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2015/07/26

What I learned from perlbrew

I signed up for Neil Bowers' CPAN Pull Request Challenge, and the first module I got was App::perlbrew. After some looking and guessing, gugod pointed me to one of his problems, and after some time reading and understanding how things work, I got it done.

It took me a while to figure out how it worked. I had seen and used something like it — I had found out about dispatch tables from my local friendly neighborhood Perl Mongers — and I have started to use old-school Perl object orientation on occasion, but this combined them in a very interesting way.

A lot of the clever, however, isn't where I thought it was, which I didn't realize until now. The symbol-table manipulation isn't about making the commands work, but rather guessing what you meant if you give a command it can't handle. The "magic" is all about $s = $self->can($command) and $self->$s(@$args).

I wrote a quick stub of an application that would show off how to this works, with lots of comments that are meant to explain what's meant to happen instead of how it's supposed to work, as "Most comments in code are in fact a pernicious form of code duplication".

If you try symtest.pl foo, it will print 1 and foo. If you try symtest.pl food, it'll just print 1. If you instead try symtest.pl fod, it'll print "unknown command" and suggest foo and food as alternate suggestions. Like a boss.

One of the coolest things, I think is that you can put your user-facing methods in a second module. Or, perhaps I just have a low threshold for cool.

If you have questions about the code, or understand the things I handwave and know you can do better, please comment below.