quicksort uses an insertion sort - a quadratic
algorithm - for 25 elements or fewer. That algorithm may do
600 comparisons in the worst case, and it's potentially that
many for each group of 25 elements in a large array.
Spending time on improving the speed of getopt is
unrecommended. Such work would add no value.
Andrei
Is there a possibility of improving this function?
- While quadratic, for low N, quadratic isn't a big deal. So
at what point does quadratic for this function become "a
problem"?
- If it is a problem, what's stopping someone from improving
it?
Last question though, is there any kind of list of features,
and minor features and fixes that can or need to be done?
Perhaps it already exists, but it seems like it'd be great to
have a wiki of contribution sites (like this function) that
someone could just browse and go "Hey, I know how to do X,
maybe I'll take a crack at it." That way, devs who don't have
time to improve something "low on the list" could still
outsource it in a clear list instead of people who just happen
to see it on the forum at the right place right time.
Yes, Bugzilla is full of excellent ideas:
https://issues.dlang.org/buglist.cgi?component=phobos&list_id=220544&product=D&resolution=---
There are even some tags like "bootcamp" for someone who is
looking to get started:
https://issues.dlang.org/buglist.cgi?component=phobos&keywords=bootcamp%2C%20preapproved&keywords_type=anywords&list_id=220545&product=D&query_format=advanced&resolution=---
We have also recently started to experiment with GitHub's new
project dashboards. Currently they are tracking projects like
improving the documentation, @safe-ty, DIP1000 etc.:
https://github.com/dlang/phobos/projects
DMD has a similar set which is based on Walter's recent post [1]
https://github.com/dlang/dmd/projects
Last, but not least there's a "Get involved" guide at the wiki:
https://wiki.dlang.org/Get_involved
As you couldn't find any of these pages, please let us know where
you looked first, so that maybe we can make it easier for future
people to find this information ;-)
[1] https://forum.dlang.org/post/[email protected]
