From: James Dinkel <jdinkel@...>
Date: 2008-08-19T14:21:53+09:00
Subject: passing a variable from a block back to the method

I have several files that I have to read, check the contents, and then
write any changes.  I overloaded the File class to help me out with
this:

----------------------------------------------------------
class File

  def self.change(filename)

    # read the file, execute a block, then write the file
      File.open(filename, 'r+') do |file|
        lines = file.readlines
        yield lines
        # return if not changing anything
        file.pos = 0
        file.print lines
        file.truncate(file.pos)
      end
  end
end
----------------------------------------------------------

The method is called with:

----------------------------------------------------------
File.change('awesomefile') do |contents|
  contents.collect! do |line|
    # magic happens
    # decide not to change anything
  end
end
----------------------------------------------------------

This is a huge waste if the files don't change (as they often don't).
The problem I'm having is with the "# decide not to change anything" in
the block and passing that back to the method so "# return if not
changing anything" knows the answer.  I'm not sure if I can pass an
instance variable around to do this?  I don't really know how that would
work since I don't really have an instance of file to work with.

Maybe someone has some ideas?
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