Re: Ruby, OO newb, subclassing question

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* Newbie (saleo / bellsouth.net) wrote:
> I am a Ruby, OO newbie. I mostly work with databases. I am trying to use
> ruby for scripting some of my routine tasks.
> 
> I am trying to sub class a File, to create a HtmlReportFile with
> additional methods.
> 
> class HtmlReport < File
> 
>   def initialize(filename)
>     open(filename,'w')    #Don't know why this does not return a file
> object
>   end
[snipped]

Initialize doesn't return a value; it's called when the object is
instantiated (created).  So the return value from open is disappearing
into thin air.

The "correct" way to do this is to use "super" to pass the appropriate
arguments to File#initialize, like so:

  # load CGI library (for CGI.escapeHTML)
  require 'cgi'

  class HtmlReport < File
    HEADER = '<html><head><title>%s</title></head><body>'
    FOOTER = '</body></html>'

    def initialize(path)
      # call File#initialize with the correct arguments
      super(path, 'w')
    end

    def header(title)
      # HTML-escape the report title
      self.puts HEADER % CGI.escapeHTML(title)
    end

    def content(text)
      self.puts text
    end

    def footer
      self.puts FOOTER
      close
    end
  end

[snipped]
> if $0 == __FILE__
>   my_report = HtmlReport.new('test.html')
>   my_report.header('Test report')
>   my_report.content('Some text')
>   my_report.footer
> end

With the code I pasted above, running your test code produces a file
called test.html that looks like so:

  <html><head><title>Test report</title></head><body>
  Some text
  </body></html>

Hope that helps...

-- 
Paul Duncan <pabs / pablotron.org>        pabs in #ruby-lang (OPN IRC)
http://www.pablotron.org/               OpenPGP Key ID: 0x82C29562

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