[semiquaver]

You’re quite right. OP’s rewrite contains a bug: it leaks one file descriptor per invocation. The correct version passes a block to `open` directly so that it’s automatically closed when the block is done executing. Maybe golfing down to be “idiomatic” isn’t always best :)

  Dir.open('.') do |dirp|
    dirp.each do |f|
      puts f if f.match?(/\.rb\z/)
    end
  end

https://ruby-doc.org/core-3.1.0/Dir.html#method-c-open

There are a few ruby stdlib classes like Tempfile that use the finalizer trick you mention to free resources on GC but Dir isn’t one of them. Here’s it’s implementation:

https://github.com/ruby/ruby/blob/1a24442193fe437e761e941d1a...