Ruby Snips

This next snip was brought to my attention by Peter Cooper, of Ruby Inside fame. This snip is posted on DZone’s new snippet site, formerly Peter’s snippet site.

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class Fixnum
  def prime?
    ('1' * self) !~ /^1?$|^(11+?)\1+$/
  end
end

The method prime? is being mixed (via open class) in with Fixnum (a Ruby class) to extend it so that simple calls likes the follow now become possible:

 1.prime?

The method will return either true or false, depending if the number is a prime number or not. This is a prime :) example of the power of Ruby’s open class feature. You can add any method to any class that you choose. Also, it demonstrates Ruby’s conciseness – 1 line of code (regular expression!) and you can now call that method on any number.

If you have a favorite piece of Ruby/Rails code or have seen a piece, drop me a line at revans [at] robertrevans ]dot[ com and it may be featured here.

Update As Brian Smith pointed out in the comments, this isn’t a true mixin, as I stated, because the prime is not included with a module that is then include within the Fixnum Class. You see, Module’s don’t have instance methods as classes do, but if you include a Module within a class, those methods within the Module are “mixed in” with the Class that is including the Module.