Just in case any of you wonder why when you use REXML’s write method on ruby 1.8.6 (2007-09-24 patchlevel 111) [universal-darwin9.0] and possibly other versions, you get errors, it’s a bug in Apple’s REXML library. See this:

def write(writer=$stdout, indent=-1, transitive=false, ie_hack=false)
  Kernel.warn("#{self.class.name}.write is deprecated. See REXML::Formatters")
  formatter = if indent > -1
    if transitive
      REXML::Formatters::Transitive.new( indent, ie_hack )
    else
      REXML::Formatters::Pretty.new( indent, ie_hack )
    end
  else
    REXML::Formatters::Default.new( ie_hack )
  end
  formatter.write( self, output )
end

As you can see, the method sets a local variable of ‘writer’ in the method arguments, however at the bottom it uses ‘output’. A simple change of the bottom line fixes it:

formatter.write( self, writer )

For those who requested it, here’s how to use the formatter:

# I want to create a REXML document to output
require "rexml/document"

# Make a pretty formatter
formatter = REXML::Formatters::Pretty.new( 2 )

# Create some silly xml example
xml = REXML::Document.new '<moo>RAR!</moo>'

# Write to STDOUT
formatter.write( xml, $stdout )

# Write to file
xml_file = File.open( "some_file.xml", "a+" )
formatter.write( xml, xml_file )