Strings, arrays, and duck typing goodness

February 14, 2006

We use more and more ruby around my shop every day, and that just tickles me pink. One thing that we’ve been using it a lot for is managing our Subversion working copies. We have a script that will delete unversioned files. We have a script that will delete ignored files. I wanted to write a script that would do both of those things and also revert any modified files (thus returning the working copy to a pristine state, essentially).

There was a lot of duplication between the two scripts. In fact, the only thing different was one character in a regex: it was ‘?’ for the unversioned and ‘I’ for the ignored. I went through and wrote a new class to represent these things and then I wanted to write a method named delete_if_status which would take a list of statuses and delete any items in the checkout that matched any of them.

I thought it would be cool if I could call it like this:

list.delete_if_status(['?', 'I'])

But also call it like this:


Naturally, I figured Ruby would have a duck-typing answer to this problem, but just the way it solved it surprised me (just a little–actually, now that I think about it, it’s unsurprising). Here is an IRB log that demonstrates just what I discovered.

irb(main):001:0> 'I?'.split
=> ["I?"]
irb(main):002:0> 'I?'.split('')
=> ["I", "?"]
irb(main):003:0> 'I?'.to_a
=> ["I?"]
irb(main):004:0> ['I','?'].to_s
=> "I?"
irb(main):005:0> ['I','?'].to_s.split('')
=> ["I", "?"]

So what I ended up with was this method:

def delete_if_status(spec)
  status_list = spec.to_s.split('')
  self.delete_if do |item|
    status_list.include? item.status

I love Ruby.

Edited: Fixed some formatting with code and output snippets.

Layout, design, graphics, photography and text all © 2005-2010 Samuel Tesla unless otherwise noted.

Portions of the site layout use Yahoo! YUI Reset, Fonts & Grids.