Ruby 1.9 can check your indentation

All Ruby programmers regularly encounter the mystical error “syntax error, unexpected $end, expecting keyword_end.” We know what it means: we left off an end somewhere in the code. As Ruby compiled our source, it keeps track of nesting, and when it reached the end of file ($end), it was expecting to see one more end keyword, and none was there.

So, we trundle back through the source, and after a while discover we’d deleted just one too many lines during that last edit.

Ruby 1.9 makes that easier. For example, here’s a source file:

class Example
  def meth1
    if Time.now.hours > 12
      puts “Afternoon”
  end
  def meth2
    # …  
  end
end

Run it through Ruby 1.9, and you’ll get the same old error message:

dave[RUBY3/Book 8:26:48] ruby t.rb
   t.rb:10: syntax error, unexpected $end, expecting keyword_end

But add the -w flag, and things get more interesting.

dave[RUBY3/Book 8:26:51] ruby -w t.rb
  t.rb:5: warning: mismatched indentations at ‘end’ with ‘if’ at 3
  t.rb:9: warning: mismatched indentations at ‘end’ with ‘def’ at 2
  t.rb:10: syntax error, unexpected $end, expecting keyword_end

It’s the small things in life…