One of the fun weird aspects of Ruby is that you can mix code and data together in the same file. Here’s a trivial example:

DATA.each_line do |line|
  puts line
end

__END__
I
am
Groot

If you put the snippet above in a file named groot.rb and run with ruby it will output the following:

I
am
Groot

So, what happened? Basically the __END__ token marks the end of the Ruby code in a source file and everything afterwards is treated as data and bound to an special IO object named DATA (of type File).

That’s one of the many weird features that Ruby inherited from Perl1 and is useful when you’re playing with a single-file script and you need some test data.2 Not the most useful feature in a Rails application, though.

Note that this trick works only for the file you’ve loaded directly in the interpreter and it won’t work for any files that are referred (e.g. with require) by it - the DATA object will be empty for them.

That’s all I have for you today. Keep Ruby weird!

  1. See https://perldoc.perl.org/perldata#Special-Literals ↩

  2. Might be pretty useful for https://adventofcode.com/ ↩