bluefeet Yet another Perl Hacker weblog

use Path::Class;

The CPAN (Comprehensive Perl Archive Network) distribution, Path::Class, provides a simple OO API alternative to the built-in perl file IO functions such as open, opendir, stat, etc. Code written to use Path::Class tends to be smaller (concise, easier to maintain, etc) than similar code that uses the standard built-in functions.

Here is an example of how a small utility might be written without Path::Class:

And here it is re-written to use Path::Class:

Using Path::Class is a no-brainer when you compare `(stat "$dir/$file")[7]` with `$file->stat->size()`.

One of Path::Class’s greatest stengths is that it is very simple and many of the features it provides are done so by glueing with other well-tested modules that have been on CPAN for a long time. These modules include IO::Dir, IO::File, File::Path, and File::stat.

Some other highlights include:

• Has a recurse() method that provides an enhanced File::Find-like interface.
• Works equally well with absolute and relative paths, and can correctly convert between the two.
• Symlinks are handled correctly and there are methods to interact with them.
• Works equally well under different operating systems, such as Linux and Windows.
• The interface, for me anyway, is about as intuitive as it gets. Very well designed to DWIM.

I’ve been using this module at $work for a while now and am very happy with it and have had coworkers tell me, after they gave it a try, how much cleaner their code ended up being because they used this module.

Enjoy!

XS Hits Newb; Bystanders Watch in Dismay

Last year I wrote GIS::Distance::Fast to provide some much needed speedups to the pure-perl GIS::Distance. This ::Fast version used Inline::C which isn’t all that optimal and was just a scapegoat for doing the right thing.

So, this evening I rolled up my sleeves and went to work. I first looked at a module I already knew to use XS, Cache::Memcached::Fast. That was overwelming.

Then I went on over and read through the perlxs and perlxstut docs. I was STILL floundering about not sure what to do. I then took a whack at using SWIG (Simplified Wrapper and Interface Generator). OhMyGodz I’m feeling overwhelmed now and still nothing works. I’m not going to even document my attempts up until this point.

I then found this document that goes in to more detail about using SWIG with Perl. The thing about this document that helped me so much is that in section 2, Perl Extension Building, it had the simplest example I had yet run in to, and it made sense! Its kinda funny that a SWIG document was what taught me how to write my own XS without using SWIG. :)

An XS distribution can contain as little as two files (well, beyond the usual Makefile.PL, etc). A single .pm file and a .xs file is enough. You can get more complex, if you want, of course. Once you’ve written your Module.xs file you can run it through xssubpp Module.xs > Module.c to see what the .c file looks like and to verify that your .xs file is correct.

Note that xssubpp may complain about you using types that aren’t in your typemap. This is because xssubpp doesn’t know how to find your system’s typemap file. You can specify a typemap file using the -typemap switch. The file is located somewhere in your perl lib path as ExtUtils/typemap.

So, let’s go for an example. Let’s make an XS module that convert hours to minutes. I structure all my code and files as if they would be distributed as a CPAN module. This has added benefits as you’ll see in a moment.

convert-hoursminutes/lib/Convert/HoursMins.pm:

convert-hoursminutes/HoursMins.xs:

convert-hoursmins/Makefile.PL

convert-hoursmins/t/00_basic.t

Now lets see if it worked:

Bottom line for me is XS isn’t all that hard when your C code isn’t all that complex. SWIG is overkill for small stuff. But for large swaths of C code I bet SWIG saves lives. Also, XS is a little arcane, but its not too bad.