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Ruby, OO newb, subclassing question

Newbie

2/13/2007 7:12:00 PM

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

def header(title)
html_head = <<-EOF_HTML_HEAD
<html>
<head><title>#{title}</title>
</head>
<body>
EOF_HTML_HEAD
puts html_head #shouldn't this write to self(file)??
end

def content(text)
puts text
end

def footer
puts '</body></html>'
close
end

end


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


But running the above returns the following error:


c:\code\ruby\sample>ruby test2.rb
test2.rb:11:in `write': uninitialized stream (IOError)
from test2.rb:11:in `header'
from test2.rb:28


Can somebody please tell me How it needs to be done.

Thanks
Saleo

--
Posted via http://www.ruby-....
2 Answers

Paul Duncan

2/13/2007 7:36:00 PM

0

* 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.pabl... OpenPGP Key ID: 0x82C29562

ramalho@gmail.com

2/13/2007 7:40:00 PM

0

On 2/13/07, Newbie <saleo@bellsouth.net> wrote:
> def initialize(filename)
> open(filename,'w') #Don't know why this does not return a file object
> end

It does return a file, but you don't do anything with it... initialize
is not used to create an instance, but only to initialize de
attributes of an instance created by Ruby when you invoke
HtmlReport.new. So you'd have to assign the opened file to an instance
variable of your classe to avoid loosing the reference to it.

But the problem is deeper than that. I would not want to subclass
File. Subclassing is cool and very attractive when you first study OO,
but it's not the right solution in many cases.

Cheers,

Luciano